LIGO Detected Gravitational Waves from Merging Black Holes

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On September 14, 2015 at 09:51 UTC, the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors located in Livingston LA and Hanford WA detected the first confirmed gravitational wave signal. Known as GW150914 (year 2015, month 09, day 14), the detected signal represented the merger of two orbiting black holes of 36 and 29 solar masses, forming a single black hole of 62 solar masses with 3 solar masses converted into energy that was radiated out as gravitational waves. From a redshift of z~0.1, we know that GW150914 occurred at a distance of approximately 1.3 billion light years away. Because of the twin LIGO detectors, which are like stereo microphones, we know the signal originated from an approximately 600 square degrees of the sky in the southern hemisphere near the Large Magellanic Cloud. Interestingly, the new Advanced LIGO detectors were just brought into operation for their first observing run when the signal was captured, suggesting there are more of these events than previously imagined.

Gravitational waves were predicted by Einstein’s General Theory of Relativity made 100 years ago (https://www.astronomyhouston.org/forum/ ... ?f=6&t=534). This event ushers the beginning of a new era of gravitational wave astronomy. All previous discoveries in astronomy have been light-based (i.e. electromagnetic spectrum – visible light, x-rays, radio waves, microwaves, etc).

Video of Press Conference: https://www.ligo.caltech.edu/detection

Press Kit: https://www.ligo.caltech.edu/system/med ... ss-kit.pdf

Science Summary: https://www.ligo.caltech.edu/system/med ... ummary.pdf

Educators Guide: https://www.ligo.caltech.edu/system/med ... -guide.pdf

Discovery Paper: http://link.aps.org/doi/10.1103/PhysRevLett.116.061102

Other Related Papers: https://www.ligo.caltech.edu/page/detec ... ion-papers

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Some Related Videos:

New York Times: http://www.nytimes.com/2016/02/12/scien ... stein.html

PHD Comics: https://www.youtube.com/watch?v=4GbWfNHtHRg

Thanks Debbie and Joe!

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Just to add, in my opinion, the most amazing aspect of this discovery is the impressive agreement between the measured waveform detected at the two LIGO sites and the expected waveform of two coalescing black holes as predicted by Einstein’s General Theory of Relativity, which seems to hold even in the non-linear regime of this violent cataclysmic event.

For historical purposes, I would like to add that we know gravitational waves exist and have observed them indirectly in the form of orbital decay of binary star systems. PSR B1913+16 is a binary pulsar-neutron star system first discovered in 1974 by Russell Hulse and Joseph Taylor. By timing the pulses from the Hulse-Taylor binary, we know that the system’s orbital period is gradually decreasing over time from the two neutron stars slowly spiraling into each other. The rate of energy loss from the inspiraling is exactly as predicted by Einstein’s theory in the form of gravitational waves. Although not observed directly, the orbital decay of PSR B1913+16 was the most convincing evidence at the time that gravitational waves exist. For that reason, Hulse and Taylor received the 1993 Nobel Prize in Physics.

According to Prof Alberto Vecchio, University of Birmingham and LIGO scientist, “We have observed the universe through light so far*, but we can only see part of what happens in the universe. Gravitational waves carry completely different information about phenomena in the universe. So, we have opened a new way of listening to a broadcasting channel, which will allow us to discover phenomena we have never seen before. This observation is truly incredible science and marks three milestones for physics: the direct detection of gravitational waves, the first detection of a binary black hole, and the most convincing evidence to date that nature’s black holes are the objects predicted by Einstein’s theory.”

* Not exactly true, as scientists have also been observing particles such as cosmic rays and neutrinos.

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As predicted, the 2017 Nobel Prize in Physics goes to Rainer Weiss, Barry C. Barish, and Kip S. Thorne "for decisive contributions to the LIGO detector and the observation of gravitational waves"

https://www.nobelprize.org/nobel_prizes ... press.html

https://www.nytimes.com/2017/10/03/scie ... ysics.html