A SUPERNOVA seen in 2005 may be a new type of cosmic explosion. What’s more, similar explosions may have scattered antimatter throughout our galaxy.
“SN 2005E” exploded in a galaxy 100 million light years away. A team led by Hagai Perets at the Weizmann Institute of Science in Rehovot, Israel, has concluded that it does not look like either of the well-known kinds of supernova
The most frequently observed form is a core-collapse supernova, which happens after a massive young star has formed a large core of iron that collapses under its own gravity, releasing radiation that blows the outer layers of the star apart. They almost always occur in regions where massive new stars are forming. By contrast, SN 2005E was in the dark outskirts of its galaxy, where few new stars are forming. Core-collapse supernovae also spit out much more debris than SN 2005E did.
To date, the only other known supernova mechanism is a type la supernova, in which a small, dense white dwarf star steals hydrogen gas from a larger companion star. The gas builds up, gradually compressing the white dwarf until it reaches a critical point at which carbon starts to burn in an explosive thermonuclear reaction. SN 2005E doesn’t look like one of these explosions either - it faded much faster than a type la usually does, and the spectrum of its light reveals unusually high quantities of calcium in the explosion’s ashes.
So what happened? Perets says the calcium and other chemicals could have been produced by a helium-fuelled explosion. One possibility is that SN 2005E started out as a white dwarf stealing helium gas from a neighbouring helium-rich star, and that the gas accumulated into a thick layer before exploding.
Astronomer Craig Wheeler at the University of Texas at Austin says Peret’s hypothesis is plausible, but is not convinced that it represents a completely new type of stellar explosion.
If correct, however, the discovery could explain two astronomical anomalies. In the central bulge of our galaxy, astronomers see evidence of a surprisingly large quantity of psitrons - the antimatter counterparts of electrons. Helium-powered supernovae might supply most of this antimatter, as they should produce large quantities of the radioactive isotope titanium-44, which emits positrons.
Furthermore, titanium-44 decays into calcium-44, an isotope that accounts for about 2 per cent of the calcium in our solar system - the origin of which has been hard to account for. Perhaps an explosion akin to SN 2005E supplied our solar system with its calcium-44.
