Findings

Stellar Explosion Illuminates Cosmic Dark Ages

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Science  09 May 2014:
Vol. 344, Issue 6184, pp. 565
DOI: 10.1126/science.344.6184.565-a
Lit up.

Hawaii's Subaru Telescope saw GRB 130606A.

CREDIT: ED DUNENS/FLICKR/CREATIVE COMMONS

A rare ultra–high-energy stellar explosion called a gamma ray burst (GRB) offers evidence that the "cosmic dark ages"—when no galaxies or stars illuminated the heavens—lasted at least a billion years after the big bang.

Post–big bang, the universe was filled primarily with neutral hydrogen gas. Light from the first stars and galaxies broke apart, or reionized, the hydrogen atoms. To find out when that happened, researchers look for abundances of neutral hydrogen in the universe's past.

One way to do this is to study GRBs, which occur when a large, rapidly rotating star collapses. The explosion shoots a beam of radiation into space; if pointed toward Earth, it appears as a flash of gamma rays, followed by an afterglow. Astronomers study this radiation to search for the absorption of telltale wavelengths of light by nearby neutral hydrogen.

Tomonori Totani, an astronomer at the University of Tokyo, and colleagues measured the spectrum of the afterglow from GRB 130606A, a very distant object that exploded when the universe was just 1 billion years old. Neutral hydrogen made up 10% of the intergalactic gas around the burst—suggesting that the reionization process that ended the dark ages was not yet complete, they report in a paper to be published in June in the Publications of the Astronomical Society of Japan. http://scim.ag/reionized

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