Since its launch in 2008, the Fermi space telescope has recorded hundreds of gamma-ray bursts (GRBs), flashes of light that, for just a few seconds or minutes, are the brightest objects in the Universe. And now the telescope is yielding data that is starting to explain the mechanisms that unleash these beam-like jets of light, which are thought to emanate from the poles of a spinning star as it collapses to form a black hole and explode in a supernova.
On 7 May, at the 2012 meeting of the Fermi/Swift GRB conference in Munich, Germany, members of the Fermi team showed evidence that the gamma rays were not being generated through the commonly invoked process of synchrotron radiation, where electrons emit light as they are accelerated in shockwaves rippling out from the explosion. Instead, most of the light is coming from a seemingly more obvious place: originating in thermal emissions at the surface of the fireball. Just as the Sun’s yellow light emanates from its photosphere (the surface region from which the externally perceived light of a star originates), so too are the GRBs arising mostly as thermal emissions from the photosphere of a fireball expanding at nearly the speed of light.
“It’s a big paradigm shift because everyone thought it was synchrotron radiation for 20 years,” says Jochen Greiner, an astronomer at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and one of the leaders of the team in charge of the GRB monitor on Fermi.
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