For physicists around the world, Christmas came one day late this year. On Dec. 26, scientists detected gravitational waves for a second time, further reinforcing Albert Einstein’s theory of general relativity.

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Kurt Hickman and Aaron Kehoe

By proving a hundred-year-old theory, an international team of scientists has taken another step toward understanding the birth and evolution of the universe.

The detection, announced today, was again made by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, which were built in part on a legacy of interdisciplinary technological advances made by Stanford scientists and engineers.

Like the first detection of gravitational waves, announced this past February, the event that triggered the later detection also came from the merger of two massive black holes. During this event – which is being called the “Boxing Day Event” – two black holes between eight and 14 times the mass of our sun merged together into a single, giant black hole.

As they circled and merged, they lost energy. More than one solar mass was converted to energy, which was radiated as ripples in “spacetime,” or gravitational waves, that began their journey 1.4 billion years before being detected by LIGO.

“Even for a physicist, the amount of energy released in one-tenth of a second is beyond comprehension,” said Robert L. Byer, the William R. Kenan, Jr. Professor of Applied Physics at Stanford, and an original member of the LIGO team.

For the scientists working on LIGO, the detection of a second event was a thing of joy – and relief.

“The observation of the second event was sweet because it confirmed the vision that the LIGO team had pursued for the past 20 years,” Byer said. “One event leaves the door open for questions about methods, calibration and likelihood of future events. The second event confirms those open questions and confirms the first step on the journey toward gravitational wave astronomy.”

The Stanford team continues to work to improve the sensitivity of the Advanced LIGO instruments and to devise ways to make future improvements even beyond Advanced LIGO.

“Our hope is to operate the LIGO sites as astronomical observatories,” said Brett Shapiro, a postdoctoral research fellow in the Department of Applied Physics. “This detection is important because it brings us closer to this goal of making regular astronomical observations.”

Current work will double the system’s sensitivity, which will increase the observation rate by about eight times, from one event per month to two events per week. Ultimately, this work will allow for the detection of fantastic cosmic events – such as neutron stars spiraling around each other – and the eventual confirmation of the details of Einstein’s theory of general relativity.

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Bjorn Carey, Stanford News Service: (650) 725-1944,