Dust from star explosions

Iron needles in Supernovae?

Dust plays an important role in the cosmos. The small particles, which mainly consist of carbon and silicate help to form stars and are the basis for the development of planets like the Earth or the core of Mars. The question is: Where does that dust come from? An international team of astronomers succeeded in finding dust in the perimeter of Cassiopeia A, the remains of a supernova. The conclusion is that the explosion of stars produce a big chunk of the dust in the universe.
Cassiopeia A supernova remnant. The overlaid lines indicate the polarized signal from cold dust within the remnant with the strength marked by the length of each line. The temperature of this dust is around -250°C.

Cassiopeia A supernova remnant. The overlaid lines indicate the polarized signal from cold dust within the remnant with the strength marked by the length of each line. The temperature of this dust is around -250°C.



The interstellar dust found by Loretta Dunne from the University of Nottingham is unusual. The polarization signal from the supernova dust is the strongest ever measured anywhere in the Milky Way. “It is like nothing we’ve ever seen” said Loretta Dunne. “It could be that the extreme conditions inside the supernova remnant are responsible for the strong polarized signal, or it could be that the dust grains themselves are highly unusual” Professor Rob Ivison comments further.
Right after the Big Bang only hydrogen, helium and small amounts of lithium existed in the universe. All the heavier elements formed much later inside of stars. Dust could therefore develop in the hulls of old stars and be blown into space by some sort of "star wind". So far so good, but dust was already present in the very early times of the universe. Only stars with a lot of mass could have been the producers, since they already decease after a few million years as a supernova and blow the dust out.
Until now there was no convincing evidence for the theory that supernova explosions actually release enough dust. The observations of Dunne and her colleagues show that at least the explosion of the supernova Cassiopeia A generated large amounts.
The polarization of the radiation follows the magnetic field of Cassiopeia A, which is evidence for the theory that the dust actually belongs to the remnants of the supernova and is not just in the foreground or background. However the radiation and the polarization of the particles is stronger than expected from calculations. A possible explanation, which will be presented in the journal "Monthly Notices of the Royal Astronomical Society" is that the dust particles are actually little needles out of graphite or iron.

This could have major consequences for our understanding of the cosmic microwave background — one of the most important building blocks of the Big Bang model of our Universe and in the end help us to understand the history of the universe a little better.


Rainer Kayser is a journalist in Hamburg