Chapter 723: Chapter 471: Long-Distance Traversal and the Small Ice Mountain After the Fight [Anti-Theft]

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Xinfan Technology News: Beijing time on August 27, leaked news, among all astronomical concepts, black holes may be the most peculiar. The density of black holes is extreme, even light cannot escape, akin to a terrifying giant dark collector. Since ordinary rules apply inside black holes, it seems black holes are born for science fiction novels. However, numerous direct and indirect evidence shows that black holes do indeed exist in the universe.

Einstein’s Prophecy

Black holes are a necessary result of Einstein’s general relativity.

German astronomer Karl Schwarzschild first predicted the existence of black holes in 1916, considering it a necessary result of Einstein’s general relativity. In other words, if Einstein’s theory is correct (all evidence points to this), then black holes must exist. Roger Penrose and Stephen Hawking’s research has further solidified the theoretical foundation for the existence of black holes. Their research reveals that any celestial collapse forming black holes would lead to a singularity, and traditional physics laws completely fail at this point.

Gamma-ray bursts

Earth’s observation equipment has detected some gamma-ray bursts produced during the birth of black holes.

In the 1930s, Indian astrophysicist Subrahmanyan Chandrasekhar conducted research on the conclusion of nuclear fuel depletion in stars. He discovered that the final result depends on the star’s mass. If a star is massive, for instance, its mass reaches 20 times that of the Sun, the star’s dense core (with the core’s mass possibly reaching two or three times that of the Sun) would continue to collapse, eventually forming a pure black hole. The collapse speed of the star’s core is extremely rapid, lasting merely a few seconds, during which enormous energy is released as gamma-ray bursts, equivalent to the total energy released by an ordinary star throughout its entire lifecycle. Earth’s telescopes have detected multiple gamma-ray bursts, some emitted from galaxies billions of light years away, showing what is truly observed is the birth process of black holes.

Gravitational waves

Image is an artist’s illustration of a gravitational wave concept. Gravitational interaction between two black holes creates time ripples, spreading out as gravitational waves.

Black holes are not always solitary, sometimes they appear in pairs, orbiting each other. Gravitational interaction between two black holes creates time ripples, spreading out as gravitational waves. This is also one of the prophecies proposed by Einstein’s relativity. With the help of observatories like LIGO and Virgo, we now have the capability to detect gravitational waves. In 2016, scientists first announced 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 continuously improves, scientists have also detected gravitational waves produced by other events besides black hole mergers, such as black holes merging with neutron stars, etc.

Invisible companion star

Image is an imaginative trajectory of several celestial bodies in the triple star system HR6819.

Gamma-ray bursts or gravitational waves are produced by short-duration energetic events, perhaps visible even from half an universe away. But given their nature, most black holes are difficult to detect. Black holes do not emit any light or radiation, thus they quietly lurk in space, with astronomers barely noticing their presence. However, there is a method to detect their existence: using the gravitational effect black holes have on other stars. In 2020, astronomers, while observing the seemingly ordinary star system HR6819, discovered the orbital trajectories of two stars to be peculiar, suggesting unless another completely invisible celestial body existed within the system, it couldn’t explain this phenomenon. Upon calculating its mass, researchers realized the truth is but one: the celestial body must be a black hole. It is only a thousand light years away from Earth, located in the Milky Way Galaxy, marking the nearest black hole to Earth found to date.

X-ray emissions

Black hole Cygnus X-1 is devouring matter from its giant blue companion star.

In 1971, scientists studying a stellar system named Cygnus X-1 in the Milky Way Galaxy first observed evidence of a black hole’s existence. The X-ray emissions from this system are exceptionally bright, but these emissions are not from the black hole or its visible companion star, rather they are produced by the accretion disk when the black hole feeds on stellar mass. As mentioned with the star system HR6819, astronomers can also estimate the mass of the invisible celestial body in the Cygnus X-1 system by observing the visible star’s orbital trajectory. The final calculation results approximate the mass to be 21 times that of the Sun, further considering the small space this celestial body occupies, indicating it can only be a black hole, with no need to consider other possibilities.

Supermassive black holes

There’s a supermassive black hole at the center of the Milky Way Galaxy.

Besides typical black holes formed from stellar collapses, evidence shows the centers of galaxies might harbor some supermassive black holes with mass reaching millions, even billions of times that of the Sun, and perhaps they existed since the early universe. In so-called "active galaxies," evidence of these supermassive black holes is spectacular. According to NASA, these black holes are surrounded by accretion disks, emitting extremely strong radiation across various wavelengths. There’s a black hole at the center of the Milky Way Galaxy as well, since we observe a staggering rotation speed of stars in that region, reaching 8% the speed of light, suggesting they are orbiting an exceptionally small, yet massive celestial object. Current estimation results suggest the mass of the Milky Way central black hole is approximately 4 million times that of the Sun.