White Dwarfs Explode into Supernovae and Collide with Companion Stars

Scientists may have discovered how white dwarfs turn into Type Ia supernovae. While these white dwarfs transform into supernovae when they explode, researchers haven't been sure by what specific mechanism this occurs; now, they may have answers.

On May 3, 2014, researchers spotted a Type Ia supernova, designated iPTF14atg, in the nearby galaxy IC831, which is located 300 million light-years away from Earth. The data supported one of two competing theories at the origins of white dwarf supernovae, and suggested that there may be two distinct populations of these supernovae.

There are two competing origin theories for these supernovae, but they both start out the same. The white dwarf eventually explodes and is just one of a pair of stars. This interaction between these two stars is responsible for triggering supernova development. But what's the nature of this interaction? At this point, the theories diverge.

One is the double-degenerate model; this is when the companion to the exploding star is also a white dwarf, and the supernova explosion initiates when the two smaller objects merge. In the single-degenerate model, the second star is a sunlike star or red giant; the white dwarf's powerful gravity pulls material from the second star, which increases the temperature and pressure in the center of the white dwarf until a dramatic explosion occurs.

"My colleagues and I spent many sleepless nights on designing our system to search for luminous ultraviolet emission from baby Type Ia supernovae," said Yi Cao, one of the researchers, in a news release. "As you can imagine, I was fired up when I first saw a bright spot at the location of this supernova in the ultraviolet image. I knew this was likely what we had been hoping for."

In this case, the researchers saw a formation scenario consistent with the single-degenerate model. They witnessed an ultraviolet pulse that suggested that material ejected from a supernova explosion slams into a companion star, generating a shock wave that ignites the surrounding material.

The findings are published in the journal Nature.

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