What happens when two stars fall into each other?

The universe is mostly empty, but once in a great while stars get close enough to crash into each other. Two stars recently combined to form Sco V1309. Find out what happened when they did.

In 2008, two stars became one, only no one knew it yet. All anyone knew was a previously unknown star sent up a bright enough flash to get noticed by astronomers. They named it Sco V1309 and proceeded to debate what on earth it was doing to make it flare that dramatically. It was only after they had combed back through old observations of that area of the sky that they found evidence for the stellar marriage.

Looking back over thousands of images they saw a slight variation of light in Sco V1309's section of the sky. This variation came from the light given off by two stars circling each other. They had to be very close together, in fact, pretty much touching. The timing of the variation showed that they circled over a period of one and a half days. Over the years, this do-si-do shortened as the stars speeded up and got even closer together. The outer layers of the stars merged.

As the two stars strained closer, the circling variation stopped, and the star started just getting brighter. It doubled in brightness every 19 days until the middle of 2008, when it brightened itself 300 times over in about ten days. Quite a show, but it took the merging of the cores, when the star became 30,000 times brighter than our own sun, to finally get people to notice the match. Congratulations, newly formed Sco V1309! All those who wish to honor the match, throw rice at the sky tonight.

[Via Science News. Image Credit: NASA]