# Black holes

Today, at least, heard or read about black holes. But there was a time when that name was neither scientific nor popular literature.

Black holes - this is causing huge gravitational forces. They occur when a strong contraction in the course of a large mass of material increasing its gravitational field becomes so strong that not even light produces. Faster than light in nature, nothing can not move, it means that black holes do not emit anything. The black holes can only fall under the influence of the enormous gravity forces, but there is no way out. There are many books about the properties of gravity is very strongly compressed spherical mass. Solutions of Einstein's equations for this case was found K. Schwarzschild and therefore is called the Schwarzschild gravitational field. When you compress the masses to smaller and smaller radius, gradually manifest deviations from Newton's law - the attractive force was obtained even if only slightly, but somewhat larger. But most interesting is that there is a certain range, to which the compressive force of gravity tends to infinity for each mass. This range has been called the gravitational radius. The gravitational radius of the greater, the larger the mass of the body. For example, for the mass of the Earth is just one centimeter, three kilometers to the Sun's mass.

The question arises: what would happen if the mass will have a radius of less gravity? This question gave the answer even in the 20th Art. American physicist Robert Oppenheimer and H. Snyder. If a spherical mass, decreasing to shrink to a size equal to or less than the gravitational radius, it then no internal pressure of the substance, no external forces will not be able to stop the further compression. But with the rapid compression - matter falls to the center - the gravitational force is not felt.

Everyone knows that the free fall comes a state of weightlessness and any body, not meeting support, lose weight. The same happens with the shrinking mass: on the surface of the force of gravity - gravity - is not felt. can not stop the mass compression After reaching the gravitational radius sizes. She strives irresistibly to the center. Such a process physicists call gravitational collapse - so there are black holes. It is inside a sphere with a radius equal to gravity, gravity is so strong that not even light produces. This area J. Wheeler called in 1968 by the black hole.

The name proved to be successful, and it was immediately picked up by all the experts. The boundary of a black hole is called the event horizon. The name of this is understandable, because out of that border do not go to the outside observer, no signals that could provide information about the events taking place inside. About what happens inside a black hole, an external observer will never know anything.

But how can you create a black hole? At first glance, this task is simple. It is necessary to take some weight and shrink it to the size of the gravitational radius. This is certainly true. However, it is extremely complicated by the fact that the value of the gravitational radius is very small, even for large masses. So if you take the weight of a small mountain, it would have to be compressed to the size of an atomic nucleus! Of course, can not be considered to create an artificial black hole in modern laboratories. But it appears that nature itself has created a black hole, however, a sufficiently large mass. Such black holes can occur at the end of life sufficiently massive star. If the star at the end of the active evolution has a lot of, let's say, ten solar masses or more, it is very likely that the force of their own gravity to compress its gravitational radius sizes and turn into a black hole. Finally, it is likely that the supermassive black hole with a mass of one hundred thousand to a billion solar masses or more occur in the centers of giant galaxies, star systems.