What is the mysterious cosmic "black hole"?

Decades ago, scientists predicted this celestial body called "black hole" according to the theoretical research of Einstein's general relativity.

A black hole is a very strange celestial body. Its volume is small, but its density is extremely high, with tens of tons or even higher per cubic centimeter. If you take out a piece of matter the size of a grain of rice from a black hole, you have to use tens of thousands of tons of boats to tow it. If the sun becomes a black hole, its radius will have to be reduced to less than 3 kilometers.

Because of the high density of a black hole, its gravity is particularly strong. As we all know, due to the gravity of the earth, the kicked football will still fall to the earth. And high-speed satellites can overcome the gravity of the earth and fly to space to travel. The situation of black holes is different from that of the earth. The gravity of a black hole is extremely strong, and all substances inside the black hole, including the fastest light, cannot escape the huge gravity of the black hole. Not only that, it can also attract light and other substances around it. A black hole is like a bottomless pit. When anything reaches it, there is no need to "crawl" out again. It is very vivid to name them "black holes".

It is speculated that a "black hole" is the destination of the collapse of an old star whose mass is more than three times that of the sun. A star with a mass more than three times that of the sun will collapse into a black hole when its nuclear fuel is exhausted. If the star mass does not exceed 1~2 solar masses, it will collapse into a white dwarf. If the star mass is in the range of 1~3 solar mass, it will collapse into a neutron star.

Black hole jet impact phenomenon

Since black holes are invisible, how can we find them? This must take advantage of the huge gravity of black holes. If a black hole is a member of a binary star system and the other member is an observable star, then the motion of the star will change regularly due to the gravity of the black hole, and the existence of an invisible black hole can be detected from this change. In addition, the matter around the black hole will be shown in a strange way under the attraction of the strong gravity of the black hole. When they continue to flow into black holes, they will emit strong X-rays and γ-rays, which is another clue to find black holes at present. In addition, black holes will also affect the propagation of neighboring light, resulting in the so-called gravitational lens phenomenon. Of course, all these tasks of finding black holes are not easy.

"Swan X- 1" is a strong K ray source. It has an invisible companion star. According to the motion of "Swan X- 1", it can be judged that the companion star's mass is about 10 times that of the sun. Many people think it may be a stellar black hole. Astronomers also found that the cores of many galaxies have violent activities, which we call active galactic nuclei. Their center is probably a giant black hole, greedily devouring the surrounding matter and releasing huge energy. Some people think that there is a big black hole in the center of our galaxy, which is millions of times the mass of the sun. Learning point

neutron star

Simply put, a neutron star is a kind of star between a star and a black hole, which is formed by the collapse of a star with insufficient mass to form a black hole at the end of its life. Neutron stars have extremely high density and mass, and their density is many times greater than that of any matter on earth. According to calculations, when the mass of an elderly star is greater than that of ten suns, it may eventually become a neutron star, while a star with a mass less than ten suns can only become a white dwarf.