Hubble’s greatest discoveries: the cause of gamma-ray bursts

The Hubble Space Telescope saw the ‘smoking gun’ that revealed the secrets of these enormous cosmic explosions.

GRB 130603B © © NASA, ESA, and Z. Levay (STScI/AURA)
An infrared glow was spotted on 13 June 2013 (left) but had faded by 3 July (right) © NASA, ESA, and Z. Levay (STScI/AURA)

This fuzzy-looking galaxy was home to one of the most energetic events in the Universe: a gamma-ray burst (GRB). These flashes of gamma-ray radiation are an enigma because they’re so rare – a typical galaxy produces only a few every million years. Yet they release as much energy in a few seconds as our Sun does in 10 billion years.

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On 3 June 2013, a GRB lasting one-tenth of a second occurred, and was spotted by NASA’s Swift satellite. When the Hubble Space Telescope looked 10 days later, it found an infrared glow where the burst had been. But by 3 July it had faded.

This disappearing glow was the dying embers of another kind of cosmic explosion – a kilonova – believed to be the result of extremely dense stars called ‘neutron stars’ merging. Since the kilonova was found in the same location as the GRB, it was the ‘smoking gun’ revealing that short GRBs could well be caused in the same way.

The kilonova was investigated by Prof Nial Tanvir of Leicester University, who says Hubble played a vital role. “Although Swift discovered this particular short gamma-ray burst, and observations from ground-based telescopes gave us its precise position and distance, Hubble was the only option for seeing the faint kilonova emission.”

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