​Spectacular Stellar Explosion Rewrites the Book on Gamma-ray Bursts

Earlier this year, astronomers detected one of the brightest explosions ever seen in space. Now, some seven months later, the unusual event has been confirmed as a gamma-ray burst — and it's changing the way we think about these cataclysmic explosions.

Called GRB 130427A, it's now officially the brightest gamma-ray burst (GRB) ever recorded. The event was chronicled on April 27 by the Large Area Telescope, the Gamma-ray Burst Monitor aboard the Fermi Gamma-ray Space Telescope, and other ground based telescopes.

It was a protracted explosion that lasted for an unprecedented 20 hours. The explosion produced 35 billion times the energy of visible light, and is about three times more powerful than the previous record.

​Spectacular Stellar Explosion Rewrites the Book on Gamma-ray Bursts

No doubt, GRBs are some of the most powerful explosions known to science — hyper-energetic blasts that result from the death of massive stars in distant galaxies. They're relatively rare, but this one happened a quarter of the way across the observable Universe, which is relatively close as far as these things go. The event offered astronomers a unique opportunity to study the little-known phenomenon, and to test our theories of physics under the most extreme circumstances.

NASA's animations of the gamma-ray burst:

NASA explains more:

Theorists believe that GRB jets produce gamma rays by two processes involving shock waves. Shells of material within the jet move at different speeds and collide, generating internal shock waves that result in low-energy (million electron volt, or MeV) gamma rays. As the leading edge of the jet interacts with its environment, it generates an external shock wave that results in the production of high-energy (billion electron volt, or GeV) gamma rays

Soon after this particular star exploded, it collapsed to make a black hole at its centre, producing a jet of matter that moved outward from the disaster scene at nearly the speed of light. The blast wave caused the rest of the star to expand outwards, generating a glowing shell of debris known as a supernova. As a result, astronomers have finally been able to confirm that the same object can simultaneously create both a powerful GRB and a supernova.

​Spectacular Stellar Explosion Rewrites the Book on Gamma-ray Bursts

Indeed, GRB 130427A is helping scientists think differently about the light and energy that's emitted immediately after these explosions. While scanning the initial 20-hour burst, the astronomers were able to study the "afterglow," including X-ray, optical, and radio wavelengths. They were also able to take a close look at the energies of the photons emitted by the GRB.

The subsequent analysis of this data, which now appear in four different studies published in Science, has upturned the standard model of GRB emissions.

For example, scientists used to think that the initial burst of light from GRBs was produced through synchrotron radiation (electromagnetic radiation produced when charged particles are accelerated radially). But observations of GRB 130427A shows that the high-energy photons detected were simply too powerful to have resulted from this process. It's a discovery that puts a new constraint on the nature of gamma-ray bursts.

It's worth noting that events like these can sterilize huge swaths of intergalactic space — regions spanning thousands of light-years.

Read the studies at Science: Here, here, here, and here.

Image: NASA/Swift/Cruz deWilde and NASA/DOE/Fermi LAT Collaboration
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