The mystery of when and how the first solid particles in the Universe formed may have been solved, with the discovery of an exploded star that produced vast quantities of dust.
Cassiopeia A is the remnant of a supernova that exploded 300 years ago. Using the SCUBA instrument at the James Clerk Maxwell Telescope (JCMT) in Hawaii, Loretta Dunne, at Cardiff University, Wales, and colleagues, detected the faint glow of a cloud of frigid dust grains equivalent to at least double the mass of our Sun.
Infrared satellites have previously seen small quantities of dust in supernova remnants, at temperatures of -173 to -73°C. But, at -255°C, the dust that Dunne recorded is just 18 degrees above absolute zero.
It is the first time that the lower-temperature material in a supernova remnant has been probed and proved that the previous dust detections were only the tip of an astronomical iceberg. “We detected about a thousand times more dust than has previously been found,” Dunne told New Scientist.
Question of timing
Cosmic dust grains are the smallest solid objects in the Universe and represent the first step in a growth process that culminates in planets. Over the last five years, astronomers have built up evidence that the early Universe, at an age of around one billion years, already had vast clouds of cosmic dust.
But this caused a considerable problem because astronomers had believed that most of the dust in the Universe was formed in the rarefied outer atmospheres of red giant stars, where carbon and silicon molecules condense into soot-like particles.
The problem is that an ordinary star like the Sun takes nine billion years or so to become a red giant and thus begin producing dust. So astronomers had largely swept the problem under the carpet. However, the stars that produce supernovae are more massive and much shorter lived. From birth to death, they may only exist for 100 million years or so.
So, if other supernovae are as efficient at producing dust as Cassiopeia A, they could easily have produced the dust seen in the early Universe. This would have provided the raw material for planets billions of years earlier than previously thought.
“We now need to know if Cas A is an exception or a rule,” says Dunne. “So, we are investigating other young supernova remnants in the Milky Way to see if they also contain lots of dust – the early results are promising.”
Journal reference: Nature (vol 424, p 285)