Cannibal Supernova Eats Companion Star

Simulation of Type 1a supernova slamming into a companion star, courtesy of Daniel Kasen via Caltech

Omnomnom. Astronomers have seen a signal from an exploding white dwarf that indicates it is consuming its unlucky companion star. 

A robotic sky-observer, intermediate Palomar Transient Factory (iPTF), was used to observe the supernova explosion, called iPTF14atg, which is 300 million light-years away. The telescope looks for objects in the sky that vary in brightness over time, including supernovae.

After tirelessly endeavoring to come up with a system to search for specific luminous signals emitted from supernovae, Caltech graduate student Yi Cao and his colleagues were justifiably elated when data finally started pouring in. "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," Cao said in a statement. 

The ultraviolet signal that Cao describes occurs when an exploding white dwarf slams into a companion star. The impact creates a shock wave that ignites everything that's unfortunate enough to be in the vicinity of the explosion. This sudden energy emits an equally sudden burst of very energetic ultraviolet radiation. This burst is quite short and easy to miss, so Cao and his team were understandably pumped to spot it, especially since that part of the sky had been unremarkable just the night before. 

The data collected from this event gives scientists an exciting opportunity to predict how supernovae form. Currently, there are two opposing theories about the formation of this sort of supernova, called a Type 1a supernova. They both have the same origins story, starting with a white dwarf and another star orbiting each other. The powerful gravitational attraction of the white dwarf causes the pair to interact. This triggers a supernova in the white dwarf, but the nature of this interaction is up for debate. 

In one theory, known as the "double-degenerate model," the other star is also a white dwarf. The supernova explosion occurs when these two stars merge and create an immense amount of energy.

In the other theory, called the "single-degenerate model," the other star is a sun-like star or a red giant. Either way, this enormous star has plenty of matter to spare in its outer layers of gas. The white dwarf sucks up these outer layers of gas with its powerful gravitational pull. Eating all of this star-food makes the white dwarf quite hot and bothered; the pressure builds up as the white dwarf continues to gorge itself on the outer layers of its companion star. Eventually, the pressure is too much and the white dwarf violently vomits in a Type 1a supernova. 

The evidence collected by iPTF supports the single-degenerate model, the one where the white dwarf binges on a companion star and belches up the remains in a colossal explosion.

Shrinivas R. Kulkarni, a Caltech astronomy and planetary science professor, commented that the discovery "provides direct evidence for the existence of a companion star in a Type Ia supernova, and demonstrates that at least some Type Ia supernovae originate from the single degenerate channel."

The findings were published in the journal Nature.

[Via NatureCaltech]

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