In the universe, a black hole that can devour all light and matter, like a mysterious shadow. For more than a hundred years, it has been “detected” by human beings, but it is always difficult to understand. Four years ago, the gravitational wave signals generated by the merger of two black holes were captured. Scientists converted gravitational waves into sound waves, and humans began to "listen" to black holes. Five months ago, astronomers from all over the world simultaneously announced the first black hole, and humans finally "see" the black hole.
Recently, humans have once again deciphered the black hole password. Researchers in the "Physical Review Letter" published that they "understood" the "sound" of a new black hole. It is also found that by analyzing the characteristics of this "sounding" mode, the quality and spin of the black hole can be obtained. This result is consistent with the mass and spin of the new black hole obtained by the analysis of the gravitational wave signal generated by other methods. It proves that Einstein's general theory of relativity is correct, and the black hole is the hairless theorem of the "bald giant". Also verified.
"Clock" contains black hole attributes
More than 100 years ago, Einstein's general theory of relativity predicted that if two black holes collided in the universe, they would merge to create a new black hole. After the birth, the "vibration", that is, the gravitational wave, is like a clock that is struck. The reverse sound waves are generated to propagate outward. However, more than 100 years later, the new black hole and the gravitational waves it produced are still a mystery, and have not been sneaked by humans.
On September 14, 2015, scientists first detected with the US Laser Interferometer Gravitational Wave Observatory (LIGO) that, in the 1.3 billion light years, two black holes were twisted and twisted together, radiating the quality of carrying black holes and The gravitational wave of the spin information. This event was named GW150914.
When the scientists eliminated the detector noise and amplified the gravitational wave signal, they observed a waveform that would increase rapidly before decaying. When they converted this signal into a sound, they heard a sound like "唧唧".
"The sound of the '唧唧' emitted by gravitational waves is a metaphor of image. Its waveform and sound waves are very similar." Liu Siming, chief scientist of the High-energy Particle Acceleration and Radiation Research Group of the Purple Mountain Observatory of the Chinese Academy of Sciences, said in an interview with the Science and Technology Daily.
In this exploration, the scientists determined that the gravitational wave was triggered by the combination of two giant black holes. The peak of the signal, the loudest part of the "beep" sound, is the moment when two black holes collide and merge into a new black hole.
In the following four years, scientists often detected gravitational wave events, but they have not been able to decode the properties of black holes.
Liu Siming made an analogy. "The gravitational waves generated by the new black holes generated by the merger of the two black holes are like the tail sounds after the bell. When the bell just rings, the sound is the loudest, and then gradually decays. The frequency of the tail sound and the size of the clock. Related, by analyzing the sound, you can reverse the quality and material of the clock.
Layers have different oscillation frequencies
Although the new black hole is likely to produce its own gravitational waves, the scientists believe that in the noise of the initial collision of the two black holes, its signal "sound" is too weak to be interpreted.
However, the research team found a new way to extract the "sound" of a black hole at the moment the signal reaches its peak. Through data simulation, the research team found that when the signal reaches its peak, there is also a “out-of-string sound”—a group of loud and short-lived “sounds”. When they took this "out-of-string sound" into consideration and re-analyzed the signal data, they found that they could successfully separate out a new "sound" mode, a "sound" from a new black hole.
The researchers applied this new technique to the actual observations of the GW150914. The analysis showed that there were at least one "off-of-chord" with lower frequency and faster attenuation in the few milliseconds after the peak of the signal, and two different In the "sound" mode, each "tone" and attenuation data comes from a new black hole.
Through numerical simulation, the scientists calculated the evolution process of gravitational waves, and then determined the mass and spin of the black hole. The scientists also used the "sound" characteristics of the signal peak to determine the mass and spin of the new black hole.
“We detected an overall gravitational wave signal consisting of multiple frequencies that gradually disappeared at different rates, just like the different pitches that make up the sound.” The first author of the paper, a researcher at the Massachusetts Institute of Technology in the United States Isey said, "Each frequency or tone corresponds to the vibration frequency of the new black hole."
Why do black holes emit gravitational waves of different vibration frequencies? Li Jinbin, an associate professor at Nanjing University of Aeronautics and Astronautics, introduced that the gravitational wave generated in the early stage of the merger of black holes is like throwing a stone into the lake. The shock of the stone forms different ripples on the lake surface. Different waves have different vibration frequencies. The initial oscillation is the most It is also the fastest and the fastest, and the energy delivered at this time is also the largest.
"Studies have been more research on the black hole when it is calmer. There are few studies on the initial stage of the merger. Part of the reason is that the scientists thought that the vibration of the strong gravitational wave is from a mixture of many nonlinear modes, which is difficult to analyze and extract. In the second study, the 'sound' is actually a linear superposition, and different vibration frequencies can be studied separately." Li Jinbin said.
"Pitch" and attenuation proof hairless theorem
In Einstein's view, a black hole with a certain mass and spin can only produce a specific "tone" and attenuation.
In this study, scientists used generalized relativistic equations to calculate the relationship between the attenuated gravitational wave signal and the mass and spin of the new black hole.
By comparing the observed data, the new black hole formed by the combination of two black holes weighs about 68.5 solar masses.
This result is consistent with the mass and spin data of the new black hole obtained by using the complete gravitational wave signal, and also verifies the "hairless" theorem of the black hole.
The famous American physicist John Wheeler predicted that black holes have only three observable characteristics, namely mass, spin and charge. The celestial bodies that form black holes, their "hairs", other features, should be swallowed up by black holes.
However, whether black holes have "hairs" has been debated by scholars for decades. Einstein also proposed a method to test this theory. When two black holes collide and form a new black hole, the gravitational waves generated cause ripples in space and time. The mass and spin properties of the new black hole should be encoded in Some of the "tones" of its gravitational waves.
The paper published this time supports the black hole "hairless" theorem and gives the "sounding" mode of the black hole. These calculations are consistent with previous measurements of black hole mass and spin.
"If the calculation results of scientists are significantly different from the measurement results, it means that the pattern of gravitational waves generated by black holes does not depend solely on mass, spin and charge. It also proves that the black hole 'hairless' theorem of general relativity prediction is wrong. On the contrary, this study proves that the specific frequency and attenuation rate of gravitational waves can be used to measure the quality and spin of black holes," said Liu Siming.
However, Li Jinbin believes that although this is the first experimental measurement to directly verify the "hairless" theorem, subject to the current observation, analysis tools and analytical capabilities, it does not mean that all black holes have no "hair".
Liu Siming believes that if there is a quantum effect, Einstein's theory may not be accurate enough. Just as Newton's theory of gravity is completely inapplicable when trying to describe the merger of black holes.
However, as LIGO resolution increases and more sensitive instruments come online in the future, researchers will be able to use this method to “hear” the “sound” of more new black holes.
"In the future, we will have better detectors in the Earth and space, and not only can see two, but also see dozens of patterns and accurately measure their properties." Isey said, "If these Not black holes, if they are more exotic objects like wormholes or boson stars, they may sound differently and we will have the opportunity to 'hear' them."