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Dr. Donald Lamb
Professor, Department of Astronomy and Astrophysics, University of Chicago, Chicago
Donald Lamb is the Louis Block Professor in the Department of Astronomy and Astrophysics at the University of Chicago and the Enrico Fermi Institute. His current interests include gamma-ray bursts, supernovae and galaxy clusters. He is the author of more than 300 papers and the coeditor of several books on theoretical astrophysics. He has made seminal contributions to stellar structure and evolution, especially the structure and evolution of white dwarfs and neutron stars, compact X-ray sources and gamma-ray bursts. He helped found and continues to play a significant role in the ambitious Sloan Digital Sky Survey. Prof. Lamb is Mission Scientist for the High-Energy Transient Explorer (HETE-2); a Swift satellite associate scientist; and Director of the DOE ASC / Alliance Flash Center at the University of Chicago.His paper from 2000 with Daniel Reichart, "Gamma-Ray Bursts as a Probe of the Very High Redshift Universe" predicted the existence of gamma-ray bursts such as GRB 050904, the topic of NASA's September 12 press teleconference.
Slide above: Discovery of the first very high redshift GRB opens the door to their use as unique and powerful probes of the early universe. The slide places GRBs in cosmological context and highlights what very high redshift GRBs can tell us about the early universe.
At recombination, which occurs at redshift z = 1100, the universe becomes transparent. The cosmic background radiation originates at this redshift. Shortly afterward, the temperature of the cosmic background radiation falls below 3000 K and the universe enters the ``dark ages,'' during which there is no visible light in the universe. ``First light,'' which cosmologists think occurs about z = 20, corresponds to the moment when the first stars form. Ultraviolet radiation from these first stars and from the stars that are born later is thought to re-ionize the universe. Afterward, the universe is transparent in the ultraviolet. GRBs are due to the collapse of massive stars, and are therefore expected to occur out to redshifts of about z = 20 (unlike QSOs or bright galaxies). Both GRBs and their afterglows are very bright, and are therefore easily observed out to z = 20 (unlike QSOs or galaxies).
As the light from each GRB afterglow travels to us, it passes through intergalactic gas and galaxies at lower redshifts. These leave their "fingerprints" on the light, telling astronomers about the history of the universe in a way that is analogous to the way that ice cores drilled deep into the Greenland ice cap tell us about the climatic history of the Earth. In particular, very high redshift GRBs are:
o markers of the moment of "first light," o tracers of the star-formation history of the universe,
o tracers of the elemental abundance history of the universe, and o tracers of the reionization history of the universe.
Thus GRBs hold enormous promise as unique and powerful probes of the early universe.
Image credit: Dr. Don Lamb and Dr. Daniel Reichart