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Astronomers observe unusual light from a distant black hole

Cite Magazine

On 24 October 2012 a bright flash of light now known as Gamma-ray Burst 121024A was first detected by the Burst Alert Telescope on board the Swift satellite.

An artist’s impression of a Gamma-ray Burst, showing the two intense beams of relativistic matter emitted by the black hole. Credit: NASA/Swift/Mary Pat Hrybyk-Keith and John Jones.

Since the initial detection, an international team of astronomers has been able to observe something that no one has ever seen before – a polarised, bright flash of light from a dying star collapsing into a black hole. This extraordinary occurrence gives insight to an event that happened 11 billion years ago.

As the bright flash of light, also known asAs Gamma-ray Burst 121024A, occurred the astronomers were able to measure an unusual circular polarisation.

Curtin University’s own Dr Peter Curran was part of the team that viewed the Gamma-ray Burst.

Dr Curran said that the Gamma-ray Burst was “an unusual case, its light had strange features – it was circularly polarised.”

If light is polarised it means the waves are moving in a uniform way as they travel, in the case of circular polarisation that means the light corkscrews in a spiral motion.

“But the light from this Gamma-ray Burst looked like it was part of a 3D movie – it was about 1000 times more polarised than we expected,” says Dr Curran, “This means that the assumptions we’ve been making about Gamma-ray Bursts need to be completely reconsidered – assumptions of how electrons are accelerated to the incredible speeds we observe.”

Gamma-ray Bursts are emitted by dying stars collapsing to black holes that form jets of material travelling at over 99.995 per cent of the speed of light. They only last a fraction of a second, but in that time they send out as much energy as the Sun will in its entire life, making them the brightest objects in the entire Universe.




Further Information

Circular polarization in the optical afterglow of GRB 121024A” Wiersema, K et al. Published in Nature online