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Xinfan Technology News, on August 27, Beijing ti, reported that among all astronomical concepts, black holes might be the most peculiar. The density of black holes is extrely high, even light cannot escape, like a terrifying giant dark trap. As common laws of physics don't apply in black holes, black holes seem as if they were born for science fiction. However, various direct and indirect evidence indicate that black holes indeed exist in the universe.
Einstein's Prophecy
Black holes are an inevitable result of Einstein's general relativity.
German astronor Karl Schwarzschild first predicted the existence of black holes in 1916, considering it to be an inevitable result of Einstein's general relativity. In other words, if Einstein's theory is correct (and all evidence points to this), then black holes must exist. The research of Roger Penrose and Stephen Hawking further solidified the theoretical foundation for the existence of black holes. Their research showed that any star collapsing into a black hole will form a singularity, and traditional physical laws completely fail at this point.
Gamma-ray Bursts
Terrestrial observation equipnt has already detected so gamma-ray bursts produced in the process of black hole formation.
In the 1930s, Indian astrophysicist Subrahmanyan Chandrasekhar conducted research on the fate of stellar nuclear fuel depletion, discovering that the final outco depends on the star's mass. If a star is very massive, say 20 tis the mass of the Sun, its dense core (whose mass alone may reach two or three tis the Sun's mass) will continue to collapse until it forms a black hole. The core's collapse speed is extrely fast, lasting only a few seconds, releasing an astonishing amount of energy in the form of a gamma-ray burst, equivalent to the total energy a normal star emits throughout its lifeti. Terrestrial telescopes have detected multiple gamma-ray bursts, so of which were emitted by galaxies billions of light years away, indicating that indeed we have observed the process of black hole formation.
Gravitational Waves
Pictured is an artist's impression of gravitational wave ripples. The gravitational interaction between two black holes creates ripples in ti, spreading outward in the form of gravitational waves.
Black holes are not always solitary; sotis they appear in pairs, orbiting each other. The gravitational interaction between two black holes creates ripples in ti, spreading outward in the form of gravitational waves, which is another one of the predictions of Einstein's relativity. With the help of observatories like LIGO and Virgo, we now have the ability to detect gravitational waves. In 2016, scientists announced for the first ti the discovery of gravitational waves produced by the rger of two black holes. Since then, more gravitational wave events have been detected. As the sensitivity of the detectors continues to improve, scientists have also detected gravitational waves from events other than black hole rgers, such as black holes colliding with neutron stars and so on.
Invisible Companion
Pictured is an imagined depiction of the orbital motion in the trinary system HR6819.
The events capable of producing gamma-ray bursts or gravitational waves occur in a short ti and can be detected from halfway across the universe. However, considering their nature, most black holes are undetectable. Black holes do not emit any light or radiation, thus they can silently lurk in the darkness, without astronors noticing their existence. However, there is a thod to detect their presence: using the gravitational influence a black hole exerts on other stars. In 2020, while observing the seemingly ordinary stellar system HR6819, astronors noticed unusual movents in the trajectories of two stars, which could only be explained by the presence of a completely invisible object in the system. Calculating its mass, researchers realized there was only one possibility: this object must be a black hole. It is only a thousand light years away from Earth, located in the Milky Way Galaxy, and is the closest black hole discovered to Earth so far.
X-ray
The black hole Cygnus X-1 is currently consuming its giant blue supergiant companion star.
In 1971, while studying a stellar system in the Milky Way Galaxy nad Cygnus X-1, scientists first observed evidence of a black hole's existence. The X-rays generated by this system are extrely bright, but these rays do not co from the black hole or its visible companion star; they are produced by the accretion disk ford as the black hole consus stellar material. As in the case of the HR6819 system ntioned earlier, astronors can also use the orbital trajectory of the visible star to estimate the mass of the invisible object in the Cygnus X-1 system. The final calculation result is approximately 21 tis the mass of the Sun, and considering the relatively small space it occupies, it can only be a black hole, without the need to consider other possibilities.
Supermassive Black Holes
There's also a supermassive black hole at the center of the Milky Way Galaxy.
Besides black holes ford by stellar collapse, there is evidence that supermassive black holes, with masses reaching millions or even billions of tis that of the Sun, might be lurking at the centers of galaxies and may have existed since the early universe. In the so-called "active galaxies," the evidence for the existence of these supermassive black holes is astounding. NASA indicates that around the black holes at the centers of such galaxies are accretion disks that emit extrely intense radiation across various spectral bands. There is a black hole at the center of the Milky Way Galaxy because we have observed that the star rotation speed in that region is alarmingly high, reaching 8% of the speed of light, indicating they must be orbiting around a massively dense but extrely small-object. Current estimates suggest that the black hole at the center of the Milky Way Galaxy has a mass approximately 4 million tis that of the Sun.
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