Summer 2004 -- Vol. 21

First Science Results Announced in Quest to Detect Gravitational Waves

The first scientific results have been reported from the most advanced scientific instrument ever built for detecting evidence of gravitational waves in the universe.

Lee Samuel Finn, professor of physics and professor of astronomy and astrophysics at Penn State, is one of the leaders in the development of the recently commissioned Laser Interferometer Gravitational-Wave Observatory (LIGO), whose first scientific results were presented at a meeting of the American Physical Society. Finn also is one of the world leaders in the effort to detect gravitational waves—vibrations caused by the interaction of objects in space.

“The commissioning has made such rapid progress that LIGO’s first data already have given us new science results, including new limits on gravitational radiation from such sources as inspiraling binary neutron stars, specific pulsars in our galaxy, and background radiation from the early universe,” Finn says. “While it is unrealistic to expect direct detections of gravitational waves during this initial phase of LIGO’s operation, we are eager to see what its future detections will reveal, as the instrument attains its full design sensitivity over the next couple of years.”

Predictions about when the first-ever direct detection of gravitational waves will take place depend on how frequently strong bursts of the waves bathe the Earth, which is something that scientists do not yet know and are looking to LIGO observations to reveal. Even as the initial LIGO detections are starting to reveal the characteristics of gravitational-wave signals, the LIGO Lab, the LIGO Scientific Collaboration, and their international partners are already proposing an advanced LIGO, with much greater sensitivity. “With the advanced LIGO, I am certain we will see gravitational-wave sources daily and will be able to use gravitational-wave detectors to study neutron stars and black holes in much the same way that astronomers use large telescopes today to study normal stars and galaxies,” says Finn.

Gravitational waves are intriguing to astronomers as a tool for peering through clouds of gas and dust to see directly into the core of collapsing stars, deep into the heart of colliding galaxies, and back to the earliest moments of the universe. Gravitational waves were first predicted by Albert Einstein in 1916 as a consequence of the general theory of relativity, which shows that alterations in the shape of concentrations of mass or energy have the effect of warping space-time, thereby causing distortions that propagate through the universe at the speed of light.

Finn is a founding member of the scientific collaboration that sets the science goals and carries-out the science mission of LIGO, which includes the detection of gravitational waves and their use as a new kind of telescope for viewing the universe. Finn supervised the development of much of the scientific data-analysis software for the LIGO project, sits on the LIGO Scientific Collaboration’s executive committee, and co-chairs one of the collaboration’s data-analysis groups. He also is director of the Physics Frontier Center for Gravitational Wave Physics, which was created by the National Science Foundation to develop the scientific and technical expertise needed to realize the promise of gravitational-wave detection. In addition, Finn is the director of the Penn State Center for LIGO Data Analysis, a major computing center under construction at Penn State dedicated to the analysis of LIGO data.

In addition to LIGO, with its three detectors located in Louisiana and Washington state, a similar device in Hannover, Germany—a German-U.K. collaboration known as GEO—is getting underway. LIGO and GEO are being used together as the initial steps in building a worldwide network of gravitational-wave detectors. “The more detectors the better,” says Finn. “Not only will our chances of seeing gravitational wave sources increase, but we will be able to learn more about each source we observe.”

The National Science Foundation has provided financial support for LIGO, and a collaboration between Caltech and MIT was responsible for its construction. A scientific community of more than 400 scientists from around the world, including Penn State, are now involved in research at LIGO.

Barbara K. Kennedy

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