They've been a mystery ever since they burst onto the cosmic scene several years ago -- short-lived, red eruptions that burned brighter than novas, yet dimmer than supernovas.
Not only were astronomers hard pressed to explain what caused these newly observed events, they couldn't even agree on what to call them. They've been dubbed variously as supernova imposters, V838 Mon-like events, and intermediate-luminosity red transients, or ILRTs.
Now, scientists say they may have solved the mystery.
In a paper published Thursday in the journal Science, astrophysicists say the events bear the signature of two stars that temporarily orbit so close together that they share a "common envelope," or veil of gases.
In some instances, the close-orbiting stars will merge. But in other cases, scientists theorize, the stars will violently eject the superheated gas that surrounds them. The result, they say, is a "common envelope event."