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Expert Available: Gravitational Waves from Second Pair of Black Holes

WHO: Gregory Harry, Associate Professor of Physics & LIGO Scientific Collaboration Member

WHEN: Ongoing

WHERE: Via phone, email, Skype, or at American University, 4400 Massachusetts Ave. NW., Washington, D.C.


On June 15, 2016, the Laser Interferometer Gravitational-wave Observatory, or LIGO, announced that a second pair of colliding black holes was detected. This follows the historic first detection of gravitational waves, announced earlier this year.

“This second detection of gravitational waves tells us that black holes are much more common in the universe than previously believed and clearly come together in pairs, which we don't completely understand. In addition, the black holes in this second event have lower masses than in the first detection. These lower masses allow for a stricter test of Einstein's theory of gravity, which once again is confirmed,” said Gregory Harry, associate professor of physics, American University. “Moving to the next observation run later in 2016, we can expect more events, which may include new astronomical phenomenon we are not currently aware of.”

LIGO uses lasers to precisely measure the position of mirrors separated from each other by 4 kilometers, about 2.5 miles. Gravitational waves, or ripples in the fabric of spacetime, produced by astronomical objects such as black holes, neutron stars, and supernova explosions cause these mirrors to move by a tiny fraction of the nucleus of an atom. The lasers detect the mirror's motion at observatories in Louisiana and Washington State. Near simultaneous detection in Louisiana and Washington of similar wave shapes is used to confirm that the mirrors’ motion was caused by astronomical gravitational waves.

On February 11, 2016, LIGO announced the historic first detection of gravitational waves, which had been predicted by Einstein 100 years earlier. The detection has been called the beginning of a new era in astronomy, when the universe can be studied using gravity as well as light. LIGO research is carried out by the LIGO Scientific Collaboration, a group of more than 1,000 scientists from universities around the United States and in 14 other countries.

About Professor Gregory Harry: Harry has been a member of the LIGO Scientific Collaboration for nearly 20 years and serves as the scientist responsible for research on the mirrors used in the current detectors. As part of the February 2016 announcement of the first detection of gravitational waves, Harry co-authored an op-ed in USA Today on the importance of federal funding for LIGO and science in general. Harry is currently researching new optical materials to be used in future upgrades of the LIGO detectors in an on-campus laboratory at American University. For more information about LIGO's detection of black hole pairs, visit


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