Gamma-ray bursts are the most powerful (and mysterious) explosions in the universe, shooting massive concentrated jets of hot plasma that are way too powerful to come from an ordinary supernova. And they might be the birth pangs of black holes.
Astronomers have observed gamma-ray bursts for nearly fifty years. We still don't know much about their origins. Here's what we know for certain: after a star dies, matter can be churned up around its remains and blasted away with amazing force, in the process emitting massive amounts of radiation. If the jet happens to be pointed towards Earth, we can observe the event, which looks an awful lot like a regular supernova...except on an order of magnitude that would be totally impossible for an ordinary supernova.
The leading explanation for these gamma-ray bursts, or GRBs, was that they were caused by magnetars, ultra-dense neutron stars that spin quickly enough to create incredibly powerful magnetic fields. In that theory, the magnetic field is responsible for concentrating the matter in two huge clumps around the magnetar's poles, then blasting the two jets away. But there's an upper limit to how powerful those blasts could be, and analysis of four recent GRBs shows they were all much too powerful to be caused by magnetars.
That leaves only one possible explanation: black holes. As black holes form from the husk of collapsed stars, they could also gather together the surrounding matter and create massive jets. Because black holes can be of any size, they could create jets of any possible force. That means black holes could create these mysteriously powerful GRBs. This would likely only occur as the black holes are first forming, meaning GRBs are a sign that a new black hole has emerged.
This doesn't necessarily replace the magnetar model - if anything, it relieves a lot of pressure that was being placed on that theory to explain overly powerful GRBs. It's definitely still possible that somewhat weaker gamma-ray bursts are caused by magnetars - after all, the theoretical framework for magnetars creating GRBs is still sound - but the really massive gamma-ray bursts appear to be the exclusive domain of baby black holes.