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Pomona College Professor Helps Solve 30-Year Space Mystery

In the 1960’s military satellites discovered incredibly bright, extremely brief flashes of light originating somewhere in deep space. While the origin of some gamma ray bursts was solved in the 1990s, a large group of very short, hard bursts remained mysterious until now.

Bryan Penprase, a Pomona College associate professor of physics and astronomy and director of Pomona’s Brackett Observatory, is a co-author of an article in the journal Nature, that solves the question. By locating two short bursts and combining optical, xray and radio data in new ways, the research group concluded that the short, hard GRBs resulted from colliding neutron star that coalesce into a black hole..

The article is "The Afterglow of GRB050709 and the Nature of the Short-Hard Gamma-Ray Bursts," Nature, 437, 845-850, October 6, 2005. The CalTech research team, of which Penprase is a member, is lead by Shrinivas Kulkarni.

“What makes gamma ray bursts exciting,” explains Penprase, “is that they have the potential for lighting up parts of the universe that have never been studied, galaxies from what is some times called the ‘Cosmic Dark Ages,’ before more conventional stars formed.”

When stars from distant, primeval galaxies explode, the burst of light takes an instantaneous snapshot in the same way that a flashbulb can do of its surroundings.

“Studying GRBs is really the study of the archeology of the universe by looking at the fossil light that’s traveled billions of years through space,” says Penprase. “By studying a few photons that come at us from that early time, we can exactly watch how things were back then. We’re looking at galaxies as they actually were in a way that no other subject allows.”

In addition to direct observation, Penprase is also studying the spectra of GRBs, a more subtle technique examining the environment around the GRB. By analyzing GRB spectra absorption lines, Penprase and the research team can figure out the different elements and their abundances, their temperatures and densities and to find out what the galaxies are like. With Edo Berger, of the Carnegie Observatories of Pasadena, Penprase is analyzing the light spectra for GRB50505, one of the earliest and most distant GRB explosions that has been studied so far.

Student Max Wainwright ’07 has been working with Penprase and Berber to compile an atlas of space galaxies that host gamma ray bursts. The project involved using the Hubble Space Telescope to develop a complete catalog of the galaxies in which the gamma ray bursts exploded.

One of the main conclusions is that the galaxies seem to show more asymmetry and departures from their radial profiles than typical galaxies, which are usually more quiescent and self-gravitating galaxies. “It’s an amazing thing he’s pulled off,” says Penprase, who also notes that Wainwright is the first author on a paper submitted to the Astrophysical Journal.

Penprase, along with Pomona College Professor Alma Zook and students Rachel Paterno-Mahler ‘07 and Gordon Stecklein ’08, with others, was also a co-author of the article “Deep Impact: Observations from a Worldwide Earth–Based Campaign,” Science, 14 October 2005. Remotely operating Pomona’s one-meter telescope on Table Mountain, the Pomona Group tracked the Deep Impact satellite and comet Tempel 1. On impact, they took photos every few seconds and compiled a light curve of the brightening of the comet after impact.

Pomona College, one of the nation’s premier liberal arts institutions, offers a comprehensive program in the arts, humanities, social sciences and natural sciences. Its hallmarks include small classes, close relationships between students and faculty, and a range of opportunities for student research.