Hubble Pinpoints Optical Counterpart of Gamma Ray Burst in a
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Hubble Pinpoints Optical Counterpart of Gamma Ray Burst in a Distant Galaxy

February 8, 2005
This is a false-color Hubble Space Telescope image of the visible fireball which accompanied the gamma ray burst called GRB 970228. This is the first optical image ever taken which associates a gamma-ray burst source with a potential host galaxy. This observation provides strong supporting evidence that gamma-ray bursts are cosmological- they originate in distant galaxies across the universe.

The burst was detected on February 28, 1997. The Hubble picture is a combination of two images taken on March 26 and April 7, with the Wide Field Planetary Camera 2 (in planetary camera mode).

The arrow points to the fireball, which is a white blob immediately to the upper left of image center. Immediately to the lower right of center is an extended object (roughly resembling an "E") interpreted to be the host galaxy where the gamma-ray burst is embedded. A follow-up image taken on April 7 showed the fireball had faded, but not the extended source, supporting the interpretation it is a host galaxy at great distance.

It may be a significant finding that the fireball is offset from the center of the galaxy. This rules out a supermassive black hole that could be at the galaxy's core, as the source of the gamma-ray burst. A more likely explanation is that the burst came from the titanic collision of two neutron stars, or a neutron star with a stellar-mass black hole, in the disk of the galaxy.

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