By following the aftermath of a dramatic supernova explosion for two and a half years, from just weeks after it began, astronomers may have finally solved a mystery that has left scientists scratching their heads for years- where cosmic dust came from. They found that the supernova produced large dust grains that could resist destruction by shockwaves from the explosion. Furthermore, they found that the rate of dust production gradually increased over time, which could help explain the vast amount of dust found throughout the universe. The study has been published in Nature.
Stardust, or cosmic dust, is all around us; it’s the stuff that stars, planets and even people are made of. It’s composed of various elements such as carbon, oxygen and iron. While stars such as our Sun spit out dust as they get older, in the young cosmos these stars had not been around long enough to account for the huge amount of dust observed in early galaxies.
Another popular theory proposes that supernovas could be to blame, but previous observations of such events near our own galaxy indicated that they didn’t produce enough dust either. However, co-author of the latest study Christa Gall points out that they did not follow the explosions for long enough. This time, she and colleagues observed a supernova, SN 2010jl, for over two years.
Using the Very Large Telescope’s spectrograph, the researchers looked at both the visible light absorbed by dust particles and the infrared emitted by them. This allowed the team to measure dust composition and size.
They found that between 40-240 days after the explosion, the dust present must have originated before the event took place rather than coming from the supernova itself. This is because at this stage, it would be far too hot for debris to coalesce into particles.
How did the material withstand destruction by this dramatic event? The researchers suggest that the shockwave released by the supernova actually compressed the material into a cool shell, providing ideal conditions for the dust to come together. Furthermore, the particles were found to be very big, around 4 times the size of those typically found in the Milky Way, which would also help them resist obliteration.
Shortly after the event, the team found there wasn’t much dust around the explosion; probably around 1/10000 the mass of the Sun. However, after day 500 dust production significantly hastened and by day 868 the amount present had increased 10 fold. This is because the material ejected by the supernova had cooled enough to merge into dust particles.
When the team stopped observing, the amount of dust present was the equivalent of 0.04 solar masses. If dust production was occurring at a similar rate early in the universe, the researchers predict that multiple explosions could account for the vast amount of dust present in the young universe.