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Cottrell Scholar Plays Key Role in Gravity Wave Confirmation

Joshua Smith, a Cottrell Scholar from Cal State Fullerton, has been conducting gravitational-wave research for the last 15 years. He was involved in a major way in the confirmation of the existence of gravity waves, which was announced this week.

Smith, an associate professor of physics, is director of the Cal State Gravitational-Wave Physics and Astronomy Center.

“Through the support of RCSA, I have studied the quality of LIGO optics,” Smith says. “In particular, I have worked to improve the astrophysical range of LIGO by measuring and understanding the sources of optical scattering.”

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is designed to detect gravitational waves predicted by Einstein’s General Theory of Relativity. LIGO’s multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves from cataclysmic cosmic sources such as the mergers of pairs of neutron stars or black holes, or by supernovae. LIGO consists of two widely separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana—operated in unison to detect gravitational waves.

Smith’s efforts will be key to increasing the rate of gravity wave detection going forward.

He has been working to identify and reduce sources of transient noise, within timescales similar to LIGO’s September detection of the merger of binary black holes announced this week. The merger took place roughly 1.3 billion light years from Earth, and released gravitational radiation that was an estimated 50 times greater than the total output power of all the stars in the observable universe.

“Reducing transient noise is key for LIGO to be able to clearly distinguish binary black hole signals from the background noise and to accurately estimate their source parameters,” Smith notes.

He and his students have used statistical techniques and data analysis to help pinpoint the sources of transient noise, and they have worked with LIGO observatory staff to fix these issues.

Building on this experience, Smith led efforts to validate the GW150914 event, announced this week, through a deep characterization of the detectors. “When we discovered GW150914, we immediately embarked on a months-long follow-up of the instrument status and performance, and a check of all internal and external recorded signals,” Smith said. “The candidate signal passed these tests with flying colors, being consistent with a gravitational wave in every way.”

In other words: Einstein was right again.

Smith worked on these LIGO projects with Cal State Fullerton colleagues Geoffrey Lovelace and Jocelyn Read, both assistant professors of physics, and both recipients of RCSA funding.


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