On Christmas Day 2010, NASA's Swift satellite detected a massive, sustained gamma-ray burst whose cause still leaves astronomers baffled.
Aurore Simonnet, NASA E/PO, Sonoma State University
The Christmas sky last year was lit up by an extraordinarily powerful and mysteriously long-lasting explosion in space that scientists now suggest was a comet smacking into a dense star or a peculiar supernova death.
Radiation from gamma-ray bursts, the most powerful explosions ever seen in the universe, strikes Earth's atmosphere from random directions in space about twice a day. These bursts can be roughly divided into two kinds, ones lasting less than two seconds, and ones lasting up to minutes.
Scientists think shorter gamma-ray bursts are generally caused by merging neutron stars — dead stars made up of super-dense neutron matter. Longer bursts are typically thought to originate from hypernovas, in which giant stars that explode as incredibly powerful supernovas spew two opposing jets of energy as they die; we see them head-on as bursts. [Photos of Great Supernova Explosions]
However, researchers suspect a number of mysterious events of completely different origins could mimic gamma-ray bursts. Such might be the case with the Christmas burst, formally known as GRB 101225A.