Caltech: First 'Overtones' Heard in the Ringing of a Black Hole

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Caltech: First 'Overtones' Heard in the Ringing of a Black Hole

Post by bystander » Wed Sep 11, 2019 8:56 pm

First 'Overtones' Heard in the Ringing of a Black Hole
California Institute of Technology | 2019 Sep 11

By listening for specific tones in the gravitational waves of black hole mergers, researchers are putting Albert Einstein's theories to new tests.

When two black holes collide, they merge into one bigger black hole and ring like a struck bell, sending out ripples in space and time called gravitational waves. Embedded in these gravitational waves are specific frequencies, or tones, which are akin to individual notes in a musical chord.

Now, researchers have detected two such tones for the first time in the "ringdown" of a newly formed black hole. Previously, it was assumed that only a single tone could be measured and that additional tones, called overtones, would be too faint to be detected with today's technologies. ...

The results, which were based on reanalyzing data captured by the National Science Foundation's LIGO (Laser Interferometer Gravitational-wave Observatory), have put Albert Einstein's general theory of relativity to a new kind of test. Because merging black holes experience crushing gravity, studies of these events allow researchers to test the general theory of relativity under extreme conditions. In this particular case, the researchers tested a specific prediction of general relativity: that black holes can be fully described by just their mass and rate of spin. Yet again, Einstein passed the test. ...

Scientists Detect Ringing of a Newborn Black Hole for the First Time
Massachusetts Institute of Technology | via physorg | 2019 Sep 11

If Albert Einstein's theory of general relativity holds true, then a black hole, born from the cosmically quaking collisions of two massive black holes, should itself "ring" in the aftermath, producing gravitational waves much like a struck bell reverbates sound waves. Einstein predicted that the particular pitch and decay of these gravitational waves should be a direct signature of the newly formed black hole's mass and spin.

Now, physicists from MIT and elsewhere have "heard" the ringing of an infant black hole for the first time, and found that the pattern of this ringing does, in fact, predict the black hole's mass and spin—more evidence that Einstein was right all along. ...

Testing the No-Hair theorem with GW150914 ~ Maximiliano Isi et al A Hierarchical Test of General Relativity with Gravitational Waves ~ Maximiliano Isi et al Black hole ringdown: the importance of overtones ~ Matthew Giesler et al
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