The gravitational wave detector LIGO / Virgo has discovered a black hole with 142 times the mass of the sun. This is the first time that astronomers have observed a medium mass black hole, and it is also the largest black hole observed by gravitational wave. < / P > < p > this black hole is formed by the combination of two black holes with mass of 85 times and 65 times of solar mass respectively, which also challenges the current black hole formation theory, because the theory predicts that a black hole with 85 times the mass of the sun is impossible to exist. < / P > < p > the findings, published today in Physical Review Letters and Astrophysical Journal Letters, will help us better understand the supermassive black holes in the center of some galaxies. < / P > < p > the seemingly empty universe is actually filled with the echo of gravitational wave string sound. Gravitational waves are produced by extreme astrophysical phenomena, which ripple in time and space, just as the bell in the universe transmits sound. This time, the researchers heard a loud noise. < / P > < p > this event is the largest black hole merger event observed using gravitational waves. The 142 times solar mass black hole formed by this event is also the first medium mass black hole to be clearly detected (i.e., a black hole with a mass of 100 to 1000 times the mass of the sun). The black hole is a combination of two black holes with mass of 85 times and 65 times of the sun mass, which challenges the current black hole formation theory: according to the current theory, a black hole with 85 times the mass of the sun cannot exist. < / P > < p > the gravitational wave signal was detected by the laser interference gravitational wave observatory (LIGO) in the United States and the Virgo interferometer in Italy on May 21, 2019, so the researchers named it gw190521. Today, LIGO and Virgo team of scientists published two papers in international journals to report the research results of signal pair. One was published in Physical Review Letters, describing the discovery process of gravitational wave signals in detail; the other was published in the Astrophysical Journal Letters, discussing the physical properties and astrophysical significance of signals. Previously, all black holes observed by astrophysicists can be divided into two categories: stellar black holes and supermassive black holes. The mass of a stellar black hole is several to dozens of times the mass of the sun, which is generally believed to be formed after the death of a massive star; while the mass of a supermassive black hole reaches hundreds, thousands, or even billions of times that of the sun, and there is one such black hole in the center of the galaxy. However, the final mass of the black hole releasing this gravitational wave signal is 142 times the mass of the sun, which is between the stellar black hole and the supermassive black hole. < p > < p > according to stellar evolutionary physics, photons and gases in a star’s nucleus generate an outward pressure, which balances the gravity that drives the transverse matter inward, thus maintaining a stable state, such as the sun. When heavy element atoms (such as iron) in a star fuse, it will not be able to generate pressure that can support the outer layer. When the external pressure is less than the gravity, the star will collapse under the action of its own weight, and the core collapse supernova explosion will occur, thus forming a black hole. < / P > < p > this process can explain how a star 130 times the mass of the sun can form a black hole up to 65 times the mass of the sun. But for heavier stars, the phenomenon of pair instability is also a factor to be considered. When photons in a star’s nucleus are extremely energetic, they form electron and anti electron pairs. These positive and negative electron pairs produce less pressure than photons, making stars more unstable and prone to gravitational collapse, leading to violent explosions that can destroy everything. Even larger stars, such as 200 times the mass of the sun, eventually collapse into black holes at least 120 times the mass of the sun. Therefore, collapsing stars do not produce black holes with masses between 65 and 120 times the mass of the sun, a range called pair instability mass gap. However, the heaviest of the two black holes that emit gw190521 gravitational wave signals now has a mass of 85 times the mass of the sun, which is the first black hole detected to have a mass in this range. Nelson Christensen, a member of Virgo and a researcher at the French National Center for scientific research (CNRS), said: “the fact that we have observed black holes with masses in this region is enough to make many astrophysicists scratching their ears and trying to study the origin of these black holes.” < / P > < p > one possibility is the hierarchical merger mentioned in the second article: two primitive black holes are merged by two smaller black holes before they are close to each other and merge. < / P > < p > “this astrophysical event raises more questions than it answers,” said Alan Weinstein, a physics professor at Caltech and a member of LIGO. “It’s exciting from the perspective of exploration and physics.” The duration of this signal is very short, less than 0.1 seconds. The researchers speculate that gw190521’s gravitational wave signal came from a galaxy 5 gigaseconds away from earth, reflecting the state of the universe at half its present age, and took seven billion years to reach earth. This is also the most remote source of gravitational waves detected so far. < p > < p > as for the source of the signal, according to the advanced computational modeling tools, scientists speculate that gw190521 is the most likely signal generated by the merger of two black holes with special properties. So far, almost all confirmed gravitational wave signals come from binary star merging, including double black hole merging and double neutron star merging. The LIGO Virgo team also measured the rotation of the two black holes, and found that as the black holes rotated closer to each other, their respective rotation axes might deviate from the axis of their orbits. As the two giants keep spinning close to each other, the misalignment of their axes can cause their orbits to wobble or precession. < / P > < p > this merger produces a black hole with a mass of 142 times that of the sun, which can release 8 times the mass of the sun to the universe in the form of gravitational waves. “It’s different from the chirp like signal we usually detect,” Christensen said Compared with the gravitational wave detected by LIGO for the first time in 2015, “this signal is like a loud noise, which is the most powerful signal source found by LIGO and Virgo so far.” The LIGO project, funded by the National Science Foundation (NSF), consists of a pair of 4 km long interferometers. “LIGO once again surprised us. It’s not just because it detects black holes of inexplicable size, but because the technology it uses is not specifically designed to study galaxy mergers, “says Pedro marronetti, NSF’s director of the gravitational physics program.” it shows us that the instrument has the ability to detect signals from unforeseen astrophysical events. LIGO tells us that it can observe unexpected phenomena. ” < / P > < p > when LIGO and Virgo detectors detect gravitational wave signals passing through the earth, the automatic search program combs the input data to find signals of interest to researchers. There are two search methods: one is to search for data patterns that may be generated by a system composed of two dense stars; the other is more general “burst searches” to find all abnormal signals. Salvatore Vitale, a member of LIGO and an assistant professor of physics at MIT, likens the algorithm of finding a specific pattern to “crossing data with a comb, and always catching something of a certain shape”, while burst search is a more general method. < p > < p > in the discovery of gw190521 signal, it is the second method that selects the clearer signal. It is found that the possibility of this gravitational wave coming from other sources other than binary star merging is very small. < / P > < p > “the threshold for us to discover something new is very high,” Weinstein said. “We always follow the Okam razor principle: the simpler the explanation, the better. In terms of gw190521 signal, the best explanation is double black holes (merger).” < / P > < p > but what if this gravitational wave signal came from a completely new celestial body? This is a fascinating prospect, and in the published paper, scientists also briefly considered other possible sources of gravitational waves. For example, it could have been emitted by a collapsing star in the Milky way, or a string from the early universe. However, these hypotheses are not as good as the double black hole merging hypothesis. < / P > < p > “since LIGO was put into use, all observations with high reliability have been collisions of black holes or neutron stars.” Weinstein also said, “in this phenomenon, our analysis shows that it may not have been such a collision. Although this phenomenon is consistent with the merging event of double black holes with unique mass, other explanations are not optimistic, it still enhances our confidence. It’s an exciting thing. Because we all look forward to finding new things, eager to find unexpected phenomena to challenge our existing knowledge. And this astronomical discovery has done that. ” The release and download schedule of Microsoft Flight Simulation varies from region to region