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Mystery behind fireball after gamma ray burst revealed

Washington: NASA's Hubble Space Telescope has discovered that short-duration gamma ray bursts are produced by the merger of two small, super-dense stellar objects. 
The evidence is in the detection of a new kind of stellar blast called a kilonova, which results from the energy released when a pair of compact objects crash together. 
Hubble observed the fading fireball from a kilonova last month, following a short gamma ray burst (GRB) in a galaxy almost 4 billion light-years from Earth. 
A kilonova had been predicted to accompany a short-duration GRB, but had not been seen before.
"This observation finally solves the mystery of the origin of short gamma ray bursts," Nial Tanvir of the University of Leicester in the United Kingdom, said. 
Tanvir lead a team of researchers using Hubble to study the recent short-duration GRB. 
"Many astronomers, including our group, have already provided a great deal of evidence that long-duration gamma ray bursts (those lasting more than two seconds) are produced by the collapse of extremely massive stars. But we only had weak circumstantial evidence that short bursts were produced by the merger of compact objects. This result now appears to provide definitive proof supporting that scenario," Tanvir said. 
A kilonova is about 1,000 times brighter than a nova, which is caused by the eruption of a white dwarf. 
The self-detonation of a massive star, a supernova, can be as much as 100 times brighter than a kilonova. 
Gamma ray bursts are mysterious flashes of intense high-energy radiation that appear from random directions in space. 
Short-duration blasts last at most a few seconds, but they sometimes produce faint afterglows in visible and near-infrared light that continue for several hours or days. 
The afterglows have helped astronomers determine that GRBs lie in distant galaxies. 
Astrophysicists have predicted short-duration GRBs are created when a pair of super-dense neutron stars in a binary system spiral together. 
This event happens as the system emits gravitational radiation, creating tiny waves in the fabric of space-time. 
The energy dissipated by the waves causes the two stars to sweep closer together. In the final milliseconds before the explosion, the two stars merge into a death spiral that kicks out highly radioactive material. 
This material heats up and expands, emitting a burst of light. 
The research is published online in the journal Nature. 

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