Astronomers learn that two white dwarfs do not make a supernova

Although every supernova has some things in common — a big boom, for example — there are plenty of different types. And different reasons why a star might go nova.

Even when focusing on one particular type of supernova, there's sometimes disagreement about what might be causing it. For example, it was thought that supernovae of type Ia had two possible parents driving them to destruction. But now, new data has allowed to astronomers to narrow down potential paternity.

Get ready for some daytime talk show-type antics, because the August 12 issue of Science reveals what kind of degenerates spawn a supernova Ia. This supernova happens when a white dwarf, a star too small to explode on its own, is part of a binary star system. Under certain circumstances, it can nab matter from its neighbor, building up enough matter to crush its center down to critical density and make it explode. But what type of star was letting its deadbeat companion steal all its precious matter?

There were two competing models, both rather judgmentally named. The single-degenerate model had the white dwarf stealing matter from a regular star, like the sun, or a star that had nearly exhausted its nuclear fuel but wasn't a white dwarf yet. The double-degenerate model has both stars as white dwarfs, with one of the two being more acquisitive.

Analyzing the explosions from the Ia supernovae, researchers found telltale traces of sodium. These were not from the novae themselves, but from the gases around the supernovae. Sodium gas might be around red giants, large stars whose outer layers are puffed up by the intense energy given off by the fusion in the center, but they aren't found around compact and mostly-burnt out white dwarfs.

And so it seems that only a single degenerate goes into forming these types of supernovae. Two white dwarfs, the data suggests, cannot make a nova.

Via Science, PBS and Nasa.