How Do Close Binary Stars Form?

Our Sun is a bit of an outlier in the general stellar population. We typically think of stars as being solitary wanderers throughout the galaxy. But roughly half of Sun-like stars are locked in with more than one companion star. If there are two, it’s known as a “binary” system, but in many cases there are even more stars all collectively tied together by gravity. Astronomers have long debated why this happens, and a new paper, available in pre-print on arXiv from Ryan Sponzilli, a graduate student at the University of Illinois, makes an argument for a mechanism known as disk fragmentation.