Scientists led by Dr Christa Gall from Aarhus University, Denmark, have discovered that supernovas – the cosmic factories of gas and dust – produce grains of stardust in a two-stage process, starting soon after the explosion, but continuing for years afterwards.
This artist’s impression shows dust forming in the environment around a supernova explosion. Image credit: ESO / M. Kornmesser.
Researchers know that supernovas may be the primary source of dust, especially in the early Universe, but it is still unclear how and where dust grains condense and grow. It is also unclear how they avoid destruction in the harsh environment of a star-forming galaxy.
In attempt to shed light on these mysteries, Dr Gall and her colleagues have analyzed the light from SN 2010jl – a bright supernova in the galaxy UGC 5189A – as it slowly faded.
Using the X-shooter spectrograph at the ESO Very Large Telescope, they observed SN 2010jl nine times in the months following the explosion, and for a tenth time 2.5 years after the explosion.
The scientists found that dust formation starts soon after the explosion and continues over a long time period. They also found how big the dust grains are and what they are made of.
Dust grains larger than one thousandth of a millimeter in diameter formed rapidly in the dense material surrounding the star. Although still tiny by human standards, this is large for a grain of cosmic dust and the surprisingly large size makes them resistant to destructive processes.
“Our detection of large grains soon after the supernova explosion means that there must be a fast and efficient way to create them. We really don’t know exactly how this happens,” said Dr Jens Hjorth from the University of Copenhagen’s Niels Bohr Institute, who is a co-author of the paper published in the journal Nature.
This composite image of UGC 5189A shows X-ray data from Chandra in purple and optical data from Hubble Space Telescope in red, green and blue. SN 2010jl is the very bright X-ray source near the top of the galaxy (X-ray image: NASA / CXC / Royal Military College of Canada / P. Chandra et al; Optical image: NASA / STScI)
But the astronomers think they know where the new dust must have formed: in material that the star shed out into space even before it exploded.
As the supernova’s shockwave expanded outwards, it created a cool, dense shell of gas — just the sort of environment where dust grains could seed and grow.
Results from the observations indicate that in a second stage – after several hundred days – an accelerated dust formation process occurs involving ejected material from the supernova.
If the dust production in SN 2010jl continues to follow the observed trend, by 25 years after the supernova, the total mass of dust will be about half the mass of the Sun; similar to the dust mass observed in other supernovae such as SN 1987A.
_____
Christa Gall et al. Rapid formation of large dust grains in the luminous supernova 2010jl. Nature, published online July 09, 2014; doi: 10.1038/nature13558
