Feuding white dwarf stars have been destroying each other for millions of years

Over a thousand light-years from Earth, there are two white dwarfs, the ghostly remnants of stars much like our Sun. But these stars aren't ordinary white dwarfs, and their bizarre composition reveals a long, passive-aggressive history of mutually assured destruction.

Most white dwarfs are composed of carbon and oxygen, the result of billions of years of completing burning away the original star's hydrogen and helium fuel. And yet both of these stars are composed primarily of helium, according to new research by Steven Parsons and Professor Tom Marsh of the University of Warwick. That's highly unusual, and it means something odd must have happened as these stars began to die and transition into being white dwarfs.

What most likely happened is that the more massive of the two stars was the first to die, and it began to expand into a red supergiant much as our own Sun will five billion years from now. But its companion star didn't give it enough room to expand, ripping off its outer hydrogen envelope and stopping it the midst of its evolution. Because of this, the star was left as a husk of helium, and it collapsed back into a helium white dwarf.

And then, in the cosmic equivalent of revenge, the newly minted white dwarf did exactly the same thing to its companion star when it too began to expand. Now the two are locked in a quite literal death spiral, as their mutual orbits bring them closer and closer together. In about a billion years, the two stars will collide into each other and merge into a single star known as a hot subdwarf, which will run for about a hundred million years. And then, at long last, these two stars can die a natural death.

Via Astrophysical Journal.