Astronomers are puzzling over a powerful cosmic explosion that seems to have detonated in a region of empty space, far away from any nearby galaxy. It may have been the death cry of a star that was born from debris strewn out of a past galactic dustup. Six spacecraft around Earth and Mars detected a powerful volley of gamma rays lasting about a minute on 25 January 2007. Such explosions, called long gamma-ray bursts, are thought to be caused when massive stars explode and their cores collapse into black holes. But follow-up observations by some of the world's most powerful telescopes failed to turn up any sign of a 'host' galaxy for the dying star. Spectral observations did show, however, that the burst, called GRB 070125, had exploded within a small pocket of dense gas.
Gamma Ray Explosion GRB 070125 Is A Cosmic Mystery A cosmic explosion that seems to have occurred thousands of light-years from the nearest galaxy-sized collection of stars, gas, and dust has puzzled astronomers. This "shot in the dark" is surprising because the type of explosion, a long-duration gamma-ray burst (GRB), is thought to be powered by the death of a massive star.
A team of astronomers has discovered a cosmic explosion that seems to have come from the middle of nowhere thousands of light-years from the nearest galaxy-sized collection of stars, gas, and dust. This "shot in the dark" is surprising because the type of explosion, a long-duration gamma-ray burst (GRB), is thought to be powered by the death of a massive star.
Image right: The robotic Palomar 60-inch telescope imaged the afterglow of GRB 070125 on January 26, 2007. Right: An image taken of the same field on February 16 with the 10-meter Keck I telescope reveals no trace of an afterglow, or a host galaxy. The white cross in this zoom-in view marks the GRBs location. The two nearest galaxies, and their distances, are marked with arrows. Credit: B. Cenko, et al. and the W. M. Keck Observatory. Tadpole HST.jpg + Click for larger image + Click for unlabeled version
"Here we have this very bright burst, yet it's surrounded by darkness on all sides. The nearest galaxy is more than 88,000 light-years away, and there's almost no gas lying between the burst and Earth" - Brad Cenko of the California Institute of Technology, Pasadena, Calif., lead author of the teams paper, which has been accepted for publication in The Astrophysical Journal.
The blast was detected on January 25, 2007, by several spacecraft of the Inter-Planetary Network. Observations by NASA's Swift satellite pinpointed the explosion, named GRB 070125 for its detection date, to a region of sky in the constellation Gemini. It was one of the brightest bursts of the year, and the Caltech/Penn State team moved quickly to observe the bursts location with ground-based telescopes.