A highly explosive discovery that emerged from banning the bomb

The Biggest Bangs
September 19, 2003

The accidental discovery of cosmic gamma-ray bursts arose from the cold war paranoia of the 1960s and the need to monitor the Nuclear Test Ban Treaty.

The US launched a fleet of satellites called Vela . These could detect radiation from nuclear tests in space, to guard against the Soviets conducting clandestine tests in deep space or behind the Moon. The Los Alamos scientists operating the satellites never found any evidence of nuclear tests, but beginning in 1967, they detected several rapid and extremely powerful bursts of gamma rays, the most energetic type of electromagnetic radiation. They were able to determine that the bursts came from far beyond the vicinity of Earth. It was another six years before they published their observations. This caused a considerable stir among astronomers, but no generally accepted explanation could be agreed at the time.

The riddle took three decades to resolve, involved the construction and launch of one of Nasa's billion-dollar observatories, a lot of deep theoretical work and, in 1996, the launch of the Italian-Dutch Beppo-SAX satellite. Jonathan Katz, a theoretical physicist at Washington University in St Louis, US, was a participant in this quest and presents an entertaining exposition of the story of gamma-ray bursts from their discovery until 2002, when The Biggest Bangs went to press.

The picture often presented to the young tends to be that scientific discovery is an orderly progression from observation, to hypothesis testing, to generally accepted theory. Through Katz's account, we see that it often involves twists and turns, blind alleys, blunders, brilliant insights, agonies over budgets, fierce rivalries, and cut-throat competition for grants and priority of publication.

Katz shows why it was so difficult to reach a consensus that gamma-ray bursts were powerful explosions occurring in distant parts of the cosmos.

Part of the initial confusion was because there were really two different types of outburst being detected. One was a lower-energy repeating type taking place in our own galaxy, due to certain types of binary stars, and the other a much higher-energy class distributed randomly over the sky, indicating that they were located at cosmological distances. The observer's moment of greatest triumph was on January 23 1999, when an optical counterpart to a gamma-ray burst was detected and measured to reach an astonishingly bright ninth magnitude.

The final resolution remains incomplete, as the search for a theory to explain these great outbursts is still in progress. Likely candidates are supernova explosions of very massive stars, which form black holes as remnants rather than neutron stars, or a pair of merging neutron stars, or a neutron star being swallowed by a black hole. It may be that different types of bursts are due to different objects.

The author gives a lively account of science in action, written more as a detective story than as a textbook. The human side of science is presented along with lucid explanations of some aspects of high-energy physics. The technical and mathematical level demands a grasp of A-level physics, at least. It would, however, be excellent supplementary reading material for a university student taking a course in physics or astronomy, or as background material for their lecturers who may not be familiar with this subject.

Michael Dworetsky is director of the University of London Observatory, University College.

The Biggest Bangs: The Mystery of Gamma-Ray Bursts, the Most Violent Explosions in the Universe

Author - Jonathan I. Katz
ISBN - 0 19 514570 4
Publisher - Oxford University Press
Price - £14.99
Pages - 218

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