LIGO’s Second Detection: By The Numbers

On December 26, 2015, scientists observed gravitational waves—ripples in the fabric of spacetime—for the second time.

The gravitational waves were detected by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington. The LIGO observatories are funded by the National Science Foundation and were conceived, built, and are operated by Caltech and MIT.

The discovery, accepted for publication in the journal Physical Review Letters in June, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.ligo_waves3

The second discovery “has truly put the ‘O’ for Observatory in LIGO,” says Caltech’s Albert Lazzarini, deputy director of the LIGO Laboratory. “With detections of two strong events in the four months of our first observing run, we can begin to make predictions about how often we might be hearing gravitational waves in the future. LIGO is bringing us a new way to observe some of the darkest yet most energetic events in our universe.”

  • Physicists have concluded that these gravitational waves were produced during the final moments of the merger of two black holes—14 and 8 times the mass of the sun—to produce a single, more massive spinning black hole that is 21 times the mass of the sun.
  • The merger occurred approximately 1.4 billion years ago.
  • The detected signal comes from the last 27 orbits of the black holes before their merger.
  • The Livingston detector measured the waves 1.1 milliseconds before the Hanford detector.
  • LIGO research is carried out a group of more than 1,000 scientists from universities around the United States and in 14 other countries.

On the Grounds

birdbathAccording to Caltech’s Architectural Heritage by Romy Wyllie, this marble bird bath was purchased in London and given to the geology division in 1939 by Harvey S. Mudd, who later served as a vice president of the Board of Trustees at Caltech. He was the son of mining engineer and philanthropist Seeley W. Mudd, for whom the Seeley W. Mudd Laboratory of the Geological Sciences (North Mudd) is named, and brother to Seeley G. Mudd—a onetime cancer researcher at Caltech—for whom the Seeley G. Mudd Building of Geophysics and Planetary Science (South Mudd) is named. So it’s only fitting that this sculpture sits in the small courtyard on the eastern side of the building named for Harvey Mudd’s father.

A Holiday Homecoming

The Juno spacecraft, which launched on August 5, 2011, finally arrived at Jupiter on July 4. The JPL-managed mission will, for the first time, peer below Jupiter’s dense cover of clouds to answer questions about the gas giant and the origins of our solar system. Juno’s primary goal is to reveal the story of Jupiter’s formation and evolution by observing Jupiter’s gravity and magnetic fields, and atmospheric dynamics and composition. To learn more about the mission, go to

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