Gravitational Waves Detected Again (video)


Pair of colliding black holes send signal from 1.4 billion years ago

The Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration, which includes Georgia Tech researchers, and the Virgo collaboration have observed a second gravitational wave event.

The observation was made in the early morning hours (UTC) of December 26, 2015. It is smaller than the initial, historic detection made in September 2015, but was also produced by a pair of colliding black holes.

Gravitational waves, or ripples in the fabric of spacetime, carry information about their origins and the nature of gravity that cannot otherwise be obtained. Physicists say the December waves were produced during the final moments of the merger of two black holes—14 and eight times the mass of the sun—to produce a single, more massive spinning black hole that is 21 times the mass of the sun. LIGO estimated the September black holes were 29 and 36 times the mass of the sun.

“It is very significant that these black holes were much less massive than those observed in the first detection,” said Gabriela Gonzalez, LIGO Scientific Collaboration spokesperson. “Because of their lighter masses compared to the first detection, they spent more time—about one second—in the sensitive band of the detectors. It is a promising start to mapping the populations of black holes in our universe.”

The signal was detected by both of the twin LIGO detectors located in Louisiana and the state of Washington.

During the merger, which occurred approximately 1.4 billion years ago, a quantity of energy roughly equivalent to the mass of the sun was converted into gravitational waves. The detected signal comes from the last 27 orbits of the black holes before their merger.

“Once again, the collaborative work of hundreds of scientists and engineers has allowed us to pull the curtains and peek into the new window of the universe that was opened last September,” said Laura Cadonati, Georgia Tech professor and chair of LIGO’s data analysis council. “We now have two strong signals from merging black holes and we are now excitingly awaiting for more discoveries to come in the next months as the detectors improve and our analysis is robust.”

Cadonati is one of 12 Georgia Tech faculty members, postdoctoral researchers and students in the LIGO Scientific Collaboration. The team continues to develop tools and techniques to detect, analyze and characterize sources from the first science run of Advanced LIGO, including this second event.

“With this second discovery of a binary black hole merger, we begin to unveil a population of black holes in the universe,” said Professor Deirdre Shoemaker, director of Georgia Tech’s Center for Relativistic Astrophysics and a member of LIGO. “This hints at the excitement to come as we probe deeper into the sky, listening to the story gravity is telling us about the universe.”

The first detection of gravitational waves, announced on February 11, 2016, was a milestone in physics and astronomy. It confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity and marked the beginning of the new field of gravitational-wave astronomy.

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. More than 90 universities and research institutes in the LSC, including Georgia Tech, develop detector technology and analyze data. Approximately 250 students are strong contributing members of the collaboration.

The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built and are operated by Caltech and MIT. The new discovery, accepted for publication in the journal Physical Review Letters, 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.


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