Astronomers Observe Star Dust Formation in Real Time
“It really is the most poetic thing I know about physics: You are all stardust.” -Lawrence Krauss
When stars explode, they scatter the elements they have been forging over billions of years out across the Universe. Those elements are then used to create things like new stars, planetary systems, elephants, and us. Shortly after the explosion, a dusty haze forms around the supernova. It has not been entirely clear how this dust forms and how it is able to persist in such a turbulent environment.
An international team led by Christa Gall from Aarhus University in Denmark used the ESO’s Very Large Telescope (VLT) and were able to witness the dust accumulating around a supernova, finally shedding light on this mystery. The results have been published in Nature.
Supernova SN2010jl, located about 160 million years away in the galaxy UGC 5189A, was an incredibly luminous explosion that was imaged by the VLT in visible and near-IR wavelengths. Observations were made nine times over a few months after the supernova was detected, and a final observation was made two and a half years later.
“By combining the data from the nine early sets of observations we were able to make the first direct measurements of how the dust around a supernova absorbs the different colours of light,” Gall said in a press release. “This allowed us to find out more about the dust than had been possible before.”
While the stardust first appears shortly after the explosion, it continues to form for quite a while. Between 500-868 days after the onset of dust formation, it entered a second phase where dust begins to form ten times more rapidly. The dust cloud is expected to continue to grow for the next few decades, until is has about half the mass of our Sun.
This study marks the first time that the onset of dust around a supernova was observed and was tracked over a long period of time. The team was also able to determine how the grains of dust were able to survive such a harsh environment: their surprisingly large size. The grains were measured 1-4 micrometers, which doesn’t seem all that huge, but is about 4 times larger than dust grains in the Milky Way. This gives astronomers answers they have been seeking for nearly 30 years.
“Our detection of large grains soon after the supernova explosion means that there must be a fast and efficient way to create them,” explained co-author Jens Hjorth. “We really don’t know exactly how this happens.”
The researchers believe that the dust may form from material had been ejected by the star before it exploded. When that material met the gas from the explosion’s shockwave, which is dense and cool, it could very well have created the conditions needed for the dust to form.
“Previously astronomers have seen plenty of dust in supernova remnants left over after the explosions. But they also only found evidence for small amounts of dust actually being created in the supernova explosions. These remarkable new observations explain how this apparent contradiction can be resolved,” Gall concluded.