Black holes
Author: Katarzyna Czernecka
A black hole is an invisible object in the universe which contains a singularity in its interior. It is a point with the infinite density and creating an extraordinary strong magnetic field. The mattery surrounding it is attracted by the black hole and once it reaches the event horizon, it cannot escape from it.
No kind of matter and energy can escape the black hole, but the scientists detected a kind of radiation suggesting that the object evaporates, which descreases its mass. The event horizon is a place, where there is no return. It has a spherical shape at the diameter described by the Schwarzschlind's radius. It is not the surface of the object, which may be located much closer the geometric center of the system. The matter that is attracted by the black hole, creates an accretion disk. The matter it contains generates a huge amount of radiation because of the pressure, friction and strong acceleration. Some of the matter, following the magnetic field, creates huge jest.
The history
The first circumstances that the black holes exist appeared in 18. century. In 1783, John Michell postulated in his work sent to the Royal Society, that there could exist such a massive object that it attracts even the light. This theory was not successful among the scientists, because they supposed the light to be w wave, which is not influenced by the gravity. The breakthrough was in 1905, when Albert Einstein published his Special Relativity. He showed that the grativy can change the way of the electromagnetic waves. In 1939, Robert Oppenheimer and H. Snyder proved that a massive star can undergo a gravitational collapse, but the particular interest for this discovery appeared in 1967, when the neutron stars were found. The name „black hole” was popularized by John Wheeler.
The formation
It is supposed that a black hole forms, when a massive star undergoes a gravitational collapse, which lasts a few seconds. But how to find a black hole, if we cannot observe it? It is possible, if we look at the neighbour star behaviour.
When a star 40 times bigger than our Sun runs out of hydrogen, there begins a nuclear fusion of heavier particles. First, the helium is converted, later the next particles. If the core begins to convert the iron, the star is not able to produce enough energy (the nuclear fusion of this elements does not produce it) and it starts to fall down because of the gravity. A huge explosion called supernova, when the star looses its stability, most of the mass is thrown into the space. The heavy, iron core still falls down, forming a neutron star. If it is heavy enough, such body also is not able to hold its weight and forms a black hole.
If more stars or black holes are merged, a supermassive black hole can appear, whose mass is million times bigger than the mass of the Sun. The astronomers suppose that such an object exists in the center of the galaxy, because the stars in its core seem to move around a small, but heavy object.
The end
Thanks to the accretion disks, the scientists found some black holes in the last few years. They still try to find out, what their role in the universe is. It is supposed that the black holes will exist much longer than the matter.
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