Scientists detect tones in the ringing of a newborn black hole for the first time. Results support Einstein’s theory and the idea that black holes have no “hair.”
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 reverberates 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 studied the ringing of an infant black hole, 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.
The findings, published September 12, 2019, in Physical Review Letters, also favor the idea that black holes lack any sort of “hair” — a metaphor referring to the idea that black holes, according to Einstein’s theory, should exhibit just three observable properties: mass, spin, and electric charge. All other characteristics, which the physicist John Wheeler termed “hair,” should be swallowed up by the black hole itself, and would therefore be unobservable.
The team’s findings today support the idea that black holes are, in fact, hairless. The researchers were able to identify the pattern of a black hole’s ringing, and, using Einstein’s equations, calculated the mass and spin that the black hole should have, given its ringing pattern. These calculations matched measurements of the black hole’s mass and spin made previously by others.
If the team’s calculations deviated significantly from the measurements, it would have suggested that the black hole’s ringing encodes properties other than mass, spin, and electric charge — tantalizing evidence of physics beyond what Einstein’s theory can explain. But as it turns out, the black hole’s ringing pattern is a direct signature of its mass and spin, giving support to the notion that black holes are bald-faced giants, lacking any extraneous, hair-like properties.
“We all expect general relativity to be correct, but this is the first time we have confirmed it in this way,” says the study’s lead author, Maximiliano Isi, a NASA Einstein Fellow in MIT’s Kavli Institute for Astrophysics and Space Research. “This is the first experimental measurement that succeeds in directly testing the no-hair theorem. It doesn’t mean black holes couldn’t have hair. It means the picture of black holes with no hair lives for one more day.”
A chirp, decoded
On September 14, 2015, scientists made the first-ever detection of gravitational waves — infinitesimal ripples in space-time, emanating from distant, violent cosmic phenomena. The detection, named GW150914, was made by LIGO, the Laser Interferometer Gravitational-wave Observatory. Once scientists cleared away the noise and zoomed in on the signal, they observed a waveform that quickly crescendoed before fading away. When they translated the signal into sound, they heard something resembling a “chirp.”
Scientists determined that the gravitational waves were set off by the rapid inspiraling of two massive black holes. The peak of the signal — the loudest part of the chirp — linked to the very moment when the black holes collided, merging into a single, new black hole. While this infant black hole gave off gravitational waves of its own, its signature ringing, physicists assumed, would be too faint to decipher amid the clamor of the initial collision. Thus, traces of this ringing were only identified some time after the peak, where the signal was too faint to study in detail.
Isi and his colleagues, however, found a way to extract the black hole’s reverberation from the moments immediately after the signal’s peak. In previous work led by Isi’s co-author, Matthew Giesler of Caltech, the team showed through simulations that such a signal, and particularly the portion right after the peak, contains “overtones” — a family of loud, short-lived tones. When they reanalyzed the signal, taking overtones into account, the researchers discovered that they could successfully isolate a ringing pattern that was specific to a newly formed black hole.
In the team’s new paper, the researchers applied this technique to actual data from the GW150914 detection, concentrating on the last few milliseconds of the signal, immediately following the chirp’s peak. Taking into account the signal’s overtones, they were able to discern a ringing coming from the new, infant black hole. Specifically, they identified two distinct tones, each with a pitch and decay rate that they were able to measure.
“We detect an overall gravitational wave signal that’s made up of multiple frequencies, which fade away at different rates, like the different pitches that make up a sound,” Isi says. “Each frequency or tone corresponds to a vibrational frequency of the new black hole.”
Listening beyond Einstein
Einstein’s theory of general relativity predicts that the pitch and decay of a black hole’s gravitational waves should be a direct product of its mass and spin. That is, a black hole of a given mass and spin can only produce tones of a certain pitch and decay. As a test of Einstein’s theory, the team used the equations of general relativity to calculate the newly formed black hole’s mass and spin, given the pitch and decay of the two tones they detected.
They found their calculations matched with measurements of the black hole’s mass and spin previously made by others. Isi says the results demonstrate that researchers can, in fact, use the very loudest, most detectable parts of a gravitational wave signal to discern a new black hole’s ringing, whereas before, scientists assumed that this ringing could only be detected within the much fainter end of the gravitational wave signal, and identifying many tones would require much more sensitive instruments than what currently exist.
“This is exciting for the community because it shows these kinds of studies are possible now, not in 20 years,” Isi says.
As LIGO improves its resolution, and more sensitive instruments come online in the future, researchers will be able to use the group’s methods to “hear” the ringing of other newly born black holes. And if they happen to pick up tones that don’t quite match up with Einstein’s predictions, that could be an even more exciting prospect.
“In the future, we’ll have better detectors on Earth and in space, and will be able to see not just two, but tens of modes, and pin down their properties precisely,” Isi says. “If these are not black holes as Einstein predicts, if they are more exotic objects like wormholes or boson stars, they may not ring in the same way, and we’ll have a chance of seeing them.”
For more on this topic and a video simulation, see First Overtones Detected in the Ringing of a Black Hole as well as Einstein’s General Relativity Validated Years Ahead of Schedule.
Reference: “Testing the No-Hair Theorem with GW150914” by Maximiliano Isi, Matthew Giesler, Will M. Farr, Mark A. Scheel and Saul A. Teukolsky, 12 September 2019, Physical Review Letters.
This research was supported, in part, by NASA, the Sherman Fairchild Foundation, the Simons Foundation, and the National Science Foundation.
We see a cosmos that from our perspective requires that every possible clue is examined and that is what scientists are attempting to do. The problem we have is knowing what question we need to ask ourselves. I suspect that our universe is riddled with “Black Holes, rather like a Swiss cheese.” I also think that these black holes connect with alternate universes.What studies are being undertaken to discover what happens to the huge amounts of matter/energy being fed into these vortexes and where is it going? Somewhere there is a burp. Can anyone enlighten me? Also there is much study on how fast our universe is expanding. Please tell me, what ism the universe expanding into?
Problem with the multiverse theory is observables, in that there aren’t any we can verify. Second to that is people have a hard time believing what they can’t see, which is why many clever scientists still think black holes are a myth.
I agree with you, conservation of energy alone dictates the energy is neither lost or destroyed. I also don’t believe in singularities, these are the universal equivilent to dividing by 0 – showing the math is wrong.
Key thing is what we say is the visible universe, 3D+1T, I really doubt the universe has any limits, so not only can there be many pockets of 4D, but they are connected with something outside that 4D – and that is exactly what I think vacuum energy, dark matter and dark energy are. So black holes are matter spinning in dimensions other that visible universe, creating a one way aperture we can’t see the other end.
Anoying bit, is we can’t seem to find the white hole equivilent anywhere in the visible universe to confirm that idea.
The more I see about this ringing the more it reminds me of cavitation bubbles, which expand and contract until they reach equilibrium. I guess the analogy here is the Schwarzschild radius is what oscillates here, which would suggest the hole is more like an aperture and not full of matter.
Black holes ar not a one way aperture.. That’s a silly old myth. Facts established: We now know that these behave as giant cosmological vacuum cleaners. And like any household vacuum, it sucks in anything within range of its even horizon, BUT it alo ha to spit at the end… not swallow. What it sucks in through its 360º sides it spits out at very high pressure jets and X-ray energy from its top and bottom. MY CONJECTURE: This is acting to help homogenize the universe around it, purifying dead or dying planets or galaxies to prep it for make more planets later.