It appears a close binary system — a pair of stars orbiting so close they were touching — has finally merged into a single stellar object, producing an enormous flash of light in the process. The pair, called V1309 Sco, was observed by astronomers to briefly reach a luminosity 10,000 times greater than normal (30,000 times more luminous than the Sun) before settling back down to its normal brightness. Astronomers believe the unusual flash corresponded to the moment when the two stars merged — the first time such an event has been directly observed.
It is not known how common such close pairs are, but multiple-star systems of larger separation are quite common. This vid features animation (apparently using real data) showing the orbits of several known binary star systems.