Gamma-ray burst offers first peek at young galaxy’’s star factory

January 7th, 2009 - 1:01 pm ICT by ANI  

Washington, Jan 7 (ANI): The brilliant afterglow of a powerful gamma-ray burst (GRB) has enabled astronomers to probe the star-forming environment of a distant galaxy, resulting in the first detection of molecular gas in a GRB host galaxy.
The explosion, designated GRB 080607, occurred in June last year.
“This burst gave us the opportunity to ”taste” the star-forming gas in a young galaxy more than 11 billion light-years away,” said University of California, Santa Cruz, professor Xavier Prochaska.
The finding provides insight into star formation when the universe was about one-sixth its present age.
Gamma-ray bursts - the universe’’s most luminous explosions - create bright afterglows. Their light encodes information about the gas and dust it encounters on its way to Earth.
“We clearly see absorption from two molecular gases: hydrogen and carbon monoxide. Those are gases we associate with star-forming regions in our own galaxy,” Prochaska said.
The team believes that the burst exploded behind a thick molecular cloud similar to those that spawn stars in our galaxy today.
Swift calculated the burst’’s position, beamed the location to a network of observatories, and turned to study the afterglow.
That night, University of California, Berkeley, professor Joshua Bloom and graduate students Daniel Perley and Adam Miller were using the Low Resolution Imaging Spectrometer on the 10m Keck I Telescope in Hawaii.
“Because afterglows fade rapidly, we really had to scramble when we received the alert,” Perley said. “But in less than 15 minutes, we were on target and collecting data,” he added.
A pair of robotic observatories also responded quickly.
The NASA-supported Peters Automated Infrared Imaging Telescope (PAIRITEL) on Mount Hopkins, Arizona, and the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory on Mount Hamilton, California, observed the burst’’s afterglow within three minutes of Swift’’s alert.
The spectrum from Keck established that the explosion took place 11.5 billion light-years away. GRB 080607 blew up when the universe was just 2.2 billion years old.
The molecular cloud in the burst’’s host galaxy was so dense, less than 1 percent of the afterglow’’s light was able to penetrate it.
“Intrinsically, this afterglow is the second brightest ever seen. That’’s the only reason we were able to observe it at all,” Prochaska said.
Screening from thick molecular clouds provides a natural explanation for so-called “dark bursts,” which lack associated afterglows.
“We suspect that previous events like GRB 080607 were just too faint to be observed,” said team member Yaron Sheffer of the University of Toledo, Ohio.
Nearly half of the absorption lines found in the Keck spectrum are unidentified. The team expects that understanding them will provide new data on the simplest space molecules. (ANI)

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