Article by Phil Plait via Slate
I have long been fascinated by gamma-ray bursts (or GRBs). These are incredibly violent events: It’s like taking the Sun’s entire lifetime energy output and cramming into a single event that lasts for mere seconds! The energy emitted is so intense, so bright, we can see GRBs from a distance of billions of light years.
Gamma rays themselves are just a form of light, like the kind we see, but with huge energy; each photon is packed with millions or billions of times the energy in a single photon of visible light. Only the most energetic events in the Universe can make them, so if we detect a burst of them coming from the sky, we know something literally disastrous has happened.
We know GRBs come in many flavors. Some last literally for milliseconds, while others stretch on for minutes. We also know different events can cause them, too. Short ones seem to come from merging neutron stars, ultra dense compact objects left over after stars explode. The longer ones occur when massive stars explode, leaving their cores to collapse. In both cases, the huge blast of high-energy gamma rays signals the birth of a black hole.
But astronomers were recently surprised to find a third type of GRB, one that lasts not for minutes, but for hours. Whatever these objects are, they don’t just flash with light, they linger, blasting out far, far more gamma rays for far, far longer than was previously thought. What could do such a thing?
Several ideas were put forth, but new observations provided the linchpin: an ultra-long-duration GRB occurred on Christmas Day in 2010, and its distance was found to be a soul-crushing 7 billion light years away, about halfway across the visible Universe! This left only one possible candidate for the progenitor: a hugely massive star, one so big it dwarfs the Sun into insignificance.
