Dr Jérémy Chastenet | Solving the Mystery of Interstellar Dust Grains

In addition to flinging elements into space, supernova explosions also release a violent shockwave, which rebounds upon interacting with the surrounding gases. This so-called ‘reverse shock’ is believed to vaporise many of the dust grains formed after the explosion. As such, supernovae can lead to both the creation and destruction of interstellar dust grains.

Therefore, astronomers are trying to figure out whether these explosions are an overall ‘source’ or ‘sink’ of interstellar dust grains, and how the competing processes vary between different types of supernovae.

To answer these questions, scientists need to determine the sizes and compositions of dust grains when observing the remnants of supernovae, at different stages. This would allow them to determine how much dust was created after each explosion and how much was destroyed by the resulting reverse shock. Settling this debate could be an important step towards understanding the origins of star systems. After all, everything in our Solar System – including us – is made from stardust.

Towards this aim, a team of astronomers led by Dr Jérémy Chastenet at Ghent University studied dust grains in the Crab Nebula – the remnant of a supernova first documented by Chinese astronomers in 1054 – that has not yet experienced a ‘reverse shock’. Their research provides compelling evidence for dust grain formation that occurred after the explosion.

In the Crab Nebula, Dr Chastenet and his collaborators searched for characteristic frequencies of infrared light emitted by elongated dust grains. These dust grains have been aligned in the same direction by strong magnetic fields, due to a phenomenon called ‘polarisation’.

The signals they detected strongly hinted at the presence of large, aligned dust grains in the Crab Nebula, which are rich in both carbon and silicates. This result is somewhat at odds with models. As these grains are thought to be more resilient to shocks, this could mean that individual supernova events contribute a significant portion of the total dust budget of their host galaxies.

The team’s discovery offers important evidence for the origins of interstellar dust grains, along with new clues about how star systems form from the remnants of supernovae.