Cosmic mystery: The robotic Palomar 60-inch telescope imaged the afterglow of GRB 070125 on 26 January 2007. The white cross marks the GRB’s location. The two nearest galaxies, and their distances, are marked with arrows.
Credit: B. Cenko, et al. and the W. M. Keck Observatory.
SYDNEY: A massive cosmic explosion in a barren section of the universe has left astronomers totally perplexed.
"Here we have this very bright burst, yet it's surrounded by darkness on all sides," says Brad Cenko of the California Institute of Technology, Pasadena, U.S., lead investigator behind the find. "The nearest galaxy is more than 88,000 light-years away, and there's almost no gas lying between the burst and
Earth."
The explosion was a long-duration gamma-ray burst, called long-duration because it lasted longer than two seconds. Until now, astrophysicists thought these explosions came from the death of a young, massive star. Massive stars similarly require a large amount of gas a dust, which are usually found in bright galaxies.
Empty space
But according to a new study reporting the find to be published in the Astrophysical Journal, the explosion occurred in a region where there is no gas or other matter.
"Big stars live fast and die young, without much time to move around," says astronomer and co-author Derek Fox, of Pennsylvania State University. "So if this massive star died far away from any galaxy, the key question is, how did it manage to be born there?"
The explosion was detected on 25 January 2007 by the Inter-Planetary Network, a group of spacecraft with gamma-ray burst detectors, and was one of the most powerful bursts detected this year. Astronomers pinpointed the explosion to the constellation Gemini and named it GRB 070125. From its spectrum, they could tell the explosion actually took place more than 9.4 billion years ago - about 5.4 billion years before the Earth came into existence.
Astronomers also found that the explosion had a fast-fading afterglow in the visible light, so watched it with two large telescopes – Gemini North telescope and Keck 1 telescope, both in Hawaii. Usually this visible light would be absorbed by the dense gas and dust that typically surrounds stars.
But in this case, nothing had absorbed any of the light. Telescope images revealed a lack of galaxies in the region surrounding the explosion.
"Quite puzzling"
"We should see… [gamma-ray bursts] in galaxies full of stars. But this one appears to have no obvious galaxy at that location. This is quite puzzling," commented Joss Bland-Hawthorn, an astrophysicist at the University of Sydney in Australia. "I suspect that there are many more surprises to be had like this one. We have so little understanding of the high energy universe," added Bland-Hawthorn, who is not one of the study's authors
There is a possibility that the two closest galaxies – 88,000 and 150,000 light years from the explosion – interacted with each other sometime ago, leaving behind the star that caused this gamma-ray burst. If this is the case, the researchers hope to capture more detailed pictures of the area with the Hubble Space Telescope to prove it.
"It's possible the source is in a very small galaxy, as they were common at those times. Big galaxies today are assembled from smaller galaxies in the past," said Bland-Hawthorn.
Gamma-ray bursts are one of the great mysteries of the universe - always making astronomers go back to the drawing board. Previous detections have forces them to accept that gamma-ray bursts may come from the edges of faint galaxies, accompanied by an unimpressive supernova (see, Cosmic explosion from nowhere, Cosmos Online) However, this is the first time they have detected a gamma ray burst in a region of the universe so completely devoid of matter.
