Surprisingly low temperatures detected in the remnant of Supernova 1987A may explain the mystery of why space is so abundant with dust grains and molecules.
In 1987, an explosion of a massive star was detected in our neighboring galaxy, the Large Magellanic Cloud, just 170,000 light-years away. This supernova, dubbed 1987A, released approximately a thousand million times more energy than that emitted by the Sun in one year. Twenty-five years later, an international team of astronomers has used the Herschel Space Observatory and Atacama Large Millimeter/Submillimeter Array (ALMA) to study the supernova remnant. They found a vast reservoir of unexpectedly cold molecules and dust.
"The powerful explosion we saw in 1987 scattered elements made by the star into space in the form of a very hot plasma,” said Mikako Matsuura from University College London. “The gas has now cooled down to temperatures between –250° to –170° Celsius [–420° to –275° Fahrenheit]. That's surprisingly cold, comparable to the icy surface of Pluto at the edge of our solar system. The gas has formed molecules and some have even condensed into solid grains of dust. The supernova has now become a super freezer!"
The Herschel observations show that the supernova produced dust and solid material equal to about 250,000 times the mass of Earth, or three-quarters of the mass of the Sun. To date, scientists have believed that supernova remnants contain only very energetic atomic gas, detectable at optical X-ray wavelengths; the new observations show that this is not the case. The discovery of such a large mass of dust should help us understand how supernovae slowly spread and fill galaxies with gas, dust, and small rocky particles, some of which may eventually end up in the next generation of stars and planets.
"We were surprised by the amount of dust and molecular gas in the reservoir created by the Supernova 1987A,” said Matsuura. “The ALMA and Herschel observations show that the reservoir contains carbon monoxide molecules equaling one-tenth the mass of the Sun. Herschel shows that the dust mass was even larger — about half the solar mass!"
"We don't get many opportunities to study supernovae. These events are very rare and the majority was found in very distant galaxies,” said Matsuura. “Even with relatively close ones, like 1987A, it's difficult. Although they are very bright at the time of the explosion, the light from the supernovae fades very quickly making it very difficult to observe them a few years after the explosion. Carl Sagan once said that: 'We are all made of star-stuff.' These results will help us understand how that material reached us!"