Scientists detect for the first time the ringing of a newborn black hole

If Albert Einstein's theory of general relativity remains true, then a black hole, born of the cosmic shaking collisions of two gigantic black holes, should itself "ring" as a result, producing gravitational waves very similar to those of a struck bell that reverberates the sound waves. Einstein predicted that the particular height and decay of these gravitational waves should be a direct signature of the mass and rotation of the newly formed black hole.

Physicists from MIT and elsewhere have "heard" the sound of a black hole for the first time and have discovered that the structure of this sound omen makes it the mass and rotation of the black hole – further proof that Einstein was right. all along.

The results, published today in Letters of physical examination, also favor the idea that black holes lack "hair" – a metaphor referring to the idea that black holes, according to Einstein's theory, should have only three observable properties: mass, spin and the electric charge. All the other features, which physicist John Wheeler called "hair," should be swallowed up by the black hole itself and would therefore be unobservable.

The findings of the team today support the idea that black holes are, in reality, hairless. The researchers were able to identify the ring pattern of a black hole and, using Einstein's equations, calculated the mass and spin that the black hole should have, depending on its ring pattern. These calculations corresponded to the measurements of the mass and the spin of the black hole carried out previously by others.

If the team's calculations were drastically discounted from the measurements, it would have suggested that the black hole ringtone coded for properties other than mass, spin, and electric charge – enticing evidence of physics beyond what the theory of Einstein can explain. But it turns out that the ring pattern of the black hole is a direct signature of its mass and rotation, thus confirming the idea that black holes are bald giants, devoid of superficial properties resembling hair.

"We all expect that the general relativity is correct, but it is the first time we confirm it in this way," said the study's lead author, Maximiliano Isi, NASA member Einstein Fellow of the Kavli Institute for Astrophysics and Space Research. "This is the first experimental measure that allows to directly test the theorem of the absence of hair. This does not mean that black holes can not have hair. This means that the image of hairless black holes still lasts a day. "

A tweet, decoded

On September 9, 2015, scientists performed the first-ever gravitational wave detection – infinitesimal, space-time ripples, emanating from far-off and violent cosmic phenomena. The detection, named GW150914, was performed by LIGO, the gravitational wave laser interferometer observatory. Once the scientists eliminated the noise and zoomed in on the signal, they observed a waveform that quickly accelerated before fading. When they translated the signal into sound, they heard something that sounded like a "chirp".

Scientists determined that gravitational waves were triggered by the rapid inspiration of two huge black holes. The peak of the signal – the loudest part of the chirp – is linked at the very moment when the black holes collided to merge into a single new black hole. Although this infantile black hole probably emitted its own gravitational waves, physicists assumed that its signature sound would be too weak to be deciphered amidst the sound of the initial collision.

However, Isi and his colleagues found a way to extract the reverberation of the black hole from the moments that immediately followed the peak of the signal. In previous work led by Isi's co-author, Matthew Giesler, the team had shown by simulations that such a signal, and in particular the part just after the top, contained harmonics ", a family of loud, short-lived sounds. When they reanalyzed the signal, taking into account the harmonics, the researchers discovered that they could successfully isolate a specific type of ringing at a newly formed black hole.

In the team's new paper, the researchers applied this technique to the actual data of the GW150914's detection, focusing on the last milliseconds of the signal, immediately after the peak of modulation. By taking into account the harmonics of the signal, they could discern a ring from the new black hole for baby. Specifically, they identified two distinct tones, each with a tone and a drop rate that they could measure.

"We detect a global gravitational wave signal composed of several frequencies that fade at different speeds, such as the different heights that make up a sound," explains Isi. "Each frequency or tone corresponds to a vibratory frequency of the new black hole."

Listen beyond Einstein

Einstein's theory of general relativity predicts that the pitch and decay of gravitational waves of a black hole should be a direct product of its mass and spin. That is to say that a black hole of a given mass and spin can only produce tones of a certain height and a certain decline. To test Einstein's theory, the team used the equations of general relativity to calculate the mass and spin of the newly formed black hole, depending on the height and decay of the two detected tones.

They found that their calculations corresponded to the measurements of the black hole mass and the rotation previously performed by others. According to Isi, the results demonstrate that researchers can actually use the strongest and most detectable parts of a gravitational signal to discern the ringing of a new black hole, whereas before, the Scientists assumed that this ring could only be detected inside the much darker end. of the gravitational wave signal, and only with much more sensitive instruments than what currently exists.

"It's exciting for the community because it shows that this type of study is possible now, not in 20 years," said Isi.

As LIGO improves its resolution and more sensitive instruments are connected 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 learn sounds that do not quite match Einstein's predictions, it could be an even more exciting prospect.

"In the future, we will have better detectors on Earth and in space, and we will be able to see not only two, but dozens of modes, and precisely define their properties," said Isi. "If they're not black holes like Einstein predicts, they're more exotic objects like wormholes or boson stars, they may not sound the same way and we'll be able to see."