An odd celestial explosion recorded two years ago has been confirmed as the brightest supernova ever identified. It is so bright that scientists are still scrambling to explain it.
The explosion, called SN 2005ap, was discovered on 3 March 2005 by Robert Quimby as part of the Texas Supernova Survey, a project he led at the University of Texas in Austin, US, before moving to Caltech in 2007.
Just how intrinsically bright the explosion was did not become clear until recently, when follow-up observations traced the violent event to a distant galaxy 4.7 billion light years from Earth.
To appear as bright as it did from that distance means SN 2005ap was intrinsically twice as bright as the previous record holder, SN 2006gy, which Quimby also discovered as part of the same supernova survey.
Quimby suggests that two factors combined to make SN 2005ap the brightest known supernova. First, the object emitting the light was very large. He thinks this could have been a large shell of material that the star had thrown off well before the explosion. The shell then heated up and glowed brilliantly when it was hit by the blast wave from the explosion.
Second, the explosion itself was probably unusually powerful. Quimby speculates that it was a gamma-ray burst (GRB), the violent birth cry of a black hole or neutron star that accompanies the collapse of a massive star's core.
GRBs form when some of the matter falling onto the central black hole or neutron star gets shot out violently in jets travelling at close to the speed of light.
When pointed right at Earth, such jets send bursts of gamma-rays our way. In this case, however, the jets may not have been pointed at us, explaining why gamma-ray telescopes did not observe the event.
Quimby says the event shows that the universe still has lots of surprises to throw at us. With so many great astronomers having combed the skies for so long, "you get to the point where you think, 'How am I going to do something new?" he told New Scientist. "But it turns out that the universe is so vast and so wondrous that there's much more left to be found."
Journal reference: The Astrophysical Journal, (in press)
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