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COVER

Includes the full-length DVD
movie "Hubble - 15 Years of
Discovery"


This book forms part of the European Space Agency's 15th anniversary
celebration activities for the 1990 launch of the NASA/ESA Hubble Space
Telescope.

As an observatory in space, Hubble is one of the most successful scientific
projects of all time, both in terms of scientific output and its immediate
public appeal.

Hubble has exploited its unique scientific capabilities where no other
instruments can compete. It consistently delivers super-sharp images and
clean, uncontaminated spectra over the entire near-infrared and ultraviolet
regions of the electromagnetic spectrum. This has opened up new scientific
territory and resulted in many paradigm-breaking discoveries.

Exquisite quality images have enabled astronomers to gain entirely new
insights into the workings of a huge range of different astronomical
objects. Hubble has provided the visual overview of the underlying
astrophysical processes taking place in these objects, ranging from planets
in our Solar System to galaxies in the young Universe.

Astronomy is fortunate in that telescopes not only produce results of great
scientific value, but also of eye-catching beauty and artistic potential.
This book shows the close relationship between the two at its best.

Hubble's design remains unique amongst space-based observatories by
enabling astronauts to regularly maintain and upgrade it during Space
Shuttle Servicing Missions. These have not only kept the telescope at the
forefront of scientific capability, but have transformed its performance to
heights beyond the dreams of its original designers.




Lars Lindberg Christensen
Lars is a science communication specialist heading the Hubble European
Space Agency Information Centre group in Munich, Germany where he is
responsible for public outreach and education for the NASA/ESA Hubble Space
Telescope in Europe.

Lars obtained his Master's Degree in physics and astronomy from the
University of Copenhagen, Denmark. Before assuming his current position, he
spent a decade working as a science communicator and technical specialist
for Tycho Brahe Planetarium in Copenhagen.

Lars has more than 100 publications to his credit, most of them in popular
science communication and its theory. His other productive interests lie in
the areas of graphical communication, written communication, technical
communication and scientific communication. He is the author of "The Hands-
On Guide to Science Communication" (Springer) as well as the co-author of a
colourful book on light phenomena in nature. He has produced material for a
multitude of different media from star shows, laser shows and slide shows,
to web, print, TV and radio. His methodology is focussed on devising and
implementing innovative strategies for the production of efficient science
communication and educational material. This work involves working with
highly skilled graphics people and technicians, some results of which are
visible at: www.spacetelescope.org.

Lars is a founding member and secretary of the International Astronomical
Union Working Group on "Communicating Astronomy with the Public"
(www.communicatingastronomy.org), manager of the world-renowned
"ESA/ESO/NASA Photoshop FITS Liberator" project, Outreach & Education
Coordinator for the "Astrophysical Virtual Observatory" and is the
Executive producer and director of the science documentary movie "Hubble -
15 Years of Discovery".

Bob Fosbury
Bob works for the European Space Agency as part of ESA's collaboration with
NASA on the Hubble project. Carried out in collaboration with the European
Southern Observatory (ESO) near Munich in Germany, this work benefits
greatly from the unique scientific environment that ESO provides. He
started doing this in 1985, more than 5 years before launch and so has been
involved in this huge project for quite a while. During the latter part of
this period, Bob served on NASA's Ad Hoc Science Working Group and ESA's
Study Science Team as they developed the instrument concepts for the James
Webb Space Telescope, the next generation of space observatory.

Bob has published over two hundred scientific papers on topics ranging from
the outer atmospheres of stars, the nature of quasars and active galaxies
to the physics of forming galaxies in the most distant reaches of the
Universe. He started his career at the Royal Greenwich Observatory (RGO) in
Herstmonceux, England in 1969 and was awarded his DPhil by the nearby
University of Sussex in 1973. He then became one of the very first Research
Fellows at the newly constructed Anglo Australian Observatory 4 metre
telescope in New South Wales, Australia before going to ESO while it was
based at CERN in Geneva, Switzerland. He then had a spell of 7 years as a
staff member at the RGO, working on instruments for the new observatory on
La Palma in the Canary Islands and on the pioneering Starlink astronomical
computer network.

Bob is currently chairman of the ESO Astronomy Faculty, the largest group
of professional astronomers in Europe (and Chile), and is active in the
close liaison between the ESO and ESA science programmes. He has had a
lifelong interest in the study of natural phenomena of all kinds and is
particularly interested in atmospheric optics and the origin of natural
colour.


Martin Kornmesser
Martin got his degree in graphics design in Munich in 1989. In those days,
computers were not yet the favourite tools of graphic designers and,
through the nineties, Martin actively pioneered the exploration of the
fascinating and newly emerging world of computer graphics.

In 1990 Martin Kornmesser was the co-founder of the company ART-M, where he
created illustrations, wall-paintings and all kinds of graphics design
before joining ESA's Hubble Space Telescope outreach group in 1999.

P1

HUBBLE
15 YEARS OF DISCOVERY
By Lars Lindberg Christensen & Bob Fosbury
Illustrations and Layout by Martin Kornmesser

This book is dedicated to all the hard working people in the USA and Europe
who have made the Hubble Space Telescope an incredible scientific success

P2

caption:
The Sombrero Galaxy

The Sombrero galaxy is one of the Universe's most stately and photogenic
galaxies. The galaxy's hallmark is a brilliant white, bulbous core
encircled by thick dust lanes comprising the spiral structure of the
galaxy.

Credits:
NASA/ESA and The Hubble Heritage Team (STScI/AURA)

P3

Table of Contents

Foreword by Malcolm Longair 5

Preface 7

Introduction 9

1 The Hubble Story 11

2 Hubble Up Close 21

3 Planetary Tales 29

4 The Lives of Stars 39

5 Cosmic Collisions 59

6 Monsters in Space 71

7 Gravitational Illusions 81

8 Birth and Death of the Universe 89

9 Looking to the end of time 97

10 Hubble Gallery 105


P5

FOREWORD

The Hubble Space Telescope has undoubtedly had a greater public impact than
any other space astronomy mission ever. The images included in this
beautiful volume are quite staggering in what they reveal about the
Universe we live in and have already become part of our common scientific
and cultural heritage.
But what about the science impact? It is no exaggeration to say that the
scientific output of the mission has far exceeded the most optimistic
expectations of all those involved in the planning and execution of the
project. When I joined the project in 1977, I had to describe the astronomy
programme I would carry out with the Hubble once it was in operation in
orbit. Seventeen years later when I received my first data, I was quite
staggered by the quality of the images and also by the totally new science
which they revealed about the ways in which relativistic jets can
illuminate the environments of active galaxies. This is a repeated theme in
essentially all areas explored by the Telescope. The images are not only
beautiful, but are full of spectacular new science, much of it undreamed of
by the astronomers involved. A good example is the discovery of
protostellar discs seen in silhouette against the bright background of the
Orion Nebula. Another is the ability to discover distant star forming
galaxies by imaging in a number of wavebands. The observation of distant
supernovae has enabled the present acceleration of the Universe as a whole
to be measured - an undoubted triumph. And then there are the spectacular
images of the Hubble Deep and Ultra-Deep Fields which have revealed what
are almost certainly young galaxies in the process of forming the galaxies
and larger scale structures we observe about us today. But these are only a
few random samples of the wealth of scientific knowledge which has accrued
from the mission. Every picture tells a wonderful story which has already
been built into our picture of the evolving Universe.
What are the lessons to be learned from this spectacular success? The route
to new understanding is through the ability to observe the Universe in new
ways with techniques, that extend observational capability by a factor of
10 or more. In the case of the Hubble Space Telescope, the gains in angular
resolution, or sharpness, and corresponding sensitivity, as well as the
remarkable stability of the instruments in the remote environment of space,
have given it unprecedented power to uncover new astrophysics. The results
are a wonderful tribute to the dedicated efforts of many scientists,
astronomers, engineers, managers and administrators, as well as to the
vision of NASA and ESA in enabling the Hubble Space Telescope to come
about. Long may this vision and the ability to inspire the public
imagination continue as an essential means of deepening our understanding
of the Universe.

Malcolm Longair

4 April 2005

caption:

NGC 346

Hubble's exquisite sharpness has plucked out an underlying population of
infant stars embedded in the nebula NGC 346 that are still forming from
gravitationally collapsing gas clouds.

Credits:

NASA, ESA and A. Nota (STScI/ESA)

P7

PREFACE

This book takes a closer look at what may be the world's most successful
scientific project, 15 years after the launch of the Hubble Space
Telescope. In many ways the science from Hubble is a journey through time
and space.
We would like to thank Stefania Varano, Stuart Clark and Anne Rhodes who
all worked on the film manuscript that laid the foundation for important
parts of this book.
Unless otherwise noted, the images in this book were taken by the NASA/ESA
Hubble Space Telescope and should be credited to NASA, ESA and the
individual scientists (see www.spacetelescope.org for the exact details).
The DVD mounted on the back contains the movie "Hubble - 15 Years of
Discovery" that ESA has produced in collaboration with partners all over
Europe. It is an 83 minute journey through the history, the troubled early
life and the ultimate scientific successes of Hubble. The soundtrack was
especially composed for the movie. In addition there are more than 60
minutes of bonus material. The narration is available in three languages:
English, German and Greek. There are subtitles in 15 languages: Bulgarian,
Dansk, Deutsch, Greek, EspaЯol, FranГais, Italiano, Nederlands, Norsk,
Polski, PortuguИs, Russian, Suomi and Svenska. More information about
Hubble can be found on ESA's Hubble Internet site: www.spacetelescope.org


Lars Lindberg Christensen and Bob Fosbury
Munich, 8 April 2005

Caption:

The Cone Nebula

Radiation from hot, young stars (located beyond the top of the image) has
slowly eroded the nebula over millions of years. Ultraviolet light heats
the edges of the dark cloud, releasing gas into the relatively empty region
of surrounding space.

Credits:

NASA, Holland Ford (JHU), the ACS Science Team and ESA

P9

Introduction

On 24 April 2005 the NASA/ESA Hubble Space Telescope will exceed its
original estimated lifetime of 15 years in orbit around the Earth. Hubble
has been hugely successful in many different areas of astronomy. How does
it differ from other famous telescopes?
Hubble orbits 600 km above the Earth's surface, placing it well above our
image-distorting atmosphere. It can be upgraded to take advantage of the
latest developments in instrumentation and software. The telescope is
designed to take high-resolution images and accurate spectra by
concentrating light to form sharper images than are possible from the
ground, where the atmospheric 'twinkling' of the stars limits the clarity.
Therefore, despite its relatively modest aperture of 2.4 metres, Hubble is
more than able to compete with ground-based telescopes that have light-
collecting (i.e. mirror) areas 10 or even 20 times larger.
As well as being able to take sharper wide-field images, the other huge
advantage Hubble has over ground-based telescopes is its ability to observe
the near-infrared and ultraviolet light that is otherwise filtered away or
masked by the atmosphere before it can reach the ground.
In many areas of astronomical investigation, Hubble has pushed the limit of
our knowledge far, far beyond anything possible before its launch.

Caption:

NGC 1300

NGC 1300 is considered to be prototypical of barred spiral galaxies. Barred
spirals differ from normal spiral galaxies in that the arms of the galaxy
do not spiral all the way into the centre, but are connected to the two
ends of a straight bar of stars containing the nucleus at its centre.

Credits:

NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

P11

1 The Hubble Story

Hubble finally allowed astronomers to realise their dream of escaping the
distorting effects of the Earth's atmosphere to make their observations.
Achieving an operational observatory in space was no small task: it took
decades of planning and construction in a project of such scale and cost
that it demanded international collaboration and the work of many dedicated
engineers and scientists. The concept of a telescope that could be upgraded
and serviced regularly by astronauts has resulted in capabilities and
scientific discoveries far beyond the expectations of the designers.

Caption:

Hubble in Dock
The Hubble Space Telescope in the Shuttle's payload bay during Servicing
Mission 3A.

Credits:

NASA

P12

For many years astronomers
longed for an observatory in space

Hubble has vastly improved our view of the skies, sharpened our perception
of the Universe, and allowed us to penetrate ever deeper toward the
furthest edges of time and space.
Looking at the night sky we see the familiar twinkle of starlight; light
that has travelled enormous distances to reach us. But the stars themselves
do not flicker. The Universe is gloriously transparent, allowing light from
distant stars and galaxies to travel unchanged across space for thousands,
millions, even billions of years. Then, in the last few microseconds before
the light reaches our eyes, the fine details in the view of those stars and
galaxies are snatched away. This is because, as light passes through our
atmosphere, the ever changing blankets of air, water vapour and dust, blur
the image that finally reaches us.
To solve this problem, astronomers around the world longed for an
observatory in space for many years. As early as 1923, the famed German
rocket scientist Hermann Oberth suggested a space-based telescope. However,
it was decades before technology caught up with the dream. The American
astronomer Lyman Spitzer proposed a more realistic plan for a space
telescope in 1946.
From a position in space above the Earth's atmosphere, a telescope could
detect the pristine light from stars, galaxies, and other objects before
their images become distorted by the air we breathe. The result: much
sharper images than even the largest telescopes on the ground could
achieve; images limited in sharpness only by the quality of the optics.
In the 1970s, NASA - the National Aeronautics and Space Administration -
and ESA - the European Space Agency - began working together to design and
build what would become the Hubble Space Telescope. The name is a tribute
to Edwin Powell Hubble, the founder of modern cosmology, who, in the 1920s,
first showed that not all we see in the sky lies within the Milky Way.
Instead, the cosmos extends far, far beyond. Hubble's work changed our
perception of mankind's place in the Universe forever and the choice of
naming this most magnificent telescope after Edwin Hubble could not have
been more appropriate.

P13

Caption:

Above the Ocean of Air

A ground-based telescope similar in size to Hubble produced the image of
the barred galaxy NGC 1300 on the left. From its position in space above
the Earth's atmosphere, Hubble obtained the picture on the right of the
same galaxy. A technique called 'Adaptive Optics' can be used to sharpen
ground-based images and is extremely effective when used with telescopes
much larger than Hubble (see box below).

Box left:

Why is Hubble in orbit around the Earth?

The Earth's atmosphere both absorbs and emits light. Beyond the blue end of
the visible spectrum, the presence of ozone ensures that little ultraviolet
light reaches the ground. Towards the red end and beyond, into what
astronomers call the near-infrared spectrum, there is considerable
absorption by water vapour and molecular oxygen but also, the sky is
brightened by intense emission from the OH radical (an unstable molecule
consisting of an oxygen and a hydrogen atom). The visible spectrum alone
remains reasonably free from these effects. The entire spectral range from
ultraviolet through the near-infrared remains cleanly accessible to Hubble.

Box right

Hubble vs. Adaptive Optics

The technique of Adaptive Optics can sharpen images from large ground-based
telescopes to attain a higher resolution and is being vigorously developed
by astronomers around the World. Such observations are highly complementary
to those made by Hubble since they can exploit the collecting power of much
larger telescopes and can be used very effectively to feed such light-
hungry instruments as spectrographs. This higher resolution is achieved
over a small patch of the sky and the technique works better at infrared
wavelengths than it does in the visible spectrum used by Hubble. Hubble
remains supreme for mapping parts of the sky in exquisite detail in
ultraviolet, visible and near-infrared light.

P14

It took two decades of dedicated collaboration between scientists,
engineers and contractors from many countries before Hubble was finally
finished. On April 24, 1990, five astronauts aboard the space shuttle
Discovery left on a journey that changed our vision of the Universe for
ever! They deployed the eagerly anticipated Space Telescope in an orbit
roughly 600 km above the Earth's surface.
On Earth, astronomers waited impatiently for the first results. After
extensive technical verification and testing, it soon became obvious that
Hubble's vision was anything but sharp. The mirror had a serious flaw. A
defect in the shape of the mirror prevented Hubble from taking clear
images. The mirror's edge was too flat by only a mere fiftieth of the width
of a human hair. But to accomplish its mission, Hubble had to be perfect in
every tiny detail. The disappointment was almost too great to bear. Not
only amongst astronomers, but also for American and European taxpayers.
Nevertheless, over the following two years, scientists and engineers from
NASA and ESA worked together to design and build a corrective optics
package, named COSTAR, for Corrective Optics Space Telescope Axial
Replacement. They were also able to build in a perfect correction to the
replacement camera that was already planned for installation. Hubble's
masters now faced another tough decision: which science instrument should
they remove so that COSTAR could be fitted to Hubble? They eventually chose
the High Speed Photometer.
Hubble's First Servicing Mission, performed in 1993, has gone down in
history as one of the supreme highlights of human spaceflight. It captured
the attention of both astronomers and the public at large to a degree that
no Space Shuttle mission has since achieved. Meticulously planned and
brilliantly executed, the mission succeeded on all counts. COSTAR and the
new Wide Field and Planetary Camera 2 (WFPC2) corrected Hubble's eyesight
more perfectly than anyone had dared to hope.

Box:

Hubble's mirror problem

The cause of the problem was a defect in the 2.4 metre diameter primary
mirror caused by the incorrect assembly of the optical system used to test
the mirror during manufacture. This resulted in what is called 'spherical
aberration'. Fortunately, the test system remained untouched in the lab and
it was possible for engineers to go back and use it to reconstruct the
nature of the error with great precision. This is why the Servicing
Missions were so successful in correcting Hubble's optics to near-
perfection.

P15

Hubble was finally in business!

When the first images after the servicing came up on the computer screens
it was instantly clear that the 'glasses' taken up by the astronauts were
completely correcting Hubble's vision. Hubble was finally in business!
That was only the first time the Space Shuttle visited Hubble. The
telescope was designed to be upgraded, enabling it to take advantage of new
technologies and software. When more advanced instruments, electrical or
mechanical components became available, they could be installed by the
astronauts. So, just as a car needs servicing so Hubble needs tuning-up
from time to time. Engineers and scientists periodically send the Shuttle
to Hubble so that astronauts can upgrade it, using wrenches, screwdrivers
and power tools, just as a mechanic might with a car.
There have been four Servicing Missions so far: in 1993, 1997, 1999 and
2002. All were undertaken by astronauts transported into space by NASA's
Space Shuttle. The next one was supposed to occur in 2005, but was
unfortunately cancelled in the aftermath of the tragic Columbia crash.
Hubble's future is uncertain. It was originally designed to operate for 15
years, but it is now expected that its life could be extended to 20 years.
Hubble is still producing the most astonishing results that astronomers
have ever known.

Caption Astronaut:

Changing instruments on Hubble
An astronaut exchanging cameras on Hubble during the first Servicing
Mission in 1993.

Caption:

The centre of M100

The central regions of this grand-design spiral galaxy taken before and
after Hubble's first servicing mission. Left: A picture taken with the
WFPC1 camera in wide field mode, on November 27, 1993, just a few days
prior to the STS-61 servicing mission. The effects of optical aberration in
HST's 2.4-metre primary mirror blur starlight, smear out fine detail and
limit the telescope's ability to see faint structure. Right: The same field
imaged with WFPC2 in its high resolution channel. The WFPC2 contains
modified optics that correct for Hubble's previously blurry vision. For the
first time the telescope was able to resolve cleanly faint structure as
small as 30 light-years across in a galaxy that is tens of millions of
light years away. The image was taken on December 31, 1993.

P16

Caption:

Fine Guidance Sensor

Astronaut Gregory J. Harbaugh on the robot-arm manoeuvring a Fine Guidance
Sensor (FGS) during the second Servicing Mission.

Credits: NASA

P17

Just as a car needs servicing so Hubble
needs tuning-up from time to time

Eventually, however, Hubble's active life will end and the telescope will
have to be guided to a safe resting place in the ocean. It is too massive a
spacecraft to burn up completely in the atmosphere on re-entry and an
uncontrolled plunge into the atmosphere is a potential danger to residents
of regions covering a broad swathe of our planet. The plan is for an
unmanned probe to link up with Hubble in orbit and dock with it. The probe
will leave behind a rocket-module so that, after some more years of
fruitful observing, engineers on the ground can activate these rockets to
control Hubble's final descent into the atmosphere.
However, the retirement of the Hubble Space Telescope will not signal the
end of our unrivalled view of the Universe. Rather, it will mark a new
beginning, an era of even more amazing discoveries and images from space.
For Hubble has a successor.
The James Webb Space Telescope is currently being designed and may be
launched as early as 2011. When that day comes, scientists using the James
Webb Space Telescope hope to discover and understand even more about our
fascinating Universe.

Caption:

Space power tools

Astronaut Claude Nicollier, mission specialist from the European Space
Agency (ESA), works at a storage enclosure using one of the Hubble power
tools during the second of three extravehicular activities (EVA) of the
third Servicing Mission.

Credits: NASA

P18

Caption:

James Webb Space Telescope

Artist's impression of the James Webb Space Telescope. Shaded behind a huge
sunscreen, the telescope and its instruments will remain cool enough to
make ultra-sensitive infrared observations of the most distant objects in
the Universe.

Credits: ESA

P21

2 Hubble Up Close

Hubble is a large satellite, about the size of a school bus. As well as the
2.4 metre aperture telescope, it carries six scientific instruments that
can be regularly replaced with more modern and capable ones by space suited
astronauts in orbit 600 km above the Earth. The systems that allow it to be
pointed and stabilised are very sophisticated and are working
extraordinarily well. Far from being an isolated resource for astronomers,
Hubble has worked in close harmony with other satellites and ground-based
observatories to lead, during its 15 years of operation, a huge leap in our
understanding of the Universe.

Caption:

The NASA/ESA Hubble Space Telescope

Hubble is a large satellite; about 16 metres long or the size of a small
bus. It is also one of the most complicated pieces of technology ever
built.

Credits: ESA

P23

Hubble is a space-based telescope
that is designed to be upgraded

Hubble is a space-based telescope that is designed to be upgraded and to
adapt to changing needs and technologies. It orbits at almost 600 km above
the Earth's surface, placing it well above most of our image-distorting
atmosphere and takes about 96 minutes to complete each orbit.
It is designed to take high-resolution images and accurate spectra by
concentrating starlight to form sharper images than are possible from the
ground, where the atmospheric 'twinkling' of the stars limits the clarity.
To gather as much light as possible from the faint objects it studies, any
telescope needs the largest mirror it can get. Despite Hubble's relatively
modest mirror diameter of 2.4 metres, it is more than able to compete with
ground-based telescopes that have mirrors 10 or 20 times larger in
collecting area.
Hubble is a large satellite; about 16 metres long or the size of a small
bus. It is also one of the most complicated pieces of technology ever
built. It contains more than 3000 sensors that continually read out the
status of the hardware so that technicians on the ground can keep an eye on
everything.
Time on Hubble is a precious commodity. Astronomers across the world
regularly ask for much more time than is available. Keeping Hubble working
24/7 is no small task. Not a single second must be lost and all tasks -
either observations or so-called 'housekeeping' tasks, such as
repositioning of the telescope, or uploading new observing schedules - are
meticulously planned.

Caption:

Hubble's orbit

Hubble orbits the Earth every 96 minutes at an altitude of nearly 600 km.
The ever-changing aspect of its orbit makes the process of scheduling
observations rather complicated.

Credits P22: ESA

Box:

Is there competition between different observatories?

A large and ambitious astronomical research project today would use large
amounts of time on a whole range of different telescopes on the ground and
in space. These telescopes, far from competing with one another, provide
different and complementary views of astronomical sources that greatly
increase our ability to understand the physical processes that create them.
It is usually a case of "the whole being greater than the sum of the
parts". Hubble plays an absolutely pivotal role in many of these
programmes.

P24

Hubble'S INSTRUMENTS & SYSTEMS

Primary mirror
Hubble's primary mirror is made of a special glass coated with aluminium
and a special compound that reflects ultraviolet light. It is 2.4 metres in
diameter and collects the light from stars and galaxies and reflects it to
the secondary mirror.

FGS
Hubble has three Fine Guidance Sensors on board. Two of them are needed to
point and lock the telescope on the target and the third can be used for
position measurements, also known as astrometry.


STIS
The Space Telescope Imaging Spectrograph (STIS) is currently not operating,
but is a versatile multi-purpose instrument taking full advantage of modern
technology. It combines a camera with a spectrograph and covers a wide
range of wavelengths from the near-infrared region into the ultraviolet.

COSTAR
COSTAR is not really a science instrument: it is the corrective optics
package that replaced the High Speed Photometer (HSP) during the first
servicing mission. COSTAR was designed to correct the effects of the
primary mirror's aberration.

NICMOS
The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) is an
instrument for near-infrared imaging and spectroscopic observations of
astronomical targets. NICMOS detects light with wavelengths between 800 and
2500 nanometres.

ACS
ACS is a so-called third generation Hubble instrument. Its wide field of
view is nearly twice that of Hubble's previous workhorse camera, WFPC2. The
name, Advanced Camera for Surveys, comes from its particular ability to map
relatively large areas of the sky in great detail.

Caption:

Hubble exposed

This cutaway view of Hubble shows the configuration of the telescope, the
instruments and the many other essential systems that allow it to point,
operate and communicate.

P25

Aperture door
Hubble's aperture door can be closed if Hubble is in danger of letting
light from the Sun, Earth or Moon into the telescope.

Secondary mirror
Like the primary mirror, Hubble's secondary mirror is made of special glass
coated with aluminium and a special compound to reflect ultraviolet light.
It is 1/3 metre in diameter and reflects the light back through a hole in
the primary mirror and into the instruments.

Solar panels
Hubble's third set of solar arrays produce enough power to enable all the
science instruments to operate simultaneously, thereby making Hubble even
more efficient. The panels are rigid and unlike earlier versions, do not
vibrate, making it possible to perform stable, pinpoint sharp observations.

Communication antennae
Once Hubble observes a celestial object, its onboard computers convert the
image or spectrum into long strings of numbers that, via one of Hubble's
two antennae, are sent to one of the two satellites that form the Tracking
and Data Relay Satellite System (TDRSS).

Support systems
Containing essential support systems such as computers, batteries,
gyroscopes, reaction wheels and electronics.

WFPC2
WFPC2 was Hubble's workhorse camera until the installation of ACS. It
records excellent quality images through a selection of 48 colour filters
covering a spectral range from far-ultraviolet to visible and near-infrared
wavelengths. WFPC2 has produced most of the stunning pictures that have
been released as public outreach images over the years.


P26

No single nation could undertake
such an enormous project

For astronomers, the most important components of Hubble are its scientific
instruments. There are two groups of instruments in Hubble, known as
'radial' - mounted around Hubble's waist; and 'axial' - fitted at the back
end of the spacecraft. The different instruments serve different purposes:
some are for making images and some are designed to dissect the light from
the stars and galaxies by spreading it out to form a rainbow-like spectrum.
Hubble's unique vantage point in space makes it capable of observing over a
broader band of wavelengths than ground-based (optical) telescopes. It can
observe ultraviolet light that is completely absorbed by Earth's
atmosphere. It can also see much more clearly in the near-infrared part of
the spectrum where the Earth's sky is very bright and not very transparent.
These forms of light reveal properties of celestial objects that are
otherwise hidden from us.
Some instruments, like ACS - the Advanced Camera for Surveys - are better
for visible and ultraviolet observations, some, like NICMOS - the Near
Infrared Camera and Multi-object Spectrograph - are designed for infrared
observations.
Different mechanical and electrical components keep Hubble functioning. The
power for Hubble comes from solar panels on the side that convert sunlight
into electricity. Gyroscopes, star trackers and reaction wheels keep Hubble
steady and pointing in the right direction for hours or days at a time: not
too close to the Sun, Moon or Earth as they would destroy the light-
sensitive instruments; and accurately towards the objects being studied.
The Hubble pointing and tracking system is a triumph of engineering and
relies on a complex hierarchy of systems that keep the entire spacecraft
stable in space to an almost incredible precision. It can point to the same
spot on the sky for weeks at a time without deviating by more than a few
millionths of the Moon's diameter.
Hubble has several communications antennae on its side that are used for
sending observations and other data down to Earth. Hubble sends its data
first to a satellite in the Tracking and Data Relay Satellite System, which
then downlinks the signal to White Sands, New Mexico, USA. The observations
are sent from NASA in the United States to Europe where they are stored in
a huge data archive in Munich, Germany.
No single nation could undertake such an enormous project. Hubble has been
a major collaboration between NASA and ESA, the European Space Agency, from
an early stage in its life. ESA has contributed an instrument, two sets of
Solar Arrays, various electronic systems and a substantial group of people
to the project.

P27

Hubble has been of paramount importance to European astronomy. European
astronomers regularly win more than 15 percent of the observing time with
Hubble, resulting in several thousand scientific publications over the
years. Much of the work done by astronomers with Hubble is complemented by
observations made with ground-based and other space telescopes.
Two groups of European specialists work with Hubble. There are 15 people
from ESA currently working at the Space Telescope Science Institute in the
USA, and 20 others make up the Space Telescope-European Coordinating
Facility in Munich, Germany.

Box:

Hubble facts

A few of the lesser known facts about Hubble are: it has orbited the Earth
more than 80 000 times and travelled nearly 4 billion kilometres - more
than 25 times the distance to the Sun. It has made 700 000 exposures of 22
000 different astronomical targets, producing 20 Terabytes of data that
have resulted in about 6 000 scientific papers - a very high number even
given the considerable outlay on the project.

Orbital altitude: 568 km
Orbital time: 96 minutes
Mission lifetime: 20 years
Exposures: approx. 700 000
Different objects observed: approx. 22 000
Data: more than 20 TB downloaded to Earth
Distance travelled: 80 000 times around the Earth (nearly 4 billion
kilometres)
Number of scientific papers: approx. 6 000
Angular resolution: 0.05 arc-seconds
Wavelength range: 110 - 2400 nm (from ultraviolet to near-infrared)
Mirror diameter: 2.4 m
Pointing stability: Hubble moves less than 0.007 arc-seconds in 24 hours
Costs: ESA's financial contribution over 20 years is 593 million Euros
Dimensions: 15.9 metres long, diameter 4.2 metres
Launch Date: 24 April, 1990, 12:33:51 UT
Weight: 11 110 kg

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3 Planetary Tales

Planetary systems are made up of material leftover from the formation of
their parent star. Astronomers expect the formation of 'debris disks' to be
a common result of star formation and so expect there to be many 'Solar
Systems' awaiting discovery: indeed, over the last few years, the first
hundred or so of these have already been found around nearby stars. Hubble
performs long-term studies of members of our Solar System and has made
unique observations of planets in others.

Caption:

A 'terrestrial' planet orbiting a sun-like star (artist's impression)

In contrast to the successful searches for massive gas giants like Jupiter,
finding small, Earthlike, rocky planets around other stars will be a very
difficult task. None have been found yet although experiments are being
planned to search for, and eventually to study, them. The goal is, of
course, to search for signs of habitation.

Credits: ESA

P30

We are just the leftovers
of our Sun's birth

There are no boundaries in space. In this vast Universe, our closest
relatives are the objects within the Solar System: we share the same origin
and the same destiny.
Our Solar System was formed about four and a half billion years ago from a
huge gas cloud. Ironically, it could have been the deadly force of a
thermonuclear blast from an exploding star in the vicinity that triggered
our creation. The devastating force of the blast may have disturbed the
precarious equilibrium of the original gas cloud, causing some of the
matter to collapse inwards and creating a new star, our Sun. A minute
percentage of the collapsing matter became the multifaceted assembly of
planets that we have around us today.
We are, in other words, just the leftovers of our Sun's birth. The planets
were born in the rotating disk of dust and gas left behind as our mother
star was formed. The rocky planets formed in the inner Solar System while
the enigmatic gas giants were formed further out. And then, when a fierce
wind of smashed atoms began to blow from the Sun - or perhaps from hot
nearby stars or a nearby supernova - only sizable planets could maintain
their gaseous surroundings and the last wisps of the tenuous cloud between
the planets was whipped away. So, in our Solar System's zoo of celestial
bodies there are both rocky worlds and giant gaseous planets.
Even now, there is no exact estimate of how much matter or even how many
planets exist within our Solar System. Since Pluto's discovery in the
1930s, and its satellite Charon's in the 1970s, astronomers have tried to
figure out if there is anything else out there beyond the ninth planet.
In 2003, Hubble spotted something moving fast enough across the background
of faraway stars to be an object within the Solar System. Estimates show
that it could be about the size of a planet and it has been named Sedna,
after an Inuit goddess. Sedna may be 1500 km in diameter - about three
quarters the size of Pluto, but it is so far away that it appears as just a
small cluster of pixels even to Hubble. Nevertheless, it is the largest
object discovered in the Solar System since Pluto. The Sun is about 15
billion km from Sedna - 100 times further than Earth's distance from the
Sun - and barely gives out as much light and heat as the full moon. So
Sedna is engulfed in an eternal bleak winter.
Sedna is not the only mysterious object out there. Debris from the
formation of the planets is still floating everywhere in the form of
asteroids and comets of various shapes and sizes. Sometimes their orbits
can lead them on catastrophic courses.

P31

Caption:

Comet impact

This true colour image of the giant planet Jupiter, taken with Hubble's
WFPC2 camera, reveals the impact sites of fragments 'D' and 'G' from Comet
Shoemaker-Levy 9.

Credits:

H. Hammel, MIT and NASA/ESA

P32

Credits:

NASA/ESA, J. Bell (Cornell U.), and M. Wolff (Space Science Inst.)

P33

Hubble has opened a window on our
Solar System that is never closed

Hubble is able to react quickly to dramatic events occurring within the
Solar System. This has allowed it to witness the dramatic plunge of comet
Shoemaker-Levy 9 into Jupiter's atmosphere. The comet was torn into
numerous pieces by Jupiter's gravitational pull when it passed the massive
planet in the summer of 1992. Two years later, these fragments returned and
drove straight into the heart of Jupiter's atmosphere.
Hubble followed the comet fragments on their last journey and delivered
stunning high-resolution images of the impact scars. Our Earth could easily
fit into any of these black bruises. The consequences of the impact could
be seen for days afterwards and, by studying the Hubble data, astronomers
were able to assemble fundamental information about the composition and
density of the giant planet's atmosphere.
Space probes with sophisticated instruments are frequently sent to the
planets of our Solar System. They provide close-up investigations of these
distant places. While a few go into orbit around their destination planets
and so can monitor them for long periods, most fly by quickly and gather
some snapshots on the way. Although Hubble's high resolution images can be
surpassed by close-up pictures taken by planetary space probes, Hubble has
the advantage of being able to carry out long-term monitoring. This is
crucial for the study of planetary atmospheres and geology. Weather systems
can reveal much about underlying atmospheric processes.
Hubble provides its own unique service, by opening a window on our Solar
System that is never closed. It can be used to monitor almost any planet in
the Solar System (Mercury is too close to the Sun) regularly and to provide
a long-term view of changes that is impossible to achieve in any other way.
This is how we see developing storms on other planets; their changing
seasons; and unprecedented views of other atmospheric events, such as
aurorae, known on Earth as the northern and southern lights.
Hubble's extremely high resolution and sensitivity have resulted in unique
observations of objects within the Solar System, providing amazing images
and rich streams of data about the nature of these bodies. Hubble has seen
unprecedented detail in Jupiter's aurorae: while similar to those seen
above the Earth's polar regions, they are almost 1000 times more energetic
and much more complex. Jupiter's aurorae can only be seen in ultraviolet
light and, so they can never be studied with ground-based telescopes.
Astonishing images of Saturn's aurorae have also been taken and reveal that
the glowing curtains of ultraviolet light rise more than a thousand
kilometres above the cloud tops of the planet's north and south poles.

Caption:

Mars up close

This view of Mars, the sharpest photo of it ever taken from the vicinity of
Earth, reveals small craters and other surface markings only a few tens of
kilometers across. The Advanced Camera for Surveys (ACS) aboard Hubble took
this image on the 24th August 2003, just a few days before the red planet's
historic 'close encounter' with Earth.

P34

Glowing curtains of ultraviolet light
that rise more than a thousand
kilometres above the cloud tops

credits Saturn:

NASA, ESA, J. Clarke (Boston University, USA), and Z. Levay (STScI)

P35

Even though the solar system clearly has many more surprises in store for
us, Hubble has also turned its eye out towards other stars, looking for
planetary systems. Astronomers are beginning their search for life
elsewhere in the Universe. The primary objective is to find earth-like
planets. These are very much harder to detect than massive 'Jupiters' and,
as yet, none have been found.
Hubble had been in orbit for five years when the first planet around a Sun-
like star was discovered. Although it was not designed to study these
objects, Hubble's versatility has allowed it to make significant
contributions to this intensely interesting area of study. For example,
Hubble's high resolution has been indispensable in the investigation of the
gas and dust disks, dubbed 'proplyds', around the newly born stars in the
Orion Nebula. The proplyds may very well be young planetary systems in the
early stages of creation. The details revealed by Hubble are superior to
anything seen to date with ground-based instruments and, thanks to Hubble's
capability, we now have visual proof that dusty disks around young stars
are common.
Hubble has also measured the mass of a planet - only the second time such a
calculation has been performed with any accuracy - by detecting the way in
which the planet causes its star to wobble. Hubble found the oldest planet
so far known: it orbits a tiny stellar husk, which was once a blazing star
like the Sun, and is located 5,600 light years away. The planet was once
like Jupiter and is around 13 billion years old, almost three times older
than our own planetary system.

Caption Jupiter:

Io's shadow cast on Jupiter

Jupiter's volcanic moon Io zips around Jupiter every 1.8 days. Here,
Hubble's WFPC2 captures the 3,640 km diameter moon casting its black shadow
on the giant planet.

Caption Saturn:

Saturn's aurora

Astronomers combined ultraviolet images of Saturn's southern polar region
with visible-light images of the planet and its rings to make this picture.
The auroral display appears blue because of the glow of ultraviolet light.
In reality, the aurora would appear red to an observer at Saturn because of
the presence of glowing hydrogen in the atmosphere. The ultraviolet image
was taken on 28 January 2004 by Hubble's Imaging Spectrograph (STIS). The
ACS was used on 22 March 2004 to take the visible-light image.

Credits Jupiter:

J. Spencer (Lowell Observatory) and NASA/ESA

P36

One day we will search for the
markers of life beyond Earth

With ground-based telescopes, the gas giant planet HD 209458b, 150 light-
years from Earth, was discovered in 1999 through its slight gravitational
tug on its 'mother-star'. In 2001 Hubble made highly accurate measurements
of the dip in the star's light when the planet passed in front. The first
detection of an atmosphere around an extrasolar planet was also made in
this object. The presence of sodium as well as evaporating hydrogen, oxygen
and carbon was detected in light filtered through the planet's atmosphere
as it passed in front of the star.
Measuring the chemical makeup of extra-solar planetary atmospheres will one
day allow us to search for the markers of life beyond Earth. All living
things breathe and this changes the composition of the atmosphere in
readily detectable ways. Light-harvesting plants will impose their own
colourful 'biomarkers' on the light reflected from planetary surfaces.
Astronomers believe there are many planetary systems similar to ours
orbiting other stars throughout the Galaxy. The birth, life, death and
rebirth of stars continues in an unending cycle in which stars, born of gas
and dust, will shine for millions or billions of years, die and return as
gas and dust to form new stars. The by-products of this continual process
include planets and the chemical elements that make life possible.
And so, through the entire vastness of space, the eternal ebb and flow of
life continues.

P37

Caption:

Transiting exoplanet

This artist's impression shows the planet HD 209458b transiting its parent
star. Hubble's spectrometer STIS has been used to detect - for the first
time - the signature of the giant planet's atmosphere evaporating off into
space. Astronomers call HD 209458b a 'hot Jupiter' because it orbits much
closer to its star than our own planet of that name.

Credits:

ESA

P39

4 The Lives of Stars

The Sun is a typical star amongst the 100 billion or so in our Milky Way
galaxy. Some are more massive - living relatively brief and spectacularly
brilliant lives; some are less so and can live longer than the present age
of the Universe. Stars are chemical factories, constructing the elements
from which we and the Earth are made: most of the atoms in the newly-formed
Universe were hydrogen and helium and the stars had to convert this raw
material into what we need for life. Some short-lived phases of a star's
evolution have produced the most remarkably beautiful structures that
Hubble has ever imaged.

Caption:

M17 in Sagittarius

This WFPC2 image, taken in the light of glowing hydrogen (green), oxygen
(blue) and sulphur (red), shows a small region within the star-forming
Omega or Swan nebula. The wave-like patterns of gas have been sculpted and
illuminated by a torrent of ultraviolet radiation from young, massive stars
that lie outside the picture to the upper right.

Credits:

European Space Agency, NASA, and J. Hester (Arizona State University)

P40

Credits:

Jeff Hester and Paul Scowen (Arizona State University), and NASA/ESA

P41

A star is a sphere of glowing gas

Our Sun, that vital source of energy for life on Earth, is a star. A
totally unexceptional star, just like billions of others that we can find
throughout the Galaxy.
A star is a sphere of glowing gas. It forms out of a cloud of gas
compressed by gravity and releases energy steadily, throughout its life,
because a chain of nuclear reactions is continuously taking place in its
core. Most stars combine hydrogen atoms to form helium through the process
called nuclear fusion; the same process that powers a devastating hydrogen
bomb. In fact, stars are nuclear factories that convert lighter elements
into heavier elements in a series of fusion reactions. They will keep
glowing until they run out of 'fuel'. And that's it; a star's life; a quiet
beginning and a steady progress to a sometimes violent end. But how can we
be certain of this picture when an individual star like the Sun outlives
humans by a factor of a few hundred million?
To investigate the lifecycle of a particular organism on Earth, we don't
have to track an individual specimen's entire life. Instead, we can observe
many of the organisms at once. This will show us all the different phases
of its life cycle. For example, each stage of a person's life is a snapshot
of the human experience. And so it is with stars.
Stars live and die over millions, or even billions, of years. Even the most
reckless stars live for at least one million years; longer than the entire
history of mankind! And this is why it is extremely unusual to be able to
track age-related changes in individual stars.
To learn more about stars, we must sample different stars at every stage of
life and piece together the whole cycle from birth to death. Hubble's vivid
images have documented the tumultuous birth of stars and delivered many
astonishing pictures documenting their evolution. The birth of stars in
neighbouring stellar 'maternity wards' can be used as a time machine to
replay the events that created our Solar System.
Hubble has gone beyond what can be achieved with other observatories by
linking together studies of the births, lives and deaths of individual
stars with theories of stellar evolution. In particular, Hubble's ability
to probe individual stars in other galaxies enables scientists to
investigate the influence of different environments on the lives of stars.
These are crucial data that allow us to extend our understanding of the
Milky Way to other galaxies.

Caption

Pillars of creation

This image, taken with WFPC2 in 1995, has become a universally recognised
icon. Part of M16, the Eagle nebula, these Evaporating Gaseous Globules
(EGGs) are protrusions of cool, dusty, molecular gas into hotter, more
tenuous material excited by young, hot stars in this nearby star-forming
region.

Cosmic recycling

Lighter elements such as carbon, nitrogen, oxygen, silicon are made as a
result of fusion reactions taking place in stars. The heavier elements,
however, are built during the cataclysmic stellar explosions we know as
supernovae. When the Universe was very young - before any stars and
galaxies had formed - hydrogen and helium were overwhelmingly its dominant
atomic constituents.

P42

Caption:

Colourful Tarantula

The Tarantula nebula is situated 170,000 light-years away in the Large
Magellanic Cloud (LMC), visible to the naked eye in the Southern sky.
Supernovae have already detonated in this huge star-forming region and the
resulting blast waves have compressed the gas into filaments and sheets.
This mosaic of images was created using Hubble archival data by 23 year old
amateur astronomer, Danny LaCrue. It was constructed from 15 individual
exposures taken through three narrow-band filters.

Credits:

ESA/NASA, ESO and Danny LaCrue

P44

Credits:

C.R. O'Dell (Rice University), and NASA/ESA

Caption:

Hubble's view of Orion

This spectacular colour panorama of the centre of the Orion Nebula is one
of the largest pictures ever assembled from individual images taken with
the Hubble telescope. The richly detailed tapestry revealed by Hubble shows
a churning, turbulent star factory set within a maelstrom of flowing,
luminescent gas. Though this 2.5-light-year-wide view is but a small
portion of the entire nebula, it includes a star cluster and almost all of
the light from the bright glowing clouds of gas that make up the nebula.

P45

Important clues about our genesis
lie hidden behind the veil of gently
glowing, dust-laden molecular clouds

Hubble has often had to work hard for this information because these
important clues about our genesis lie hidden behind the veil of gently
glowing, dust-laden molecular clouds where stars are formed.
There are stars forming throughout the Universe. Enormous glowing pillars
of dusty hydrogen gas stand sentinel over their cradles, basking in the
light of nearby, newly-formed stars.
Hubble's ability to observe infrared light enables it to penetrate the dust
and gas and reveal the newly born stars as never before.
One of the most exciting of Hubble's many discoveries was the observation
of dust disks surrounding some newborn stars, buried deep inside the Orion
Nebula. Here we are actually seeing the creation of new solar systems where
planets will eventually form; just as they did in our own Solar System four
and a half billion years ago.
In the first stages of their lives, stars can stock up on gas from their
original birth cloud. Material falling into the star creates bubbles or
even jets as it is heated and blasted along a path that follows the star's
rotation axis, like an axle through a wheel.
Often many stars are born from the same cloud of gas and dust. Some may
stay together through their whole lifetime, keeping step as they evolve,
like the childhood friends that you keep for life.

Caption:

Proto-Solar Systems?

Disks around young stars (also known as circumstellar or protoplanetary
disks) are thought to be made up of 99% gas and 1% dust. Even that small
amount of dust is enough to make the disks opaque and dark at visible
wavelengths. These dark disks are seen here because they are silhouetted
against the bright backdrop of the hot gas of the Orion nebula.

Credits:

Mark McCaughrean (Max-Planck-Institute for Astronomy), C. Robert O'Dell
(Rice University), and NASA/ESA

P47

Caption:

The Carina Nebula

Previously unseen details of a mysterious, complex structure within the
Carina Nebula (NGC 3372) are revealed by this image of the 'Keyhole
Nebula', obtained using four different pointings of the WFPC2 camera
through six colour filters. The picture is dominated by a large,
approximately circular feature, which is part of the Keyhole Nebula, named
in the 19th century by Sir John Herschel. This region, about 8000 light-
years from Earth, is located adjacent to the famous explosive variable star
Eta Carinae, which lies just outside the field of view toward the upper
right. The Carina Nebula also contains several other stars that are among
the hottest and most massive known, each about 10 times as hot, and 100
times as massive, as our Sun.


Credits:

NASA/ESA, The Hubble Heritage Team (AURA/STScI)

P48

Human existence is the mere blink of an eye
compared with the life of a star

The stars in a cluster will all have the same age, but will have a range of
different masses. And this means that very different destinies await them.
Human existence is the mere blink of an eye compared with the life of a
star, so the direct observation of a transition between the different
stages of a star's life can only come about by lucky chance. Hubble uses
its stability and exceptionally sharp focus to

Caption:

Young star's jet

This view of a 5 trillion kilometre long jet called HH-47 reveals a very
complicated jet pattern which indicates the star (hidden inside a dust
cloud near the left edge of the image) might be wobbling, possibly caused
by the gravitational pull of a companion star.

Credits:

J. Morse/STScI, and NASA/ESA

P49

reveal changes on cosmic scales over periods of only a few years. From the
ground it is usually not possible to see this kind of evolution taking
place over such short periods. In the Universe, this sort of action
normally takes place on timescales of many thousands or even millions of
years, so being able to follow real time changes in astronomical objects is
a considerable asset.
At the other extreme of the stellar life cycle, Hubble has monitored
Supernova 1987A since 1991, four years after it exploded. The result is a
series of stunning observations that show the evolution following the
violent explosion witnessed nearly two decades ago.
The regular monitoring of an even older supernova remnant, the Crab Nebula,
has enabled Hubble to capture the display of matter and antimatter
particles propelled close to lightspeed by the Crab pulsar, a rapidly
rotating neutron star. Thanks to Hubble, scientists can directly follow the
motion of the gas remnant left behind by the supernova explosion witnessed
by Chinese astronomers in 1054.
Not all elderly stars end their lives as supernovae and Hubble has followed
the final stages of their lives, with their very different outcomes. One
such elderly star V838 Monocerotis, located about 20,000 light-years from
Earth put out a brief flash of energy that illuminated the surrounding
dust. The progress of the light echo across the dust was captured by Hubble
in a film-like sequence of unprecedented clarity.
The stars containing the most mass end their lives cataclysmically,
destroying themselves in titanic stellar explosions known as supernovae.
For a few glorious months, each becomes one of the brightest objects in the
entire Universe, outshining all the other stars in its parent galaxy.
Since its launch in 1990, Hubble has watched the drama unfold in Supernova
1987A, the nearest exploding star in modern times. The telescope has been
monitoring a ring of gas surrounding the supernova blast.
Hubble has observed the appearance of bright spots along the ring, like
gemstones on a necklace. These cosmic 'pearls' are now being lit by
supersonic shocks unleashed during the explosion of the star.
The ruins of an exploding star can hide a powerful engine. Hubble has
probed the mysterious heart of the Crab Nebula, the tattered remains of an
exploding star, vividly described by Chinese astronomers in 1054, and has
revealed its dynamic centre. The innermost region of this nebula harbours a
special type of star, a pulsar. This star rotates like a beacon, emitting
light and energy in a beam. And it energizes and illuminates the vast
nebula of dust and gas surrounding it.

P50

Caption:

Light echo movie

In fifteen highly productive years, Hubble has allowed us to observe some
stars ageing in real time. The telescope has produced startling 'movies'
that allow us to witness how some of them do modify their appearance over
this minute span of astronomical time.

Caption:

The Crab Nebula

Much of the light emitted by an object like the Crab Nebula comes from what
astronomers call a 'non-thermal' process. Electrons, travelling at speeds
close to that of light, spiral around lines of magnetic field and so
produce radiation covering the entire electromagnetic spectrum, from X-rays
to radio waves. This is why the pictures of the Crab taken in X-rays and
optical light look so similar. This is a composite image of the Crab Nebula
showing the X-rays (blue), and optical (red) radiation.

Credits:

NASA/ESA/ASU/J. Hester et al.

P51

Caption:

V838 Monocerotis

Some of the most impressive celestial 'movies' are created by pulses of
light travelling out from a stellar explosion like a flash from a camera.
As the 'sphere of light' expands away from its origin, it can illuminate
surrounding material to produce what we call 'light-echoes'. These produce
the illusion of material in rapid motion while, in reality, it is the pulse
of light that is moving.

Credits:

NASA, the Hubble Heritage Team (AURA/STScI) and ESA

P52

Credits:

Nordic Optical Telescope and Romano Corradi (Isaac Newton Group of
Telescopes, Spain)

P53

The Sun will swallow Mercury, Venus
and our planet as well

However, not all stars end their lives so violently. Sun-like stars cool
down once they run out of hydrogen. The centre collapses in on itself and
the heavier elements are burnt, causing the outer layers to expand and leak
slowly into space. At this stage in a star's life, it is called a "red
giant".
Our Sun will become a "red giant" in a few billion years. At that time, it
will expand so much that it will swallow Mercury, Venus and our planet as
well.
But these stars are not finished quite yet. They can still evolve into
something extraordinary. Just before they breathe their last breath, stars
like our Sun go out in a final blaze of glory.
In its final stages of nuclear fusion, stellar winds blow from the star,
causing the remnants of the red giant to swell to an enormous size. At the
heart of this expansion, the exposed heart of the star, an intensely hot
dwarf, floods the gaseous envelope with powerful ultraviolet light, making
it glow in a whole range of beautiful colours.

Caption for p52

Wide angle Cat's Eye

Wide angle view of the enormous but extremely faint halo of gaseous
material surrounding the Cat's Eye Nebula showing material ejected during
earlier active episodes in the star's evolution. This probably happened
some 50,000 to 90,000 years ago.:

Caption on p 53

Hubble's close up view of the Cat's
Eye

Detailed view from Hubble focussing on central regions of the Cat's Eye
Nebula seen on the previous page. Although this nebula was among the first
planetary nebula ever to be discovered, it is one of the most complex
planetary nebulae ever seen in space. A planetary nebula forms when Sun-
like stars gently eject their outer gaseous layers to form bright nebulae
with amazing twisted shapes.

Credits:

ESA, NASA, HEIC and The Hubble Heritage Team (STScI/AURA)

P54

Since these amazing constructions looked a bit like the newly discovered
planet Uranus to early telescopic astronomers, they became known as
planetary nebulae. From telescopes on Earth they look like round (planet-
shaped) objects with fairly simple geometries. Hubble's keen perception
shows that each planetary nebula is a distinct individual. How a normal Sun-
like star evolves from a relatively featureless gas sphere to a nebula with
intricate glowing patterns is still one of the unsolved mysteries in
astronomy. Each additional image of the glowing patterns of gas intrigues
astronomers anew.
From its unique position high above the distorting atmosphere Hubble is the
only telescope that can observe the swollen outer envelope of these dying
stars in full detail.
Hubble has been able to observe the expansion of the nebula itself
directly. The Cat's Eye Nebula, for instance, has been observed with Hubble
over a period of eight years and is a marvellous example of the resolving
power of the telescope.

Box:

Colours of Planetary Nebulae

The intensely hot stars at the centres of planetary nebulae flood the
surrounding volume of gas with ultraviolet light. This causes the atoms in
the gas to lose one or more of their electrons. The resulting 'ions'
radiate their energy away in a series of discrete colours that astronomers
can observe to measure gaseous temperatures, densities, chemical
composition and motions.

Caption:

A Collection of Planetary Nebulae
Hubble's dazzling collection of planetary nebulae show surprisingly
intricate, glowing patterns: sprinkling jets, pinwheels, ghostly filaments,
supersonic shocks, concentric rings and intricate tendrils of gas and fiery
lobes. With their gauzy symmetrical wings of gas they resemble butterflies.

Credits:

ESA

P55

One of the greatest mysteries in modern
astrophysics is how a simple, spherical gas
ball can give rise to these intricate structures!

One of the greatest mysteries in modern astrophysics is how a simple,
spherical gas ball such as our Sun can give rise to these intricate
structures!
For some planetary nebulae it is as if a cosmic garden sprinkler created
the jets that stream out in opposite directions; or could these amazing
patterns possibly be sculpted by the magnetic field of a companion star
that funnels the emitted gas into a jet?
Whatever their cause, in only ten thousand years these fleeting cosmic
flowers disperse in space. Just as real flowers fertilize their
surroundings as they decompose, the chemical elements produced inside the
star during its life are dispersed by the planetary nebula to nourish the
space around it, providing the raw material for new generations of stars,
planets and possibly even life.
Because they disappear so quickly on a cosmic timescale there are never
more than about 15,000 planetary nebulae at any one time in our Milky Way.
A more lasting monument to the dead star is the tiny heart it leaves
behind. Known as a white dwarf, each of these exceptionally dense, Earth-
sized stars are fated to spend the rest of eternity gradually leaking their
residual heat into space, until eventually, in many billions of years, they
approach the frigid -270њC of space. Hubble was the first telescope to
observe white dwarfs in globular star clusters directly. White dwarfs
provide a 'fossil' record of their progenitor stars that once shone so
brightly that they long ago exhausted their nuclear fuel. These
measurements make it possible to determine the ages of these ancient
clusters - a critical cosmological datum for astronomers.

Caption:

IC 4406, the Retina nebula

Hubble reveals a rainbow of colours in this dying star, called IC 4406.
Like many other so-called planetary nebulae, IC 4406 exhibits a high degree
of symmetry. The nebula's left and right halves are nearly mirror images of
one another. If we could fly around IC 4406 in a spaceship, we would see
that the gas and dust form a vast doughnut of material streaming outward
from the dying star.

Credits:

NASA/ESA and The Hubble Heritage Team (STScI/AURA)

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Caption:

The Double Cluster NGC 1850

Found in one of our neighbouring galaxies, the Large Magellanic Cloud
(LMC), this young globular-like star cluster is an eye-catching object. NGC
1850 is a type of object unknown in our own Milky Way galaxy and is
surrounded by a pattern of filamentary nebulosity thought to have been
created during supernova blasts.

Credits:

ESA, NASA and Martino Romaniello (European Southern Observatory, Germany)

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5 Cosmic Collisions

On the hundred thousand light-year scale of a galaxy, stars are minute
particles. During the long history of the Universe, many galaxies have
collided and sometimes merged with one another, but huge interstellar
distances mean that a direct collision between two stars is highly
unlikely. However, the gas and dust drifting in interstellar space does
interact strongly, producing shocks and triggering firework displays of
starbirth. Computer simulations of colliding galaxies create a ballet of
shape and motion that show the slow, majestic workings of gravity.

Caption:

The core of the Antennae

Orange blobs, left and right of image centre, crisscrossed by filaments of
dark dust are the nuclei of twin galaxies. A wide band of chaotic dust,
called the overlap region, stretches between them. Sweeping spiral-like
patterns, traced by bright blue star clusters, show the result of a
firestorm of star birth activity that was triggered by this monster
collision of galaxies. This is a WFPC2 image released in 1997.

Credits: Brad Whitmore (STScI), and NASA/ESA

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We live inside a huge star system,
or galaxy, known as the Milky Way

We live inside a huge star system, or galaxy, known as the Milky Way. Seen
from outside, the Milky Way is a gigantic spiral, consisting of a central
hub embraced by long arms. The whole system slowly rotates. Between the
stars are vast amounts of gas and dust - that we can see - and some unknown
material called 'Dark Matter' that is invisible to us.
Far from the centre, out in one of the arms, the outer suburbs of the Milky
Way, is a tiny star system, our home, the Solar System. When we look up on
a clear night, we can see about 5000 of the brightest stars. Most of these
are our closest neighbours, but a few are more distant and appear bright
because of their great luminosity.
Our eyes struggle to see beyond a thousand light-years because of the dust
that blankets space and dims the distant starlight. So without a telescope
we can only see a minute portion of the entire 100,000-light-year-wide
Milky Way. For the Milky Way contains several hundred billion stars, many
like our own Sun! Although several hundred thousand million is an almost
unfathomable number, it is only the beginning. Astronomers believe there
are more than a hundred billion galaxies in the Universe. How many stars
would that be?
In a handful of sand there can easily be 50,000 individual grains of sand.
Even so, on an entire beach there are only just enough grains of sand to
represent each star in the Milky Way. There are so many stars in the
Universe that we would need to count every grain of sand on every beach on
the entire Earth to get anywhere near the right number!

Caption:

Ring galaxy AM 0644-741

Resembling a diamond-encrusted bracelet, a ring of brilliant blue star
clusters wraps around the yellowish nucleus of what was once a normal
spiral galaxy. The sparkling blue ring is 150,000 light-years in diameter,
making it larger than our entire home galaxy, the Milky Way. The galaxy,
catalogued as AM 0644-741, is a member of the class of so-called 'ring
galaxies'. Ring galaxies are an especially striking example of how
collisions between galaxies can dramatically change their structure, while
also triggering the formation of new stars. They arise from a particular
type of collision, in which one galaxy plunges directly through the disk of
another one. The ring is continuously forming massive, young, hot stars,
which are blue in color. Another sign of robust star formation is the pink
regions along the ring. These are rarefied clouds of glowing hydrogen gas,
fluorescing because of the strong ultraviolet light from the newly formed
massive stars.

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Credits:

NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

P63

Our life spans are nothing but brief drops
in the universal ocean of time

Let's take a grain of sand, 1 mm across, and place it to represent the size
of the Sun. If we started walking towards the nearest star it would take us
the better part of a day to complete the journey because the star would be
nearly 30 kilometres away.
So, galaxies are mostly large collections of emptiness. If we could squeeze
together all the stars in the Milky Way, they would easily fit into the
volume of space between our Sun and the nearest star. In fact, to
completely fill that volume, we would have to pack in all the stars from
all the galaxies in the entire Universe!
When looking at the night sky, the Universe seems motionless. This is
because our life spans are nothing but brief drops in the universal ocean
of time. In fact, the Universe is in constant motion, but we would need to
watch for vastly longer than a lifetime to perceive that motion in the
night sky.
Given enough time, we would see stars and galaxies move. Stars orbit the
centre of the Milky Way and galaxies are pulled together by each other's
gravity. Sometimes they even collide. Hubble has observed numerous galaxies
crashing together.
Hubble's beautiful images of galaxies excite us for many reasons. The
whirlpool forms, pastel colours of stellar and nebular light and dark
contrasting dust lanes are aesthetically pleasing, but the immense scale in
space and time that these vast islands of stars represent also leaves us
awestruck. The intricate patterns in spiral galaxies and especially those
systems of galaxies that are apparently interacting evoke a complex dynamic
Universe. Hubble's pictures alas are just snapshots capturing a single
moment in a slow evolution that lasts much longer than our puny human
lifetimes.

Box:

What do the colours of the galaxies mean?

Most of the Hubble galaxy images in this book are constructed to represent
approximately 'true' colour. Most of the light is coming from shining
stars. The relatively rare massive stars are hot and blue and so bright
that, in spite of their relatively small numbers, they contribute a
substantial part of the total light. These massive stars are short-lived
and are found in stellar nurseries shrouded in gas and dust. The
ultraviolet light from them excites the gas and makes it glow brightly in
several discrete colours, most notably the red of hydrogen and the green of
oxygen. Less massive - and more numerous - stars shine with pastel shades
from blue-white to orange-red, depending on their temperature, which in
turn depends on their mass. The palette is completed by the effects of
dust. Light shining through the clouds of dust is dimmed and reddened, a
little like the setting sun. We generally see this as a rather dirty brown
tint associated particularly with the stellar nurseries.

Caption:

Celestial Tadpole

Set against a stunning backdrop of thousands of galaxies, this odd-looking
galaxy with the long streamer of stars appears to be racing through space,
like a runaway pinwheel firework. This picture of the galaxy UGC 10214 was
taken in April 2002 by the Advanced Camera for Surveys (ACS), installed on
Hubble in March 2002 during Servicing Mission 3B. The faint, small
background galaxies in the picture stretch back to nearly the beginning of
time. They have a myriad of shapes and represent early samples of the
Universe's 13-billion-year evolution.

Credits:

NASA, Holland Ford (JHU), the ACS Science Team and ESA

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Credits:

NASA, Holland Ford (JHU), the ACS Science Team and ESA

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Caption:

The Mice

Located 300 million light-years away in the constellation Coma Berenices,
these colliding galaxies have been nicknamed 'the Mice' because of the long
tails of stars and gas emanating from each galaxy. Otherwise known as NGC
4676, the pair will eventually merge into a single giant galaxy.

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Like majestic ships in the grandest night,
galaxies can slip ever closer until their mutual
gravitational interaction begins to mould
them into intricate figures that are finally,
and irreversibly, woven together

Like majestic ships in the grandest night, galaxies can slip ever closer
until their mutual gravitational interaction begins to mould them into
intricate figures that are finally, and irreversibly, woven together. It is
an immense cosmic dance, choreographed by gravity. When two galaxies
collide, it's not like a car crash or two billiard balls hitting each
other, it is more like interlocking your fingers. Most of the stars in the
galaxies will pass unharmed through the collision. The chance of two stars
actually colliding is miniscule, so vast are the distances between them.
At worst, gravity will fling them out, along with dust and gas to create
long streamers that stretch a hundred thousand light-years or more. The two
galaxies, trapped in their deadly gravitational embrace, will continue to
orbit each other, ripping out more gas and stars to add to the tails.
Eventually, hundreds of millions of years afterwards, the two galaxies will
settle into a single, combined galaxy.
It is believed that many present-day galaxies, including the Milky Way,
were assembled from such a coalescence of smaller galaxies, occurring over
billions of years.
Triggered by the colossal and violent interaction between the galaxies,
stars form from large clouds of gas in firework bursts, creating brilliant
blue star clusters.
Our own Milky Way is on a collision course with the nearest large galaxy,
the Andromeda galaxy. They are approaching each other at almost 500,000
kilometres per hour and, in three billion years, will collide head-on. The
direct collision will lead to a magnificent

Caption:

Andromeda galaxy and the Milky Way collision

Seen from the Earth the collision between the Andromeda galaxy and the
Milky Way in three billion years will look something like this.

Credits:

John Dubinsky

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It is an immense cosmic dance,
choreographed by gravity

merger between the two galaxies, during which the Milky Way will no longer
be the spiral galaxy we are familiar with. Instead, it will evolve into a
huge elliptical galaxy, containing its own stars and those of the Andromeda
galaxy as well.
Although this will not happen for a very long time, there are other dark
forces of nature in play everywhere around us.

Caption:

Galaxies in close embrace

Modern computer simulations of colliding galaxies reveal the intricate
patterns of stellar orbits as gravity plays its part in the grand
evolutionary scheme of the Universe.

Credits:

John Dubinsky

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Credits:

NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

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Caption:

Dust and red star clusters in NGC 1316

Surprisingly complex loops and blobs of cosmic dust pervade in the giant
elliptical galaxy NGC 1316. NGC 1316's violent history is evident in
various ways. The inner regions of the galaxy shown in the Hubble image
reveal a complicated system of dust lanes and patches. These are thought to
be the remains of the interstellar medium associated with one or more of
the spiral galaxies it swallowed. Scattered around the galaxy, the red star
clusters provide clear evidence of a major collision of two spiral galaxies
that merged together a few billion years ago.

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Credits:

ESA

P71

6 Monsters in Space

Black holes are formed when gravity overwhelms all the other forces that
shape matter. They are found as remnants of massive stars and, in even more
massive versions, at the centres of most - if not all - galaxies. They are
fascinating objects with weird properties and impose their influence on the
surrounding matter and light. The most spectacular manifestations of such
supermassive black holes are quasars. Matter pours into a vast black hole
at a galactic core and this accretion results in a brightness that far
exceeds the sum of all the hundreds of billions of individual stars that
constitute the host galaxy.

Caption:

Doughnuts and supermassive black
holes

This artist's impression shows the dust torus around a supermassive black
hole. Black holes lurk at the centres of active galaxies in environments
not unlike those found in violent tornadoes on Earth. Just as in a tornado,
where debris is found spinning about the vortex, so, in a black hole, a
dust torus surrounds its waist. In some cases astronomers can look along
the axis of the dust torus from above or below and have a clear view of the
black hole. Technically these objects are then called 'type 1 sources'.
'Type 2 sources' lie with the dust torus edge-on as viewed from Earth so
that our view of the black hole is totally blocked by dust over a range of
wavelengths from the near-infrared to soft X-rays.

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There is no way to find out what is in
there. Not even light can escape. So how
do we know that they are even there?

Although the existence of black holes has been hypothesized for more than
200 years, a central tenet of the theory is that a black hole will be
impossible to observe directly. X-ray satellites had hinted that black
holes existed by detecting the emission of X-rays from superheated gas as
it was consumed by the black hole. Then, along came Hubble: its high
resolution made it possible to see the gravitational effects on matter
surrounding the largest black holes in the Universe. Hubble has also shown
that a black hole is most likely to be present at the centres of most
galaxies. This has important implications for theories of galaxy formation
and evolution since it implies that the black hole could be the 'seed' that
triggers a galaxy's formation.
Black holes are the enigmatic villains of the Universe: swallowing all that
comes their way and allowing nothing to escape from within their
gravitational stronghold. There is no way to find out what is in there. Not
even light can escape. So how do we know that they are even there?
Black holes themselves cannot be observed directly. However, astronomers
can study the indirect effects of black holes because the one thing they
have in abundance is gravity.
Astronomers believe that black holes are singularities - simple points in
space. No volume, no extension, but infinitely dense, black holes can be
created during the final collapse of a massive star, many times the size of
the Sun.
The stellar corpse left over from the demise and collapse of a massive star
can be so heavy that no force in nature can keep it from crumpling under
its own weight into an infinitely small volume. Although the matter has
apparently disappeared, having been compacted into nothingness, it still
exerts a powerful gravitational pull and stars and other objects that come
too close can be pulled in.
For any black hole there is a point of no-return, called the "event
horizon". Once something - a nearby star say - is pulled in past this point
it will never be seen again. On its way towards the event horizon, the
doomed star will begin to follow a fatal, spiralling orbit.
As the star approaches the black hole still further, the matter closest to
the hole feels a greater attraction than the rest of the star, sucking and
stretching the star out towards the hole until the immense tidal forces
pull it to pieces and devour it.
There are quirkier aspects to these objects too, a twisting of space and
time that warps and slows even the passage of time. All objects with a mass
deform the very fabric of space and time, but black holes do this to an
extreme degree.

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Caption:

Black Eye Galaxy

A relic of two colliding galaxies, the merged star system, Messier 64 has a
spectacular dark band of absorbing dust in front of the galaxy's bright
nucleus, giving rise to its nickname the 'Black Eye Galaxy'. Fine details
of the dark band are revealed in this image of the central portion of
Messier 64 obtained with the Hubble Space Telescope. Hubble has found that
black holes reside at the centre of most galaxies, such as the Black Eye
Galaxy.

Credits:

NASA/ESA and The Hubble Heritage Team (AURA/STScI)

P74

A wormhole is essentially a
'shortcut' through spacetime

According to Einstein's famous Theory of General Relativity, an intrepid
traveller who could visit a black hole and hang above the event horizon
without being swallowed would eventually return to find himself younger
than the people he had left behind.
Perhaps the most curious objects astronomers have hypothesized about are
wormholes. A wormhole is essentially a 'shortcut' through spacetime from
one point in the Universe to another point in the Universe. Maybe
wormholes, if they exist, will some day allow travel between regions in
space faster than it would take light to make the journey through normal
space.
Hubble's high resolution has revealed the dramatic distorting effects of
black holes on their surroundings. Hubble has shown that black holes are
most likely to be present at the centre of most galaxies. There is one at
the centre of our Milky Way - a giant, super-massive black hole, perhaps a
million times bigger than those created from the collapse of massive stars.
It may have shone much more brightly in the past, making the Galaxy appear
very active. This may happen again in the future: we know that such objects
can wax and wane over thousands or millions of years.
Our black hole could be the result of the merger of many star-sized black
holes that were formed during the remote history of the galaxy. When two
galaxies collide, the black holes at each of their centres will perform an
elaborate dance. Long after the two galaxies have merged into one, their
central black holes continue to orbit each other for hundreds of millions
of years before their final violent merger into a single, weighty black
hole. This final process is so powerful that it changes the fabric of
spacetime enough that we may be able to observe it from the Earth with a
new breed of gravitational-wave telescopes or from special spacecraft in
orbit.

Caption:

Disks around supermassive black holes

Two active galactic cores, NGC 7052 and NGC 4261 reveal their waist-
girdling disks of gas and dust to WFPC2 on Hubble. This material is the
reservoir of fuel that powers the quasar.

Credits:

Roeland P. van der Marel (STScI),
Frank C. van den Bosch (Univ. of Washington), and NASA/ESA

Credits:

L. Ferrarese (Johns Hopkins University) and NASA/ESA

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Caption:

Wormhole in space (artist's impression)

Perhaps the most curious objects astronomers have hypothesized about are
wormholes. A wormhole is essentially a 'shortcut' through spacetime from
one point in the Universe to another.

Credits:

ESA

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Astronomers thought the Universe
was a mostly peaceful place....

However, compared with the millions of years it takes for galaxies to
merge, the final cataclysm at the cores would be relatively brief. So the
odds of seeing such an event are small.
Until as recently as 50 years ago, astronomers thought the Universe was a
mostly peaceful place. But we now know that this is far from reality. Space
is often shaken by violent events: cataclysmic explosions of supernovae,
collisions of whole galaxies and the tremendous outpouring of energy due to
the large amount of matter crashing into black holes.
The discovery of quasars gave us the first clear glimpse of this turmoil.
To groundbased telescopes, quasars look like normal stars. And that is
exactly what astronomers first thought they were, naming them "Quasi
stellar" objects. However, quasars are in fact much brighter and further
away than stars. They can shine more brightly than 1,000 normal galaxies
and are powered by supermassive black holes.
Hubble has now observed several quasars and found that each resides at the
centre of a galaxy. Today most scientists believe that all quasars are
powered by a central, supermassive black hole that may weigh as much as a
few billion Solar masses.
Stars that orbit too close are pulled apart, draining into the quasar like
water into an enormous cosmic plug-hole. The spiralling gas forms a thick
disk, heated to a high temperature by its free-fall motion towards the
black hole. The gas blasts its energy into space above and below the disk
in colossal jets.
Quasars are found in a wide range of galaxies, many of which are violently
colliding. There appear to be a variety of mechanisms for igniting quasars.
Collisions between pairs of galaxies could trigger the birth of quasars,
but Hubble has shown that even apparently normal, undisturbed galaxies
harbour quasars.

Box:

Quasars are driven by supermassive black holes

The spinning supermassive black holes that drive quasars are generally
wrapped in a thick, opaque belt of dusty gas that slowly feeds material
into the core. This means that, from some directions, the quasar is hidden
from our direct view and we see the results of its prodigious energy
production only indirectly. It took several decades for astronomers to
realise that these heavily obscured galactic nuclei and the brilliant
quasars were actually similar objects viewed from their 'equators' or from
their 'poles'.

Credits:

The Hubble Heritage Team (STScI/AURA) and NASA/ESA

P77

Caption:

A cosmic searchlight

One of nature's most amazing phenomena, a black-hole-powered jet of
electrons and other sub-atomic particles traveling at nearly the speed of
light streams out from the centre of the galaxy M87 like a cosmic
searchlight. In this Hubble telescope image, the blue jet contrasts with
the yellow glow from the combined light of billions of unseen stars and the
yellow, point-like clusters of stars that make up this galaxy. Lying at the
centre of M87, the monstrous black hole has swallowed up matter equal to 2
billion times our Sun's mass. M87 is 50 million light-years from Earth.

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The energy they release is equal to the
amount of energy radiated by our whole
Milky Way over a couple of centuries.

But quasars are not the only high energy objects astronomers have found. A
serendipitous discovery is something you find while you're looking for
something else. Such discoveries have often changed the course of
astronomy. Gamma Ray Bursts were discovered serendipitously in the late
1960s by US military satellites that were on the lookout for Soviet nuclear
tests. Instead of finding the most powerful detonations produced by humans,
some of the most powerful blasts in the Universe itself were spotted.
These astoundingly energetic blasts of gamma rays are detected at least
once per day from random directions in the sky. Although Gamma Ray Bursts
last only a few seconds, the energy they release is equal to the amount of
energy radiated by our whole Milky Way over a couple of centuries.
Gamma rays are not visible to the human eye, and special instrumentation is
needed to detect them. For 30 years, no one knew what caused these bursts.
It was like seeing the gamma-ray bullet fly by Earth without ever glimpsing
the weapon that fired it. Together with nearly all other telescopes in the
world Hubble looked for the 'smoking gun' for many years. It observed the
positions in the sky where gamma ray explosions had been seen, trying to
find any object at that location. But all efforts were in vain, until, in
1999, Hubble observations were fundamental in determining that these
monstrous outbursts take place in far distant galaxies. After Hubble's
observations of the atypical supernova SN1998bw and the Gamma Ray Burst GRB
980425, scientists began to see a physical association between these two
phenomena.
The cause could be the blast produced in the final cataclysmic collapse of
a massive star or the dramatic encounter of two very dense objects, such as
two black holes, or a black hole and a neutron star.
Black holes are certainly some of the most exotic objects in the Universe.
As well as affecting matter they can also show up in some other spectacular
ways because their enormous gravitational fields can also deflect light.
In fact, rays of light that pass close to a black hole will not follow
straight lines, but will be bent onto new paths, creating a natural
telescope that can peer further into space than ever thought possible.

Caption:

Gamma Ray Burst (artist's impression)

Discovered by military satellites and for many years a complete mystery,
Gamma Ray Bursts appear at random places in the sky. With the aid of Hubble
these enigmatic sources have now been identified as exploding sources in
galaxies throughout the Universe. This artist's impression illustrates the
devastating influence such an event has on its host galaxy.

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Credits:

ESA


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7 Gravitational
Illusions

Einstein realised that concentrations of mass could bend passing light
rays. He would have been delighted - and staggered - to see the stunningly
beautiful images taken by Hubble of clusters of galaxies: the largest
aggregations of mass in the Universe. These clusters act as 'gravitational
lenses' that magnify and distort the images of more distant galaxies into
arcs and multiple images that can be measured to map the distribution of
mass - both luminous and dark - in space. Sometimes, these gravitational
lenses act as telescopes that amplify the feeble radiation from objects
beyond the limit of normal detection, rendering visible the most distant
objects ever detected in the young Universe.

Caption:

Gravitational lensing in Abell 1689

Light does not always travel in straight lines. Einstein's Theory of
General Relativity predicts that sufficiently massive objects such as a
cluster of galaxies will deform the structure of space itself so that when
light passes one of these objects, its path is curved slightly. The effect
is called gravitational lensing. The galaxy cluster Abell 1689 is so heavy
that it bends the light from background galaxies into hundreds of
gravitational arcs.

Credits:

NASA, ESA and the ACS Science Team

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Gravity warps space and therefore
distorts rays of light

Just as a wanderer in the desert sees a mirage when light from remote
objects is bent by the warm air hovering just above the sand, we may also
see mirages in the Universe. Those that we see with a modern telescope such
as the Hubble Space Telescope do not arise from warm air, but instead from
remote clusters of galaxies - huge concentrations of matter.
Long ago some people thought the Earth was flat. This is in some way
understandable since in our daily life we can't see the curvature of our
planet. Space itself is actually curved, although we can't see this for
ourselves on a starry night. But the curvature of space does create
phenomena that we can observe.
One of Albert Einstein's predictions is that gravity warps space and
therefore distorts rays of light, in the same way that ripples on a pond
create a warped honeycomb pattern of light on the sandy bottom.
Light from distant galaxies is distorted and magnified by the gravitational
field of massive galaxy clusters on its path to Earth. The effect is like
looking through a giant magnifying glass and the result is called
gravitational lensing.
The weird patterns that rays of light create when they encounter a weighty
object depend on the nature of the 'lensing body'. Thus, the background
object can appear in several guises.
Though Einstein realized in 1915 that this effect would happen in space, he
thought it could never be observed from Earth. However, in 1919 his
calculations were indeed proved to be correct. During a solar eclipse
expedition to Principe Island near the west coast of Africa, led by the
renowned British astronomer Arthur Eddington, the positions of stars around
the obscured solar disk were observed. It was found that the stars had
moved a small but measurable distance outwards on the sky compared with
when the Sun was not in the vicinity.
Nowadays, faint gravitational images of objects in the distant Universe are
observed with the best telescopes on Earth and, of course, with the sharp-
sighted Hubble.
Hubble's sensitivity and high resolution allow it to observe numerous
faint and distant gravitational lenses that cannot be detected with ground-
based telescopes due to the blurring introduced by the Earth's atmosphere.
The gravitational lensing results in multiple images of the original
galaxy, many with a characteristically distorted, banana-like shape. Hubble
was the first telescope to resolve details within the multiple arcs,
revealing the form and internal structure of the lensed background objects
directly.

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Captions:

Gravitational lenses

Gravitational lenses produce different shaped images depending on the shape
of the lensing body. If the lens is spherical then the image appears as an
Einstein ring (in other words as a ring of light) (top); if the lens is
elongated then the image is an Einstein cross (it appears split into four
distinct images) (middle), and if the lens is a galaxy cluster then arcs
and arclets (banana-shaped images) of light are formed (bottom).

Credits:

ESA

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Captions:

The galaxy cluster Abell 2218

This image shows the full WFPC2 overview of the galaxy cluster Abell 2218.
It was taken by Hubble in 1999 immediately after Servicing Mission 3A.
Acting like a cosmic magnifying glass, the massive cluster produces a
myriad arclets: distorted images of much more distant galaxies.
Credits:
NASA, ESA, A. Fruchter and the ERO Team (STScI, ST-ECF)



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Credits:

NASA, ESA, A. Fruchter and the ERO Team (STScI, ST-ECF)

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In 2003, astronomers deduced that a mysterious arc of light on one of
Hubble's images was the biggest, brightest and hottest star-forming region
ever seen in space.
It takes fairly massive objects, for example, clusters of galaxies, to make
space curve so much that the effect is observable in deep images of the
distant Universe even with Hubble's astonishing resolution. Gravitational
lenses have mainly been observed around clusters of galaxies - collections
of hundreds or thousands of galaxies. They are thought to be the largest
gravitationally bound structures in the Universe.
Astronomers know that the matter we see in the Universe is just a tiny
percentage of the total mass that must be there. For matter exerts a
gravitational force, and the visible material is simply not enough to hold
galaxies and clusters of galaxies together.
Since the amount of warping of the 'banana'-shaped images depends on the
total mass of the lens, gravitational lensing can be used to 'weigh'
clusters and to understand the distribution of the hidden dark matter. On
clear images from Hubble one can usually associate the different arcs
coming from the same background galaxy by eye. This process allows
astronomers to study the details of galaxies in the young Universe and too
far away to be seen with the present technology and telescopes.
A gravitational lens can even act as a kind of 'natural telescope'. In
2004, Hubble was able to detect the most distant galaxy in the known
Universe, using the magnification from just such a 'gravitational lens' in
space.

Caption:

The first heavy elements

Artist's impression of a quasar located in a primeval galaxy (or
protogalaxy) a few hundred million years after the Big Bang. Astronomers
used Hubble to discover substantial amounts of iron in three very distant
quasars. This was the first time that anyone had found elements believed to
have been created exclusively by the first generation of stars to
illuminate the young Universe.

Credits:
ESA

P87

Caption:

The most distant galaxies

Close-up of the large galaxy cluster Abell 2218 (also seen on the preceding
pages) showing how this cluster acts as one of nature's most powerful
'gravitational telescopes', amplifying and stretching the images of all
galaxies lying behind the cluster core (seen as red, orange and blue arcs).
Such natural gravitational 'telescopes' allow astronomers to see extremely
distant and faint objects that would otherwise not be seen. A new galaxy
(split into two images marked with an ellipse and a circle) was detected in
this image. The extremely faint galaxy is so far away that its visible
light has been stretched into infrared wavelengths, making the observations
particularly difficult. The galaxy has set a new record in being the most
distant known galaxy in the Universe so far. Located an estimated 13
billion light-years away (redshift around 7), the object is being viewed at
a time only 750 million years after the Big Bang, when the Universe was
barely 5 percent of its current age. In this image the distant galaxy
appears as multiple 'images', an arc (left) and a dot (right), as its light
is forced along different paths through the cluster's complex clumps of
mass (the yellow galaxies) where the magnification is quite large. The
colours of the differently lensed galaxies in the image depend on their
distances and galaxy types. The orange arc is, for instance, an elliptical
galaxy at moderate redshift (around 0.7) and the blue arcs are star-forming
galaxies at intermediate redshift (between 1 and 2.5).

Credits:
European Space Agency, NASA, J.-P. Kneib (Observatoire Midi-PyrИnИes) and
R. Ellis (Caltech)


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8 Birth and Death of the Universe

Telescopes are time machines. Light takes time to cross the vastness of
space, so looking further away means looking back in time. This produces
the mind-wrenching idea that Hubble can spend a few hours looking at
galaxies as they were in the early history of the Universe. It can then be
re-pointed to look during the next few hours at old stars in a nearby
galaxy that were formed billions of years ago - at the very same time as
the young galaxies it had just been observing were emitting their light.
Hubble is being used to sample different historical epochs. By observing
nearby Cepheid variable stars and distant supernovae it is mapping the
large-scale properties and long term history of the Universe to determine
its ultimate fate.

Craption:

Stars in NGC 300

Myriads of stars embedded in the heart of the nearby galaxy NGC 300 can be
singled out like grains of sand on a beach in this Hubble image. The
telescope's exquisite resolution enables it to see the stars as individual
points of light, despite the fact that the galaxy is millions of light-
years away. NGC 300 is a spiral galaxy similar to our own Milky Way galaxy.
It is a member of a nearby group of galaxies known as the Sculptor group,
named after the southern constellation where the group can be found. The
distance to NGC 300 is 6.5 million light-years, making it one of the Milky
Way's closer neighbours. At this distance, only the brightest stars can be
picked out from ground-based images.


Credits:

NASA, ESA, and The Hubble Heritage Team (AURA/STScI)

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Who hasn't thought about what it
would be like to travel in time?

Light may travel through a vacuum at the highest speed anything can ever
reach, but it is still a finite speed. This means that it takes a while for
rays of light to travel between two points in space.
The speed of light through space is about 300,000 kilometres per second.
300,000 kilometres is nearly the distance from the Earth to the Moon. So it
takes light just over a second to travel from the Moon to the Earth. When
we look at the Moon we see it as it was just over a second ago. Who hasn't
thought about what it would be like to travel in time?
The finite speed of light enables us to do the next best thing by allowing
us to look back in time. When looking out into space, we just need to wait
for the light from distant places to reach us, and it shows us how things
were when the light began its journey.
Powerful instruments, like Hubble, have made it possible to look farther
out and farther back than ever before. What cosmologists are seeing is
simply astounding.
In the 1920s, astronomer Edwin Hubble discovered that most galaxies appear
to be moving away from us at a rate proportional to their distance. The
farther away a galaxy is, the faster it appears to be moving away from us.
This is due to the expansion of the Universe.
That expansion began in a titanic explosion, called the Big Bang, many
billions of years ago. The rate of expansion holds the key to estimating
the age and size of the Universe. This rate is called the Hubble constant.
The age and size of the Universe can be estimated by 'running the expansion
backwards' - until everything is compressed into that infinitely small
point of energy from which the Universe was generated.
The top ranked scientific justification for building Hubble was to
determine the size and age of the Universe. The quest to determine the
Hubble constant precisely was headed by the Key Project team, a group of
astronomers who used Hubble to look for remote, accurate 'milepost
markers', a special class of stars called Cepheid variables.
Cepheids have very stable and predictable brightness variations. The period
of these variations depends strictly on the physical properties of the
star, which can be used to determine their distance very effectively. For
this reason these stars are known as 'standard candles'. The Cepheids have
been used as reliable stepping-stones to make distance measurements to
supernovae, which are much brighter than Cepheids and so can be seen at far
greater distances.
Due to its high resolution, Hubble has measured the light from supernova
explosions more accurately than any other instrument. From the ground an
image of a supernova usually blends in with the image of its host galaxy.
Hubble can clearly distinguish the light from the two sources.

Caption:

The Big Bang - The origin of our Universe (artist's impression)

This event created the time and the space within which the Universe has
evolved over the remaining 14 billion years to form the Universe we see
around us today.

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Credits:
ESA

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Credits:

Jeffrey Newman (Univ. of California at Berkeley) and NASA/ESA

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Caption:

Cepheids as standard candles

Several groups of astronomers have used Hubble to observe a special type of
variable star called a Cepheid. The brightness of a Cepheid varies in a
very stable and predictable manner that depends on the physical properties
of the star such as mass and absolute brightness. This means that
astronomers, just by measuring the variation in the light from these stars,
can effectively determine their distance. For this reason, cosmologists
call Cepheids 'standard candles'. The magnificent spiral galaxy NGC 4603,
seen here, is one of the most distant galaxies in which Cepheids have been
observed with Hubble.

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Cosmologists have called this
nightmare scenario, the Big Rip

Cepheids and supernovae have given a measure for the scale of the Universe.
Today we know the age of the Universe to a much higher precision than ever
before: around 14 billion years.
With Hubble the rate of expansion of the Universe, known to astronomers as
the "Hubble Constant", was determined. After eight years of Cepheid
observations, this work was concluded by finding that the apparent speed of
recession in all directions increases by 70 km/second for every 3.26
million light-years you look further out into space.
For many years astronomers have discussed whether the expansion of the
Universe would stop in some distant future, making the Universe collapse in
a fiery "Big Crunch", or whether it would continue to expand ever more
slowly. Combined observations of distant supernovae with Hubble and most of
the world's top-class telescopes were used to measure distances to remote
supernovae. And it looks like the expansion of our Universe is nowhere near
slowing down. Instead, it seems to be speeding up.
When Hubble was used to measure how the expansion of the Universe has
changed with time, it turned out, quite surprisingly, that during the first
half of cosmic history, the expansion rate was actually slowing down. Then,
a mysterious force, a sort of 'anti-gravity' made the Universe 'hit the
accelerator' starting the acceleration we see today.
This suggests an extraordinary fate for the Universe because it implies
that the anti-gravity force is getting stronger all the time. If this
continues, it will eventually overwhelm all gravity and catapult the
Universe into a super fast acceleration that will shred everything into its
constituent atoms. Cosmologists have called this nightmare scenario, the
Big Rip.

Caption:

Zooming in on a supernova explosion

The explosion of a massive star blazes with the light of 200 million Suns.
The supernova - seen in the upper right corner - is so bright in this image
that it easily could be mistaken for a foreground star in our Milky Way
Galaxy. And yet, this supernova, called SN 2004dj, resides far beyond our
galaxy. Its home is in the outskirts of NGC 2403, a galaxy located 11
million light-years from Earth. Although the supernova is far from Earth,
it is the closest stellar explosion discovered in more than a decade.
Hubble's sharp vision means that it can see supernovae that are difficult
to study with other telescopes. A supernova image from the ground usually
blends with the image of its host galaxy. Hubble can distinguish the light
from the two sources and thus measure the supernova itself directly.

Credits:

NASA, ESA, A.V. Filippenko (University of California, Berkeley), P. Challis
(Harvard-Smithsonian Center for Astrophysics), et al.

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9 NASA, ESA, A.V. Filippenko (University of California, Berkeley), P.
Challis (Harvard-Smithsonian Center for Astrophysics), et al.

By taking the first very long, high-resolution images of the sky, Hubble
created a new branch of astronomy: the direct study of galaxies in the
young Universe. These long-exposure 'deep field' observations are being
examined by many astronomers throughout the world and are stimulating
follow-up observations with the largest ground-based telescopes to create a
comprehensive picture of the assembly and subsequent evolution of galaxies
throughout the history of the Universe.

Caption:

The first deep fields

Hubble Deep Field North and South gave astronomers a peephole into the
ancient Universe for the first time, and have caused a revolution in modern
astronomy.

Some of the objects viewed on the images were so dim that seeing them would
be as difficult as discerning a flashlight on the Moon from Earth.

Credits:

Robert Williams and the Hubble Deep Field Team (STScI) and NASA/ESA

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Pointing the world's most sophisticated
telescope at the same piece of sky for ten
days in a row may sound a bit strange

We are collecting exclusive news from deep space. Just as geologists dig
deeper underground to find ever more ancient fossils, bearing witness to
ever more remote epochs, so astronomers 'excavate' deeper and deeper
towards the beginning of time, by looking for light coming from fainter,
and thus more distant, objects.
Hubble started a new era we could call 'astroarcheology' and it began over
Christmas, 1995. Pointing the world's most sophisticated telescope at the
same piece of sky for ten days in a row may sound a bit strange. And this
was what many astronomers thought when they tried it for the first time at
the end of 1995. Deep field observations are very long exposures pointing
at a particular region of the sky. They aim to reveal faint objects by
collecting as much light as possible over a long period of time. The
'deeper' an observation goes, the fainter the objects that become visible
are. Objects in the sky can either look faint because their intrinsic
brightness is low, or because their distance is great.
When this experiment was first proposed, nobody really knew if this would
lead to any interesting scientific results. But when they examined the
first image astronomers were astonished! More than 3000 galaxies could be
counted in this small field.
The thousands of galaxies observed in the first Deep Field were at various
stages of evolution and were strung out along a corridor billions of light-
years long. This allowed the study of the evolution of these objects
through time, glimpsing different galaxies at different stages of their
lives.
The observed region of sky in Ursa Major, the Plough, was carefully
selected to be as empty as possible so that Hubble would look far beyond
the stars of our own Milky Way and out past nearby galaxies.

Box:

Deep Fields

Deep fields result from lengthy observations of a particular region of the
sky. They are intended to reveal faint objects by collecting their light
for an appropriately long time. The 'deeper' the observation (i.e. the
longer the exposure time), the fainter the objects that become visible are.
Astronomical objects can either look faint because their natural brightness
is feeble, or because they are very distant.

In making a 'deep field' observation, the telescope is not simply pointed
in exactly the same direction with the shutter open for days or weeks. It
will actually take many separate observations with the telescope moved a
very small amount between each. This is called 'dithering' and, when the
dithered exposures are combined, the resulting image is free from many of
the small defects that would appear in a single pointing. By taking many
exposures, it is also possible to identify and remove nearly all of the
'false stars' created when the many energetic particles found in space
collide with the detector and leave trails of exposed pixels.

Caption:

Hubble Ultra Deep Field close-up

These close-up snapshots of galaxies reveal the drama of galactic life and
were plucked from a harvest of nearly 10,000 galaxies in the Ultra Deep
Field. Almost every panel is littered with oddball-shaped galaxies that are
the results of close encounters with other galactic neighbours.

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After the first deep field, another long exposure was taken in the southern
sky. Together the Hubble Deep Field North and South gave astronomers
peepholes into the early Universe for the first time.
The Hubble Deep Fields have caused a real revolution in modern astronomy.
After the first Deep Field was observed, almost all of the most powerful
ground- and space-based telescopes were pointed at this same area for long
periods. Some of the most interesting results in astronomy emerged from
this fruitful synergy between instruments of different sizes, in different
environments and with sensitivity to different wavelengths.
They gave us the first clear picture of the rate of star formation
throughout the Universe. It showed that star formation peaked during the
first half of the Universe's life. At that time, over ten times more stars
were forming than today. This was also the epoch when quasars were hundreds
of times more common than they are now.
Once they had begun to discover the most distant Universe ever seen, Hubble
astronomers tried to push their observations even farther back in time. In
2003 and 2004, Hubble performed its deepest exposure ever: the Hubble Ultra
Deep Field. It is a 28 day-long exposure, going much deeper than the
earlier Hubble Deep Fields North and South


Credits:

NASA, ESA, and S. Beckwith (STScI) and the HUDF Team

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Credits:

NASA, ESA, and S. Beckwith (STScI) and the HUDF Team

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Caption:

The Hubble Ultra Deep Field from 2004 represents the deepest portrait of
the visible Universe yet achieved by mankind. It reveals the first galaxies
to emerge from the 'dark ages', the time shortly after the big bang when
the first stars reheated the cold, dim Universe. Some may be the most
remote ever seen, existing when the Universe was just 400 million years
old.

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Perhaps Hubble's greatest legacy has
been to open our eyes to the incredible
beauty of nature - not only 'out there' in
the depths of cosmos, but also
everywhere around us in our daily lives...

The Hubble Ultra Deep Field reveals the first galaxies to emerge from the
so-called "dark ages" - the time shortly after the Big Bang when the first
stars reheated the cold, dark Universe. Just after the Big Bang, in the
newborn fast-expanding Univers - before the era of the stars and galaxies -
the distribution of matter was fairly smooth. As time went on, the king of
all forces - gravity - started acting. Slowly, but steadily.
Under the influence of gravity from the mysterious dark matter, small
clumps of normal matter started to coalesce in regions where the density
was slightly higher than average. With no stars to light up space, the
Universe was in its dark age. Where the density of the clumps became
higher, even more matter was attracted, and a competition between the
expansion of space and gravity took place. Where gravity won, regions
stopped expanding, and started to collapse in on themselves. The first
stars and galaxies were born. Where the matter density was highest - at the
intersections between the large web-like structures of matter - the largest
structures we know were formed: clusters of galaxies.
The Deep Field images are studded with a wide range of galaxies of various
sizes, shapes, and colours. Astronomers will spend years studying the
myriad shapes and colours of the galaxies in this image to understand how
they formed and have evolved since the Big Bang.
In vibrant contrast to the image's rich harvest of classic spiral and
elliptical galaxies, there is also a zoo of oddball galaxies littering the
field. Some look like toothpicks; others like links on a bracelet. A few
appear to be interacting with each other. Their strange shapes are a far
cry from the majestic spiral and elliptical galaxies we see around us
today. These oddball galaxies chronicle a period when the Universe was more
chaotic, when order and structure were just beginning to emerge and
galaxies were being assembled from smaller pieces.
One of the great things about Hubble is that there are many instruments
onboard that can make different observations at the same time. The Hubble
Ultra Deep Field is actually two separate images taken by two instruments:
Hubble's ACS camera and the NICMOS instrument. NICMOS can see even farther
than the ACS. It detects infrared light, and so it is able to reveal the
farthest galaxies ever seen because the expanding Universe has stretched
and weakened the light from these objects so much that, they are now only
visible at infrared wavelengths.

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The Hubble Ultra Deep Field is likely to remain the deepest image of the
Universe for the next decade or so, until an ESA Ariane rocket launches the
James Webb Space Telescope in 2011.
Up until today, during the first 15 years of its life, Hubble has orbited
the Earth 80,000 times. This is nearly 4 billion kilometres or more than 25
times the distance from the Earth to the Sun. Hubble has taken more than
700,000 exposures of the Universe and created a visual heritage that has
shaped the way humanity looks at the Universe today.
But perhaps Hubble's greatest legacy has been to open our eyes to the
incredible beauty of nature - not only 'out there' in the depths of cosmos,
but also everywhere around us in our daily lives.
And it's nowhere finished yet.

Caption:

The evolution of large-scale structure

These four frames show a sequence of computer simulations of the evolution
of the large-scale distribution of matter, both luminous and dark, as
gravity inexorably shapes the Universe.

Credits:

John Dubinsky

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10 HUBBLE GALLERY

Since the launch of Hubble 15 years ago, the public has been treated to
striking images of jewel-like star clusters, colourful star-forming regions
and colliding galaxies. However, the data from Hubble itself are greyscale
and have to be manually processed and combined, filter by filter, to create
the colourful and detailed images. This is done using software such as
Photoshop and the ESA/ESO/NASA Photoshop FITS Liberator. On the following
pages we present some more of these iconic images.

Caption:

The Ring Nebula

The sharpest view yet of the most famous of all planetary nebulae: the Ring
Nebula (M57). In this image the telescope has looked down a barrel of gas
cast off by a dying star thousands of years ago. This photo reveals
elongated dark clumps of material embedded in the gas at the edge of the
nebula; the dying central star is floating in a blue haze of hot gas. The
nebula is about a light-year in diameter and is located some 2,000 light-
years from Earth in the direction of the constellation Lyra.

Credits:

Hubble Heritage Team (AURA/STScI/NASA) and ESA

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Caption:

Thackeray's Globules in IC 2944

Strangely glowing dark clouds float serenely in this remarkable and
beautiful image taken with the Hubble's WFPC2. These dense, opaque dust
clouds - known as 'globules' - are silhouetted against nearby bright stars
in the busy star-forming region, IC 2944. Astronomer A.D. Thackeray first
spied the globules in IC 2944 in 1950. Globules like these have been known
since Dutch-American astronomer Bart Bok first drew attention to such
objects in 1947.

Credits:

NASA/ESA and The Hubble Heritage Team (STScI/AURA)

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Caption:

Star-forming region in Messier 33

NGC 604 provides Hubble astronomers with a nearby example of a giant star-
birth region. Such regions are small-scale versions of more distant
"starburst" galaxies, which undergo an extremely high rate of star
formation. Starbursts are believed to have been common in the early
universe, when the star-formation rate was much higher. Supernovae
exploding in these galaxies created the first chemical elements heavier
than hydrogen and helium.

Credits:

NASA/ESA and The Hubble Heritage Team (AURA/STScI)

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Caption:

Demise in ice and fire

The Bug Nebula, NGC 6302, is one of the brightest and most extreme
planetary nebulae known. At its centre lies a super-hot, dying star
smothered in a blanket of hailstones. This Hubble image reveals fresh
detail in the wings of this cosmic butterfly.

Credits:

ESA/NASA and Albert Zijlstra

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Caption:

Ghostly Reflections in the Pleiades

Hubble has caught the eerie, wispy tendrils of a dark interstellar cloud
being destroyed by the passage of one of the brightest stars in the
Pleiades star cluster. Viewed indirectly, like seeing a flashlight beam
shining off the wall of a cave, the star is reflecting light from the
surface of pitch black clouds of cold gas laced with dust. These are called
reflection nebulae.

Credits:

NASA/ESA and The Hubble Heritage Team (STScI/AURA), George Herbig and
Theodore Simon

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Caption:

Grazing Encounter Between two Spiral Galaxies

In the direction of the constellation Canis Major, two spiral galaxies pass
by each other like majestic ships in the night. The near-collision has been
caught in images taken by Hubble's WFPC2.

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Credits:

NASA/ESA and The Hubble Heritage Team (STScI)


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Caption:

The Red Spider Nebula in Sagittarius

Hubble observations have revealed huge waves sculpted in the Red Spider
Nebula. This warm and windy planetary nebula harbours one of the hottest
stars in the Universe and its powerful stellar winds generate waves 100
billion kilometres high.

Credits:

ESA & Garrelt Mellema (Leiden University, the Netherlands)

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Caption:

Saturn in Natural Colours

Hubble has provided images of Saturn in many colours, from black-and-white,
to orange, to blue, green, and red. But in this picture, image processing
specialists have worked to provide a crisp, extremely accurate view of
Saturn, which highlights the planet's pastel colors. Bands of subtle colour
- yellows, browns, greys - distinguish differences in the clouds over
Saturn, the second largest planet in the solar system.

Credits:

Hubble Heritage Team (AURA/STScI/NASA) and ESA

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Caption:

The Boomerang Nebula

The Boomerang Nebula is a young planetary nebula and the coldest object
found in the Universe so far. This is yet another example of how Hubble's
sharp eye reveals surprising details in celestial objects. The Nebula is
one of the Universe's peculiar places. In 1995, using the 15-metre Swedish
ESO Submillimetre Telescope in Chile, astronomers revealed that it is the
coldest place in the Universe found so far. With a temperature of -272њC,
it is only 1 degree warmer than absolute zero (the lowest limit for all
temperatures). Even the -270њC background glow from the Big Bang is warmer
than this nebula. It is the only object found so far that has a temperature
lower than the background radiation. This Hubble image was taken in 1998.
It shows faint arcs and ghostly filaments embedded within the diffuse gas
of the nebula's smooth 'bow tie' lobes. The diffuse bow-tie shape of this
nebula makes it quite different from other observed planetary nebulae,
which normally have lobes that look more like 'bubbles' blown in the gas.
However, the Boomerang Nebula is so young that it may not have had time to
develop these structures. Why planetary nebulae have so many different
shapes is still a mystery.

Credits:

European Space Agency and NASA

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Caption:

A swarm of ancient stars

This stellar swarm is M80 (NGC 6093), one of the densest of the about 150
known globular star clusters in the Milky Way galaxy. Located about 28,000
light-years from Earth, M80 contains hundreds of thousands of stars, all
held together by their mutual gravitational attraction. Globular clusters
are particularly useful for studying stellar evolution, since all of the
stars in the cluster have the same age but cover a range of stellar masses.
Every star visible in this image is either more highly evolved than, or in
a few rare cases more massive than, our own Sun. Especially obvious are the
bright red giants, which are stars similar to the Sun in mass that are
nearing the ends of their lives.

Credits:

The Hubble Heritage Team (AURA/STScI/NASA) and ESA

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Caption:

The Heart of the Trifid Nebula

Three huge intersecting dark lanes of interstellar dust make the Trifid
Nebula one of the most recognizable and striking star birth regions in the
night sky. The dust, silhouetted against glowing gas and illuminated by
starlight, cradles the bright stars at the heart of the Trifid Nebula. This
nebula, also known as Messier 20 and NGC 6514, lies within our own Milky
Way Galaxy about 9,000 light-years from Earth, in the constellation
Sagittarius.

Credits:

NASA, ESA, and The Hubble Heritage Team (AURA/STScI)

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Caption:

Star formation in the Large Magellanic Cloud

Hubble captures the iridescent tapestry of star birth in a neighbouring
galaxy in this panoramic view of glowing gas, dark dust clouds, and young,
hot stars. The star-forming region, catalogued as N11B lies in the Large
Magellanic Cloud (LMC), is located only 160,000 light-years from Earth.
With its high resolution, the telescope is able to view details of star
formation in the LMC as easily as ground-based telescopes are able to
observe stellar formation within our own Milky Way galaxy.

Credits:

NASA/ESA and the Hubble Heritage Team (AURA/STScI)/HEIC

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Caption:

The Helix Nebula

The image of the Helix Nebula shows a fine web of filamentary "bicycle-
spoke" features embedded in the colourful red and blue gas ring, which is
one of the nearest planetary nebulae to Earth. The tentacles formed when a
hot "stellar wind" of gas plowed into colder shells of dust and gas ejected
previously by the doomed star.

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Credits:

NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A.
Rector (NRAO).

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Caption:

Multiple generations of stars in the Tarantula Nebula

Hodge 301, seen in the lower right hand corner of this image, lives inside
the Tarantula Nebula in our galactic neighbour, the Large Magellanic Cloud.
Many of the stars in Hodge 301 are so old that they have exploded as
supernovae. These exploded stars are blasting material out into the
surrounding region. This high speed ejecta are plowing into the surrounding
Tarantula Nebula, shocking and compressing the gas into a multitude of
sheets and filaments, seen in the upper left portion of the picture.

Credits:

Hubble Heritage Team (AURA/STScI/NASA) and ESA