"We really think we’ve found this new class of gamma-ray bursts and a natural explanation for creating them in a type of star collapse that we haven’t previously talked about," said Andrew Levan, an astronomer at the University of Warwick in Coventry, England, who led a study on the phenomena.

Gamma-ray bursts are the brightest explosions in the universe, shooting out powerful blasts of high-energy light, and they typically signal the death of a massive star collapsing to form a black hole.

Up until now, scientists have classified gamma-ray bursts as short (typically less than two seconds) and long (typically 20 to 50 seconds, with some lasting up to a few minutes).NASA’s Swift satellite, launched in 2004, swivels around when it detects some high-energy activity to catch these fleeting events before their light disappears.

But these strange ultra-long bursts that Swift has documented in the last few years can last hours -- 100 times longer than those stellar flashes in the pan, said Bruce Gendre of the French National Center for Scientific Research.