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NASA’s Hubble solves mystery of the origin of short gamma ray bursts

Strong evidence from NASA’s Hubble Space Telescope lends support to the theory that short-duration gamma ray bursts are produced from the merging of two small, super-dense stellar objects.

The proof came with the detection of a new stellar blast, called a kilonova. A kilonova occurs when a pair of compact objects crash together, releasing a burst of energy. Hubble observed one such energy release last month, subsequent to a short gamma ray burst (GRB) in a galaxy 4 billion light-years from Earth. It has long been predicted that a kilonova would accompany a short-duration GRB, but this is the first time anyone has witnessed such an event.

Nial Tanvir, from the University of Leicester, led a team of researchers to study the short-duration GRB. There has been a great deal of evidence that long-duration GRBs, lasting longer than two seconds, originate from the collapse of extremely massive stars, but only weak circumstantial evidence that short bursts were the result of a merger of weak objects. This study seems to provide definitive proof for this scenario, the results of which appeared in a special online edition of the journal Nature over the weekend.

GRBs are flashes of intense high-energy radiation, appearing from random directions in space. Short-duration blasts last only a few seconds, but they can produce faint afterglows that continue for several hours or even days. These afterglows have helped researchers establish that GRBs lie in distant galaxies.

Researchers have predicted that short-duration GRBs are created when, in a binary system, two super-dense neutron stars spiral together as the system emits gravitational radiation, which creates tiny waves in the fabric of space-time. Energy dissipated by the waves causes the two stars to move closer together. Just before the explosion, the pair of stars merge into a final spiral, kicking out highly radioactive material that heats up and expands before emitting a burst of light.

A recent paper from the University of California at Berkeley presented new calculations predicting how kilonovas should look. On June 3, an opportunity to test this model arrived when NASA’s Swift space telescope picked up an extremely bright GRB. From June 12-13, Hubble searched for the location of the initial burst, eventually spotting a faint red object. Independent analysis of the data confirmed the detection. Subsequent observations revealed the source had faded away, thus providing key evidence that the infrared glow was the product of an explosion accompanying the merger of two objects.

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