Sallyport - The Magazine of Rice University - Spring 2002

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Through The Sallyport Spring 2002 VOL.58, NO.3 Celestial Milestones At the dawn of humankind, the known universe ended at the horizon. These days, astronomers are looking into the farthest reaches of space. But just how far is that? ........................................................................... This small matter of distance isn t simply an academic point. In astronomy, distance equals time, and knowing how far away celestial objects are not only can provide insight into their makeup but can help answer fundamental questions about the origin, evolution, and nature of the universe. So far, undisputed means to accurately calibrate universal distances have eluded scientists, but Rice researchers Edison Liang and Dan Kocevski and collaborator Brad Schaefer at the University of Texas at Austin think they might be on the right track. Fondren Library Fondren Library is pleased to announce that its new website is now online. Upcoming refinements to the site will include a search engine and a text-only version of the homepage. The answer may be hidden in the celestial phenomenon of gamma-ray bursts transient, short flashes of gamma rays that occur randomly in the sky every day. Gamma rays themselves cannot be seen by human eyes, but they can be detected by instruments in orbit. About 3,000 gamma-ray bursts have been recorded, mostly during the 1990s, and since 1997, scientists have known that these bursts represent gigantic explosions likely associated with the death of massive stars at a distance of about 10 billion light years. This makes gamma-ray bursts excellent candidates to serve as guideposts for astronomers hoping to trace the formation of massive stars and the structure and evolution of the early universe if the exact distances to the bursts can be determined. But astronomers know the actual distance to only a very few. Two methods have been proposed in recent years for indirectly calculating the distance from available data, and now, Liang, Kocevski, and Schaefer have come up with a third. It s well-known that gamma-ray bursts start at high energy and evolve to lower energies, says Liang, the Andrew Hays Buchanan Professor of Astrophysics. We examined 16 gamma-ray bursts and found that the apparent rate at which the burst is cooling off appears to be directly related to the distance of the burst, provided that the rate is measured not in terms of time, but in terms of the total number of gamma rays emitted since the beginning of the pulse. The technique works, however, only with gamma-ray bursts that have distinctly separate pulses, or peaks, of intensity. Most bursts have multiple peaks of energy, and the overlapping data of these multiple peaks make it difficult to estimate the true cooling rate of the highest peak. You tend to underestimate the cooling rate when observing bursts with multiple peaks, notes Kocevski, a graduate student in the Department of Physics and Astronomy. http://www.rice.edu/sallyport/2002/spring/sallyport/celestialmilestones.html (1 of 2) [10/30/2009 10:56:12 AM]
Through The Sallyport Liang and his colleagues are trying to develop methods to separate the data of the overlapping pulses to determine the true cooling rate. They are hopeful that they will eventually be able to calculate the distance of any gamma-ray burst, expanding the database of knowledge from which deductions about the formation of the early universe can be made and providing new insights into the physical mechanisms of these enigmatic explosions. The group presented its findings at a meeting of the American Astronomical Society in Washington, D.C., on January 7. Images of gamma-ray bursts used for this study, which was supported by NASA, can be found at http://www.kocevski.com. B. J. Almond [ back to top ] Featured Stories | Through the Sallyport | On the Bookshelf | Who's Who Students | Arts | Scoreboard | Yesteryear | Previous Issues Copyright ©2002 Rice University http://www.rice.edu/sallyport/2002/spring/sallyport/celestialmilestones.html (2 of 2) [10/30/2009 10:56:12 AM]
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