Colliding white dwarfs give each other a new lease on life

White dwarfs are the ultra-dense husks of stars like our own, dying remnants that are just a pale shadow of their former glory. But when two white dwarfs come together, they can create something very special: a brand new star.

About 90% of all stars eventually become white dwarfs, which have nearly the mass of our Sun crammed into a sphere the size of Earth. Nobody knows quite how long white dwarfs can last before their fuel finally runs out - it could take trillions of years, if not several orders of magnitude longer than that, and our universe is only about 14 billion years old. But a pair of white dwarfs have revealed at least one other alternative, and that's full-on stellar rebirth.

Astronomers recently discovered the rather memorably named SDSS J010657.39–100003.3, which is a binary star system composed of two white dwarfs, one of which is 17% the Sun's mass, while the other is about 43%. The two orbit each other at a distance of just 140,000 miles, which is even closer than the distance between the Earth and the Moon. The two rotate each other at about a million miles per hour.

That's where things start to get really crazy - at those speeds, the stars complete a full revolution every 39 minutes, which is by far the fastest orbital time ever seen in a binary system. In fact, they're so close to each other that they actually warp the fabric of space-time between them. These spatial warps create energy discharges, which in turn force the stars ever closer. These two white dwarfs will soon collide.

Of course, "soon" is a relative term, particularly in astronomy - the stars aren't due to collide for another 37 million years. When white dwarfs collide, one of two things can happen: if the combined masses is greater than 140% of the Sun, the collision creates a supernova. But in this case, the white dwarfs will actually reignite nuclear fusion, creating a brand new star just like our Sun that will, after another few billion years of renewed life, cool down into yet another white dwarf.

This is the first time we've observed such a system, but the NASA astronomers who discovered this are certain there are many more like it in the solar system, some of which are likely due to collide far sooner than 37 million years in the future. Now it's just a question of finding them.

Monthly Notices of the Royal Astronomical Society via LiveScience. Artist's conception of white dwarf system by David A. Aguilar.