BBC Sky at Night Magazine

Gamma-ray burst afterglow seen across the Universe

It’s the most distant optical indication of a short burst ever detected

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The afterglow of one of the most intense explosions in the Universe – a short gamma-ray burst (SGRB) – has been spotted further away than ever before. A recent article announced the explosion was 10 billion lightyears away, meaning the blast occurred when the Universe was just 3.8 billion years old.

SGRBs are intense bursts of gamma radiation which flash across the Universe, believed to be produced by two neutron stars merging. They earn their ‘short’ moniker, however, as the optical component lasts only a few hours, leaving astronomer­s little time to catch this part of the outbursts before they fade away from view.

When astronomer­s received word on 22 November 2018 that an SGRB had been detected by NASA’s Neil Gehrels Swift Observator­y, they were able to remotely access the Gemini North telescope on Mauna Kea in Hawaii. Using this, they pinned down exactly which galaxy the burst came from.

“With SGRBs, you won’t detect anything if you get to the sky too late,” says Wen-fai Fong from Northweste­rn University, who took part in the study. “But every once in a while, if you react quickly enough, you will land on a beautiful detection like this.”

With the host galaxy known, the team were able to use the Gemini South telescope in Chile to pin down its distance at 10 billion lightyears away, meaning the blast dates from the Universe’s ‘teenage’ years.

“It’s long been unknown how long neutron stars – in particular those that produce SGRBs – take to merge. Finding an SGRB at this point in the Universe’s history suggests that, at a time when the Universe was forming lots of stars, the neutron star pair may have merged fairly rapidly,” says Fong. www.gemini.edu

 ??  ?? Distant light: the afterglow of SGRB181123­B (marked with a circle), as captured by the Gemini North telescope
Distant light: the afterglow of SGRB181123­B (marked with a circle), as captured by the Gemini North telescope

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