Blast From Empty Space Poses Mystery

Dec. 19, 2007 -- Just when space scientists thought they had solved the mystery of the brightest explosions in the universe, along comes one that has the experts befuddled.

The confounding "gamma ray burst" was detected by space-based instruments and the Swift orbiting gamma ray observatory on Jan. 25, 2007. At first it stood out only because it was rather bright -- one of the brightest ever recorded. Since then, however, the burst -- dubbed GRB 070125 -- has proven far more interesting in other ways.

Unlike the other hundred or so similar gamma ray bursts discovered -- most of which shine out momentarily with incredible brightness from crowded stellar nurseries -- GRB 070125 appears to be all by itself in space without any signs of a galaxy around it. That goes against everything astronomers have learned about gamma ray bursts over the last ten years.

"It's out in the middle of nowhere," said gamma ray burst investigator Derek Fox of Pennsylvania State University. Fox coauthored a report on GRB 070125 that will be published in The Astrophysical Journal.

The current theory holds that gamma ray bursts like GRB 070125 are given off by super-jumbo-sized stars that run out of fuel and violently collapse to form black holes, explained Neil Gehrels, principal investigator of NASA's Swift telescope.

Such huge stars can only be created in very gas and dust-rich parts of galaxies where lots of other stars are also being born. So it makes no sense to find such a star living and dying in the empty space between galaxies. Nor is there time for such stars to travel out into intergalactic space, said Gehrels, since mega stars are also the shortest-lived.

The mystery of GRB 070125 only deepened as astronomers narrowed in on the burst's location, about 9.5 billion light-years away, with more powerful telescopes. They were still looking for the light from the galaxy which theory predicted must be there, but no galaxy appeared.