The observed events were so unusual astronomers couldn't even agree on what to call them; suggestions ran from supernova imposters to intermediate-luminosity red transients.
Now scientists say they know what causes them and that cause has even provided a name, the Los Angeles Times reported Friday.
Writing in the Journal Science, astrophysicists say the events are caused when two stars temporarily orbit so close together that they share a "common envelope," or veil, of gases.
Some closely orbiting stars will simply merge, they said, but at other times a pair of stars will violently eject the superheated gas that surrounds them.
The result, they say, is a "common envelope event" that results in the bright cosmic spectacle.
Such events can last from weeks to hundreds of years in duration, lead study author Natalia Ivanova, an astrophysicist at the University of Alberta in Canada, said.
Either time frame is considered extremely brief in a cosmic context, the researcher said.
"The short time scale for such events suggests that we would never directly observe them," they wrote.
In fact it is only recently that such events have been observed.