PG 1115+080: A Gravitational Cloverleaf
Explanation:
All four blue images in the
above photograph are the same object. The
gravitational lens effect of the red, foreground,
elliptical galaxy visible near image center creates a
cloverleaf image of the single distant
quasar.
Light from the
quasar is pulled around the massive galaxy in different paths, corresponding
to different images.
Light takes many billions of years to reach us from this quasar.
Since light takes a different amount of time to traverse each path,
each image shows the quasar as it appeared at a
slightly different time in the past, creating
time delays on the time scale of days.
Since these time delays are influenced by the
expansion rate of the universe,
analysis of this image helps reveal
Hubble's constant, the parameter that calibrates
universe expansion.
This recent picture by the new
Subaru Telescope
is perhaps the clearest image yet of this
famous optical mirage.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
NASA Web Site Statements, Warnings,
and Disclaimers
NASA Official: Jay Norris.
Specific
rights apply.
A service of:
LHEA at
NASA /
GSFC
& Michigan Tech. U.
