Black holes are such an objects in space whose gravity is so powerful that even light cannot escape from it. According to the theory of general relativity, mass causes curvature in space and time. The greater the mass, the greater the velocity.
A black hole is the gravitational field that remains when a star collapses under its own gravity to an infinitesimal point. Within a certain distance from the point—at the black hole’s event horizon—gravity grows so strong that not even light can escape. This radius of critical value is called the Schwarzschild Radius. This radius varies for different bodies and depends on the mass of that body. This radius is 3 km for the mass of the Sun, if we cover the Sun in a radius of 3 km, it will become a black hole. For the Earth it is only 9mm.
Classification of black holes
Roughly black holes are placed in three main categories. They are:
- Micro black holes
- Stellar mass black holes
- Super massive black holes
Now let's discuss these three one by one.
Micro Black Holes
They are also called quantum mechanical black holes, they are hypothetical black holes, that is, there is no evidence of their presence so far. The concept of black holes with mass less than stellar mass was given by Stephen Hawking in 1971. There is a limit to the mass of these microscopic black holes. According to the theories of the Schwarzschild radius and the Compton wavelength, the minimum mass of a black hole can be 22 micro grams, which is called Planck mass.
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According to Quantum mechanics, Black holes may have played an important role in the atmosphere of extreme energy and density at the beginning of the universe. But such black holes were unstable and would have disappeared by Hawking radiation. In a research paper in Stephen Hawking in 1975, it was shown that the smaller the black hole under the influence of the quantum mechanics effect, the faster it will dissipate. As a result, new particles may have suddenly been bombarded by black hole explosions.
According to mathematical calculations, the energy required to create a microscopic black hole should be 1019 GeV. This is more than the energy that can be generated by the technology available in the present.
Stellar Mass Black Holes
The second class of black holes consists of black holes of stellar mass. Most research has been done on these black holes. They are found in nature, unlike the subtle black hole. The process of making them is also known to scientists. According to the name, these black holes are formed due to the collapse / contraction during the death of a superstar. The nucleus of these giant stars has the capability of fusion of heavy elements on a full scale. And these stars combine elements such as carbon, neon, oxygen, silicon, sulfur.
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As the fusion reaches the nickel-56 via the alpha ladder, the reaction chain stops. Fusion of zinc with nickel is not thermally conducive, causing the nucleus to stop reacting, leaving the nucleus inactive. In this case, the star starts to shrink with its own gravity. If the mass of the star is high then no one can stop its contraction and it collapses into a black hole.
The critical boundary of a black hole beyond which nothing can escape, not even light, is called an event horizon. Everything is normal in the context of matter falling into the black hole. But in the context of external inspector, he will find everything different from gravitational time dilation.
As the gravitational pull increases, the red deviation in the light emanating from the material falling in the black hole will increase and as soon as it reaches the event horizon, the excess red deviation will fade. Therefore an external observer would never see the creation of the event horizon of a black hole.
Super massive Black Holes
As the name suggests, these black holes are massive and are found in the center of galaxies. They have millions times more mass than the Sun. But the density of these black holes may be less than the density of water. The reason is simple that the Schwarzschild radius is proportional to its mass and the volume is proportional to the cube of the radius. The density of a black hole is inversely proportional to the square of mass in it. The larger the mass of a black hole, the lower its density.
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In addition, the tidal force of these black holes is also very low. The tidal force on the incident horizon of a black hole is inversely proportional to the square of its mass. In this way one will feel the same tidal force between the head and foot of the person standing on the surface of the Earth as between the head and foot of a person standing on the incident horizon of a black hole with a mass of 10 million M*(mass of the Sun).
The process of manufacturing such a strange body is unknown and is a subject of research in the field of astronomy. There are many concepts in this regard. According to one concept, the seeds of these black holes are those black holes with a mass of ten or a few hundred solar masses formed by the death of the superstars and the surrounding stars have been stretched by stretching material from the gas bar.
Some scientists believe that a black hole with an initial stellar mass formed after the death of the initial stars of the universe has become a super massive black hole. The correct concept and theory has not been revealed so far.