Gamma-ray bursts are the most powerful, most luminous explosions in the universe. From Earth, these cosmic explosions are manifested as an extremely bright flash of gamma radiation quickly followed by an also-incredibly-bright afterglow, observable at all other wavelengths from x-ray to optical to infrared to radio. The brightest afterglow to date was visible to the naked eye.
On June 7th, another record-smashing gamma-ray burst occurred, detected from orbit by NASA's Swift satellite. This event, known as GRB 080607, was just as powerful intrinsically as 080319B, - but was nowhere near bright enough to be seen visually, for two reasons. First, it was quite a bit further away: 11.5 billion light years, corresponding to an era in which the universe was only a few billion years old. Second, and much more interestingly, the afterglow was nearly hidden behind a thick cloud of gas and dust within the galaxy in which the GRB was born.
Astronomers were able to come to this conclusion not by looking at the galaxy directly, but from the study of the afterglow itself. UC Berkeley associate professor of astronomy Joshua Bloom and graduate students Daniel Perley and Adam Miller were observing with the Keck I telescope in Hawaii at the moment the burst occurred, and were able to quickly slew the 10-meter telescope - one of the largest in the world - to the newly identified afterglow position within a few minutes. Using the telescope to take a spectrum of the optical afterglow, they were able to record hundreds of features imprinted upon the light of the afterglow as it passed through, and was selectively absorbed by, gas and dust in its host galaxy. Jason X. Prochaska at the University of California at Santa Cruz and Yaron Sheffer at the Ohio State University have identified hundreds of these features as corresponding to various elements and molecules - some of which have never been seen at the immense distance (and, therefore, as early in the universe's history) which this burst occurred, and measured dozens of additional features which have never been observed in astonomical, or perhaps even a laboratory, context at all. In addition, supplementing the visible spectrum with measurements from the infrared telescope PAIRITEL, the team was able to measure the extent to which the gas and dust had dimmed the optical light: by well over a factor of 100! Had this event been a little closer and without its dust screen, it may have been visible in the sky to the naked eye for a few seconds. However, the distance and the dust screen, and their inferences about the nature of the chemical makeup of the early universe, are what make this event truly one-of-a-kind to date.
Page authored by D. Perley (University of California, Berkeley)
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