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December 9, 2003

Neutron Stars May Merge More Often Than Thought

The pulsar and its companion star merging. The merged object may become a black hole. (Credit: John Rowe Animation)

EVANSTON, Ill. --- A recent discovery of a double neutron-star system has helped to increase astronomers’ chances at collecting the information they need to better understand the black holes and neutron stars in our Galaxy.

Neutron star pairs may merge and give off a burst of gravitational waves about six times more often than previously thought, scientists report in the Dec. 4 issue of the journal Nature. If so, the current generation of gravitational-wave detectors might be able to register such an event every year or two, rather than about once a decade -- the most optimistic prediction until now.

Gravitational waves were predicted by Einstein’s general theory of relativity. Astronomers have indirect evidence of their existence but have not yet detected them directly.

The revised estimate of the neutron-star merger rate springs from the discovery of a double neutron-star system, a pulsar called PSR J0737-3039 and its neutron-star companion, by a team of scientists from Italy, Australia, the United Kingdom and the United States using the 64-m CSIRO Parkes radio telescope in eastern Australia.

Vicky Kalogera, assistant professor of physics and astronomy at Northwestern University, is a member of the international team. She, along with her graduate student Chunglee Kim and colleague Duncan Lorimer from the University of Manchester, used the characteristics of the newly discovered pair of neutron stars to calculate how many more such pairs exist in our Galaxy. Next, they calculated that first-generation gravitational wave detectors, like LIGO in the United States, should be able to detect the merger of neutron stars once every year and a half.

“We know gravitational waves exist, but only from indirect evidence,” said Kalogera. “Once we can detect the gravitational waves from these merger events directly, we will have an amazing new window into the cosmos. We will learn a great deal more about relativity and the properties of astronomical objects such as neutron stars and black holes.”

Marta Burgay, a Ph.D. student at the University of Bologna in Italy is lead author on the Nature paper. Kalogera’s portion of the research was supported by the National Science Foundation’s gravitational physics program and the David and Lucile Packard Foundation.