What Makes White Dwarfs Go Supernova?
published during a waxing gibbous moon.
10/12/2016

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A Type 1a supernova as seen by Hubble on the outskirts of a disc galaxy. Credit: NASA, ESA, The Hubble Key Project Team, and The High-Z Supernova Search Team

There are plenty of things that set off an explosion–a detonator, a wick, or even just the wobbling of a mostly dead star known as a white dwarf, which literally goes supernova when it ignites.

A recent paper published in the Monthly Notices of the Royal Astronomical Society puts forth a new mathematical model proposes that white dwarves going supernova is all down to the wobble of the white dwarves as they near the end of their life.

When a white dwarf, the cooling remnant of an old star, explodes into a supernova, it can create a bright light known as a Type Ia supernova.

“Type Ia supernovae are extremely important objects in physics, best known for their role in revealing that the expansion of the universe is accelerating,” Saavik Ford, a co-author of the paper said in a statement. “The problem is that people do not agree on exactly how Type Ia supernovae come to be.”

So what is it, exactly that causes a white dwarf to blow its top? Previous research looked into how a binary star system with at least one white dwarf might start a Type Ia supernova when the stars collided.

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Supernova Formation Graphic: One (older version) of how white dwarves in a binary system might go supernova. Credit: NASA, ESA and A. Feild (STScI)

In some cases, especially when the other star is not a white dwarf, the explosion is so large that it can send the other star hurtling out into space.

But there are far more Type Ia supernovae than there are binary white dwarf systems where the two objects are close enough to each other to actually collide. For all their high density, white dwarfs are only about the size of Earth, and having two of them run into each other in the vastness of space would be difficult without taking into account other forces.

In this case, the researchers think that the wobble is to blame. White dwarfs wobble or oscillate as they orbit each other. That motion can cause one white dwarf in the system to tug on its companion, eventually causing the white dwarf to lose its cool one way or the other.

“Basically, we’ve proposed that if you have two white dwarfs spiraling towards each other and you shake one of them the right way for long enough, one will either blow up or you’ll bring the objects closer together faster for an eventual detonation,” co-author Barry McKernan said.

McKernan, Ford, and other researchers hope to be able to test their theories by observing white dwarfs with future gravitational wave sensors, like the planned LISA gravitational wave detector.