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.

Disk fragmentation is one of two competing theories for why close-companion formation happens. In this scenario, a single, massive disk of gas and dust surrounding a newborn star becomes unstable and breaks apart. Eventually, it coalesces into another star right next door.…