novelraw Chapter 593 1/5]
Chapter 593 1/5]
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Sina Tech News, Beijing time on August 27, among all astronomical concepts, black holes might be the most bizarre. The density of a black hole is extremely high, so even light cannot escape, resembling a dark and terrifying giant beast. Since the usual physical laws do not apply in black holes, they seem to be made especially for science fiction novels. However, a multitude of direct and indirect evidence indicates that black holes truly do exist in the universe.
Einstein's Prophecy
Black holes are the inevitable result of Einstein's general relativity.
German astronomer Karl Schwarzschild first predicted the existence of black holes in 1916, considering it 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. Roger Penrose and Stephen Hawking's research further solidified the theoretical foundation for the existence of black holes. Their research shows that when any celestial body collapses into a black hole, a singularity will form, and traditional physical laws all fail at this point.
Gamma-ray Bursts
Observation equipment on Earth has detected some gamma-ray bursts that are produced during the formation of black holes.
In the 1930s, Indian astrophysicist Subrahmanyan Chandrasekhar conducted research on the fate of stars after their nuclear fuel is exhausted. He found that the final outcome depends on the mass of the star. If a star is very large, say about 20 times the mass of the Sun, its dense core (whose mass alone can be 2 or 3 times that of the Sun) will continue to collapse inward until it becomes a black hole. The collapse speed of a star's core is extremely fast, taking only a few seconds and releasing an astonishing amount of energy in the form of gamma-ray bursts, equivalent to the total energy released by an ordinary star over its long lifespan. Telescopes on Earth have detected multiple gamma-ray bursts, some from galaxies billions of light-years away, indicating that we have indeed observed the process of black hole birth.
Gravitational Waves
Pictured is an artist's concept of gravitational waves. The gravitational interaction between two black holes forms ripples in spacetime, spreading outward in the form of gravitational waves.
Black holes are not always solitary; sometimes they appear in pairs, orbiting each other. The gravitational interaction between two black holes forms ripples in spacetime, spreading outward in the form of gravitational waves, which is one of the predictions proposed by Einstein's theory of relativity. With the help of observatories like LIGO and Virgo, we now have the capability to detect gravitational waves. In 2016, scientists announced for the first time the discovery of gravitational waves produced by the merger of two black holes. Since then, we have detected multiple gravitational wave events. As detector sensitivity continues to improve, scientists have also detected gravitational waves produced by events other than black hole mergers, such as black hole and neutron star collisions.
Invisible Companion Star
Pictured is the conceptual orbital illustration of several celestial bodies within the HR 6819 triple star system.
Gamma-ray bursts or gravitational waves are all high-energy events that occur in a short period of time, perhaps visible from half a universe away. But due to their nature, most black holes are undetectable. Black holes do not emit any light or radiation, so they can quietly lurk in space without astronomers realizing their presence. However, there is a way to detect their presence: by using the gravitational effects black holes have on other stars. In 2020, astronomers observed the seemingly ordinary binary star system HR 6819 and found peculiarities in the motion paths of the two stars. It could only be explained by an entirely invisible celestial body within the system. After calculating its mass, researchers realized there could only be one truth: this celestial body must be a black hole. It is only a thousand light-years from Earth, located within the Milky Way Galaxy, making it the closest black hole to Earth discovered so far.
X-rays
Black hole Cygnus X-1 is consuming a nearby large blue companion star.
In 1971, scientists first observed evidence of a black hole while studying a binary star system in the Milky Way Galaxy named Cygnus X-1. The X-rays produced by this system are extremely bright, but they do not come from the black hole or its visible companion star. They are produced by an accretion disk formed as the black hole absorbs star material. Just like the mentioned binary star system HR 6819, astronomers can also estimate the mass of the invisible celestial body in the Cygnus X-1 system using the motion paths of the visible star. The final calculation results were about 21 times the mass of the Sun. Considering the small space occupied by this celestial body, it indicates that it can only be a black hole without considering other possibilities.