A black hole is a neutron star, or more precisely, a black hole is one of the varieties of neutron stars.

A black hole, like a neutron star, consists of neutrons. Moreover, this is not a neutron gas, in which neutrons are in a free state, but a very dense substance with the density of an atomic nucleus.

Black holes and neutron stars form as a result of gravitational collapse, when the gas pressure in the star cannot balance its gravitational compression. This compresses the star to a very small size and very high density, so that electrons are squeezed into protons and neutrons are formed.

Note that the average lifetime of a free neutron is about 15 minutes (half-life is about 10 minutes). Therefore, neutrons in neutron stars and black holes can only be in a bound state, as in atomic nuclei. Therefore, a neutron star and a black hole are like an atomic nucleus of macroscopic size, in which there are no protons.

The absence of protons is one difference between a black hole and a neutron star from an atomic nucleus. The second difference is due to the fact that in ordinary atomic nuclei neutrons and protons are “glued” to each other using nuclear forces (the so-called “strong” interaction). And in neutron stars, neutrons are “glued together” by gravity.

The fact is that nuclear forces also need protons to “glue” neutrons together. There are no nuclei that consist only of neutrons. There must be at least one proton. And for gravity, no protons are needed to “glue” neutrons together.

Another difference between gravity and nuclear forces is that gravity is a long-range interaction, and nuclear forces are a short-range interaction. Therefore, atomic nuclei cannot be macroscopic in size. Starting with uranium, all elements on the periodic table have unstable nuclei that decay because positively charged protons repel each other and break apart large nuclei.

Neutron stars and black holes do not have this problem, since, firstly, gravitational forces are long-range, and, secondly, there are no positively charged protons in neutron stars and black holes.

A neutron star and a black hole under the influence of gravitational forces have the shape of a ball, or rather an ellipsoid of rotation, since all neutron stars (and black holes) rotate around their axis. And quite quickly, with rotation periods of several seconds or less.

The fact is that neutron stars and black holes are formed from ordinary stars by their strong compression under the influence of gravity. Therefore, according to the law of conservation of torque, they must rotate very quickly.

Are the surfaces of black holes and neutron stars solid? Not in the sense of a solid body, as an aggregate state of matter, but in the sense of a clear surface of a ball, without a neutron atmosphere. Apparently, yes, black holes and neutron stars have a solid surface. The neutron atmosphere and neutron liquid are neutrons in a free state, which means they must decay.

But this does not mean that if we, for example, drop some “product” made of neutrons with the density of an atomic nucleus onto the surface of a black hole or a neutron star, then it will remain on the surface of the star. Such a hypothetical “product” will immediately be “sucked” into the interior of a neutron star and a black hole.

The difference between black holes and neutron stars

The gravity of a black hole is such that the escape velocity on its surface exceeds the speed of light. Therefore, light from the surface of a black hole cannot escape into outer space forever. Gravitational forces bend the light beam back.

If there is a light source on the surface of a black hole, then the photons of this light first fly upward, and then turn and fall back to the surface of the black hole. Or these photons begin to rotate around the black hole in an elliptical orbit. The latter occurs on a black hole on the surface of which the first escape velocity is less than the speed of light. In this case, the photon can escape from the surface of the black hole, but it becomes a permanent companion of the black hole.

And on the surface of all other neutron stars that are not black holes, the second escape velocity is less than the speed of light. Therefore, if there is a light source on the surface of such a neutron hole, then photons from this light source leave the surface of such a neutron star in hyperbolic orbits.

It is clear that all these considerations apply not only to visible light, but also to any electromagnetic radiation. That is, not only visible light, but also radio waves, infrared rays, ultraviolet, x-rays and gamma radiation cannot leave a black hole. The maximum that photons of these radiations and waves can do is begin to rotate around a black hole if for a given black hole the speed of light is greater than the first cosmic speed on the surface of the star.

That is why such neutron stars are called “black holes”. Nothing flies out of a black hole, but anything can fly in. (We will not consider the evaporation of black holes due to quantum tunneling here.)

That is, it is clear that there is actually no hole in space there. Just like there is no hole in space at the location of an ordinary neutron star or at the location of an ordinary star.

Holes in space exist only in books by science fiction writers, popular science publications and television programs. Publications and television programs need to financially recoup the costs of circulation and ratings. Therefore, they have to emotionally amaze their readers and television viewers with facts that cannot be verified at the current level of development of science and technology, but which may appear in some mathematical models. (The lay public usually does not suspect that mathematical models in physics are always secondary, that physics is an experimental science, and that mathematical models of physical objects tend to change in the future as new experimental data become available.)

If we could stand on the surface of a black hole, then looking up we would see a translucent mirror instead of a starry sky. That is, we would see there both the surrounding space (since the black hole receives all the radiation sent to it) and the light that returns to us without being able to overcome gravity. This return of light back has a mirror effect.

Exactly the same translucent “mirror” on the surface of a black hole occurs for other types of electromagnetic radiation (radio waves, X-rays, ultraviolet, etc.)

This post is a summary for the fifth lesson in the astrophysics course program for high school. It contains a description of supernova explosions, processes of formation of neutron stars (pulsars) and stellar-mass black holes, both single and in stellar pairs. And a few words about brown dwarfs.

First, I will repeat the picture showing the classification of types of stars and their evolution depending on their masses:

1. Outbursts of novae and supernovae.
The burning of helium in the depths of stars ends with the formation of red giants and their outbursts as new with education white dwarfs or the formation of red supergiants and their outbursts as supernovae with education neutron stars or black holes, as well as nebulae from the shells ejected by these stars. Often the masses of the ejected shells exceed the masses of the “mummies” of these stars - neutron stars and black holes. To understand the scale of this phenomenon, I will provide a video of the supernova 2015F explosion at a distance of 50 million light years from us. years of galaxy NGC 2442:

Another example is the supernova of 1054 in our Galaxy, as a result of which the Crab Nebula and a neutron star were formed at a distance of 6.5 thousand light years from us. years. In this case, the mass of the resulting neutron star is ~ 2 solar masses, and the mass of the ejected shell is ~ 5 solar masses. Contemporaries estimated the brightness of this supernova to be about 4-5 times greater than that of Venus. If such a supernova erupted a thousand times closer (6.5 light years), then it would sparkle in our sky 4000 times brighter than the Moon, but a hundred times fainter than the Sun.

2. Neutron stars.
Stars of large masses (classes O, B, A) after hydrogen burns out into helium and during the process of helium burnout predominantly into carbon, oxygen and nitrogen enter a fairly short stage red supergiant and upon completion of the helium-carbon cycle, they also shed the shell and flare up as "Supernovae". Their depths are also compressed under the influence of gravity. But the pressure of the degenerate electron gas can no longer, like in white dwarfs, stop this gravitational self-compression. Therefore, the temperature in the bowels of these stars rises and thermonuclear reactions begin to occur in them, as a result of which the following elements of the periodic table are formed. Up to gland.

Why before iron? Because the formation of nuclei with a high atomic number does not involve the release of energy, but the absorption of it. But taking it from other nuclei is not so easy. Of course, elements with high atomic numbers are formed in the interiors of these stars. But in much smaller quantities than iron.

But then evolution splits. Not too massive stars (classes A and partially IN) turn into neutron stars. In which electrons are literally imprinted into protons and most of the star’s body turns into a huge neutron core. Consisting of ordinary neutrons touching and even pressed into each other. The density of the substance is on the order of several billion tons per cubic centimeter. A typical neutron star diameter- about 10-20 kilometers. A neutron star is the second stable type of "mummy" of a dead star. Their masses typically range from about 1.3 to 2.1 solar masses (according to observational data).

Single neutron stars are almost impossible to see optically due to their extremely low luminosity. But some of them find themselves as pulsars. What it is? Almost all stars rotate around their axis and have a fairly strong magnetic field. For example, our Sun rotates around its axis in about a month.

Now imagine that its diameter will decrease a hundred thousand times. It is clear that, thanks to the law of conservation of angular momentum, it will rotate much faster. And the magnetic field of such a star near its surface will be many orders of magnitude stronger than the solar one. Most neutron stars have a rotation period around their axis of tenths to hundredths of a second. It is known from observations that the fastest rotating pulsar makes just over 700 revolutions around its axis per second, and the slowest rotating one makes one revolution in more than 23 seconds.

Now imagine that such a star’s magnetic axis, like the Earth’s, does not coincide with the axis of rotation. Hard radiation from such a star will be concentrated in narrow cones along the magnetic axis. And if this cone “touches” the Earth with the rotation period of the star, then we will see this star as a pulsating source of radiation. Like a flashlight rotated by our hand.

Such a pulsar (neutron star) was formed after a supernova explosion in 1054, which occurred just during the visit of Cardinal Humbert to Constantinople. As a result of which there was a final break between the Catholic and Orthodox churches. This pulsar itself makes 30 revolutions per second. And the shell it ejected with a mass of ~ 5 solar masses looks like Crab Nebula:

3. Black holes (stellar masses).
Finally, fairly massive stars (classes ABOUT and partially IN) end their life journey with the third type of “mummy” - black hole. Such an object arises when the mass of a stellar remnant is so large that the pressure of contacting neutrons (the pressure of a degenerate neutron gas) in the depths of this remnant cannot resist its gravitational self-compression. Observations show that the mass boundary between neutron stars and black holes lies in the vicinity of ~2.1 solar masses.

It is impossible to observe a single black hole directly. For no particle can escape from its surface (if it exists). Even a particle of light is a photon.

4. Neutron stars and black holes in binary star systems.
Single neutron stars and stellar-mass black holes are practically unobservable. But in cases where they are one of two or more stars in close star systems, such observations become possible. Because with their gravity they can “suck out” the outer shells of their neighbors, which still remain normal stars.

With this "suction" around a neutron star or black hole, a accretion disk, the matter of which partially “slides” towards a neutron star or black hole and is partially thrown away from it in two jets. This process can be recorded. An example is the binary star system in SS433, one component of which is either a neutron star or a black hole. And the second one is still an ordinary star:

5. Brown dwarfs.
Stars with masses noticeably less than the solar mass and up to ~0.08 solar masses are class M red dwarfs. They will operate on the hydrogen-helium cycle for a time greater than the age of the Universe. In objects with masses less than this limit, for a number of reasons, a stationary long-running thermonuclear fusion is not possible. Such stars are called brown dwarfs. Their surface temperature is so low that they are almost invisible in optics. But they shine in the infrared range. For the combination of these reasons, they are often called substars.

The mass range of brown dwarfs is from 0.012 to 0.08 solar masses. Objects with a mass less than 0.012 solar masses (~ 12 Jupiter masses) can only be planets. Gas giants. Due to slow gravitational self-compression, they radiate noticeably more energy than they receive from their parent stars. Thus, Jupiter, based on the sum of all ranges, emits approximately twice as much energy as it receives from the Sun.

What's happened black hole? Why is it called black? What happens in the stars? How are a neutron star and a black hole related? Is the Large Hadron Collider capable of creating black holes, and what does this mean for us?

What's happened star??? If you don’t know yet, our Sun is also a star. This large object is capable of emitting electromagnetic waves using thermonuclear fusion (this is not the most accurate of definitions). If it is not clear, we can say this: a star is a large spherical object, inside of which, with the help of nuclear reactions, a very, very, very large amount of energy is generated, part of which is used to emit visible light. In addition to ordinary light, heat (infrared radiation), radio waves, ultraviolet, etc. are emitted.

Nuclear reactions occur in any star in the same way as in nuclear power plants, with only two main differences.

1. Nuclear fusion reactions occur in stars, that is, the combination of nuclei, and in nuclear power plants – nuclear decay. In the first case, 3 times more energy is released, thousands of times less cost, since only hydrogen is needed, and it is relatively inexpensive. Also, in the first case there is no harmful waste: only harmless helium is released. Now, of course, you are wondering why such reactions are not used at nuclear power plants? Because it is UNCONTROLLED and easily leads to a nuclear explosion, and this reaction requires a temperature of several million degrees. For humans, nuclear fusion is the most important and most difficult task (no one has yet figured out a way to control thermonuclear fusion), given that our energy sources are running out.

2. In stars, more matter is involved in reactions than in nuclear power plants, and, naturally, there is more energy output there.

Now about the evolution of stars. Every star is born, grows, ages and dies (extinguishes). Based on their evolutionary style, stars are divided into three categories depending on their mass.

First category – stars with a mass less than 1.4 * The mass of the Sun. In such stars, all the “fuel” slowly turns into metal, because due to the synthesis (combination) of nuclei, more and more “multinuclear” (heavy) elements appear, and these are metals. True, the last stage of the evolution of such stars has not been recorded (it is difficult to detect metal balls), this is just a theory.

Second category – stars in mass exceeding the mass of stars of the first category, but less than three solar masses. As a result of evolution, such stars lose the balance of internal forces of attraction and repulsion. As a result, their outer shell is thrown into space, and the inner shell (from the law of conservation of momentum) begins to “furiously” shrink. A neutron star is formed. It consists almost entirely of neutrons, that is, particles that have no electrical charge. The most remarkable thing about a neutron star – this is its density, because to become neutron, a star needs to be compressed into a ball with a diameter of only about 300 km, and this is very small. So its density is very high - about tens of trillions of kg in one cubic meter, which is billions of times greater than the density of the densest substances on Earth. Where did this density come from? The fact is that all substances on Earth consist of atoms, which in turn consist of nuclei. Each atom can be imagined as a large empty ball (absolutely empty), in the center of which there is a small nucleus. The nucleus contains the entire mass of the atom (besides the nucleus, the atom contains only electrons, but their mass is very small). The diameter of the nucleus is 1000 times smaller than an atom. This means that the volume of the nucleus is 1000*1000*1000 = 1 billion times smaller than an atom. And hence the density of the nucleus is billions of times greater than the density of the atom. What happens in a neutron star? Atoms cease to exist as a form of matter; they are replaced by nuclei. That is why the density of such stars is billions of times greater than the density of terrestrial substances.

We all know that heavy objects (planets, stars) strongly attract everything around them. Neutron stars are discovered that way. They greatly bend the orbits of other visible stars nearby.

Third category of stars – stars with a mass greater than three times the mass of the Sun. Such stars, having become neutron, compress further and turn into black holes. Their density is tens of thousands of times greater than the density of neutron stars. Having such a huge density, a black hole acquires the ability of very strong gravity (the ability to attract surrounding bodies). With such gravity, the star does not allow even electromagnetic waves, and therefore light, to leave its limits. That is, a black hole does not emit light. Lack of any light – This is darkness, that's why a black hole is called black. It is always black and cannot be seen with any telescope. Everyone knows that due to their gravity, black holes are capable of sucking in all surrounding bodies in a large volume. This is why people are wary of launching the Large Hadron Collider, in the work of which, according to scientists, the appearance of black microholes is possible. However, these microholes are very different from ordinary ones: they are unstable because their lifetime is very short, and have not been practically proven. Moreover, scientists claim that these microholes have a completely different nature compared to ordinary black holes and are not capable of absorbing matter.

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Calculations show that during a supernova explosion with M ~ 25M, a dense neutron core (neutron star) with a mass of ~ 1.6M remains. In stars with a residual mass M > 1.4M that have not reached the supernova stage, the pressure of the degenerate electron gas is also unable to balance the gravitational forces and the star is compressed to a state of nuclear density. The mechanism of this gravitational collapse is the same as during a supernova explosion. The pressure and temperature inside the star reach such values ​​at which electrons and protons seem to be “pressed” into each other and as a result of the reaction

after the emission of neutrinos, neutrons are formed, occupying a much smaller phase volume than electrons. A so-called neutron star appears, the density of which reaches 10 14 - 10 15 g/cm 3 . The characteristic size of a neutron star is 10 - 15 km. In a sense, a neutron star is a giant atomic nucleus. Further gravitational compression is prevented by the pressure of nuclear matter arising due to the interaction of neutrons. This is also the degeneracy pressure, as previously in the case of a white dwarf, but it is the degeneracy pressure of a much denser neutron gas. This pressure is able to hold masses up to 3.2M.
Neutrinos produced at the moment of collapse cool the neutron star quite quickly. According to theoretical estimates, its temperature drops from 10 11 to 10 9 K in a time of ~ 100 s. Further, the cooling rate decreases slightly. However, it is quite high on an astronomical scale. A decrease in temperature from 10 9 to 10 8 K occurs in 100 years and to 10 6 K in a million years. Detecting neutron stars using optical methods is quite difficult due to their small size and low temperature.
In 1967, at the University of Cambridge, Hewish and Bell discovered cosmic sources of periodic electromagnetic radiation - pulsars. The pulse repetition periods of most pulsars lie in the range from 3.3·10 -2 to 4.3 s. According to modern concepts, pulsars are rotating neutron stars with a mass of 1 - 3M and a diameter of 10 - 20 km. Only compact objects with the properties of neutron stars can maintain their shape without collapsing at such rotational speeds. Conservation of angular momentum and magnetic field during the formation of a neutron star leads to the birth of rapidly rotating pulsars with a strong magnetic field B ~ 10 12 G.
It is believed that a neutron star has a magnetic field whose axis does not coincide with the axis of rotation of the star. In this case, the star's radiation (radio waves and visible light) glides across the Earth like the rays of a lighthouse. When the beam crosses the Earth, a pulse is recorded. The radiation of a neutron star itself occurs due to the fact that charged particles from the surface of the star move outward along magnetic field lines, emitting electromagnetic waves. This mechanism of pulsar radio emission, first proposed by Gold, is shown in Fig. 39.

If a beam of radiation hits an observer on earth, the radio telescope detects short pulses of radio emission with a period equal to the rotation period of the neutron star. The shape of the pulse can be very complex, which is determined by the geometry of the magnetosphere of the neutron star and is characteristic of each pulsar. The periods of rotation of pulsars are strictly constant and the accuracy of measuring these periods reaches 14-digit figures.
Currently, pulsars that are part of binary systems have been discovered. If the pulsar orbits the second component, then variations in the pulsar period should be observed due to the Doppler effect. When the pulsar approaches the observer, the recorded period of the radio pulses decreases due to the Doppler effect, and when the pulsar moves away from us, its period increases. Based on this phenomenon, pulsars that are part of double stars were discovered. For the first discovered pulsar PSR 1913 + 16, which is part of a binary system, the orbital period was 7 hours 45 minutes. The natural orbital period of the pulsar PSR 1913 + 16 is 59 ms.
The pulsar's radiation should lead to a decrease in the neutron star's rotation speed. This effect was also found. A neutron star that is part of a binary system can also be a source of intense X-ray radiation.
The structure of a neutron star with a mass of 1.4M and a radius of 16 km is shown in Fig. 40.

I is a thin outer layer of densely packed atoms. In regions II and III, the nuclei are arranged in the form of a body-centered cubic lattice. Region IV consists mainly of neutrons. In region V, matter can consist of pions and hyperons, forming the hadronic core of a neutron star. Certain details of the structure of a neutron star are currently being clarified.
The formation of neutron stars is not always a consequence of a supernova explosion. Another possible mechanism for the formation of neutron stars during the evolution of white dwarfs in close binary star systems. The flow of matter from the companion star onto the white dwarf gradually increases the mass of the white dwarf and upon reaching a critical mass (Chandrasekhar limit), the white dwarf turns into a neutron star. In the case when the flow of matter continues after the formation of a neutron star, its mass can increase significantly and, as a result of gravitational collapse, it can turn into a black hole. This corresponds to the so-called “silent” collapse.
Compact binary stars can also appear as sources of X-ray radiation. It also arises due to the accretion of matter falling from a “normal” star to a more compact one. When matter accretes onto a neutron star with B > 10 10 G, the matter falls into the region of the magnetic poles. X-ray radiation is modulated by its rotation around its axis. Such sources are called X-ray pulsars.
There are X-ray sources (called bursters) in which bursts of radiation occur periodically at intervals of several hours to a day. The characteristic rise time of the burst is 1 second. Burst duration is from 3 to 10 seconds. The intensity at the moment of the burst can be 2 - 3 orders of magnitude higher than the luminosity in a quiet state. Currently, several hundred such sources are known. It is believed that the bursts of radiation occur as a result of thermonuclear explosions of matter accumulated on the surface of a neutron star as a result of accretion.
It is well known that at small distances between nucleons (< 0.3·10 -13 см) ядерные силы притяжения сменяются силами оттал-кивания, т. е. противодействие ядерного вещества на малых расстояниях сжимающей силе тяготения увеличивается. Если плотность вещества в центре нейтронной звезды превышает ядерную плотность ρ яд и достигает 10 15 г/см 3 , то в центре звезды наряду с нуклонами и электронами образуются также мезоны, гипероны и другие более массивные частицы. Исследования поведения вещества при плотностях, превышающих ядерную плотность, в настоящее время находятся в начальной стадии и имеется много нерешенных проблем. Расчеты показывают, что при плотностях вещества ρ >ρ poison such processes as the appearance of pion condensate, the transition of neutronized matter into a solid crystalline state, and the formation of hyperon and quark-gluon plasma are possible. The formation of superfluid and superconducting states of neutron matter is possible.
In accordance with modern ideas about the behavior of matter at densities 10 2 - 10 3 times higher than nuclear (namely, such densities are discussed when the internal structure of a neutron star is discussed), atomic nuclei are formed inside the star near the stability limit. A deeper understanding can be achieved by studying the state of matter depending on the density, temperature, stability of nuclear matter at exotic ratios of the number of protons to the number of neutrons in the nucleus n p / n n , taking into account weak processes involving neutrinos. At present, practically the only possibility of studying matter at densities higher than nuclear ones is nuclear reactions between heavy ions. However, experimental data on collisions of heavy ions still provide insufficient information, since the achievable values ​​of n p / n n for both the target nucleus and the incident accelerated nucleus are small (~ 1 - 0.7).
Accurate measurements of the periods of radio pulsars have shown that the neutron star's rotation speed is gradually slowing down. This is due to the transition of the kinetic energy of the star's rotation into the radiation energy of the pulsar and the emission of neutrinos. Small abrupt changes in the periods of radio pulsars are explained by the accumulation of stress in the surface layer of the neutron star, accompanied by “cracking” and “fractures,” which leads to a change in the rotation speed of the star. The observed time characteristics of radio pulsars contain information about the properties of the “crust” of the neutron star, the physical conditions inside it, and the superfluidity of neutron matter. Recently, a significant number of radio pulsars with periods less than 10 ms have been discovered. This requires clarification of ideas about the processes occurring in neutron stars.
Another problem is the study of neutrino processes in neutron stars. Neutrino emission is one of the mechanisms by which a neutron star loses energy within 10 5 - 10 6 years after its formation.

“The remains of the exploded core are known as a neutron star. Neutron stars spin very quickly, emitting light and radio waves that, when passing by the Earth, seem like the light of a cosmic beacon.

Fluctuations in the brightness of these waves led astronomers to call such stars pulsars. The fastest pulsars spin at almost 1,000 revolutions per second." (1)

“To date, more than two hundred have been opened. By recording the radiation of pulsars at different but similar frequencies, it was possible to determine the distance to them from the delay of the signal at a longer wavelength (assuming a certain plasma density in the interstellar medium). It turned out that all pulsars are located at distances from 100 to 25,000 light years, i.e., they belong to our Galaxy, grouping near the plane of the Milky Way (Fig. 7).” (2)

Black holes

“If a star has twice the mass of the Sun, then towards the end of its life the star may explode as a supernova, but if the mass of the material remaining after the explosion is still greater than twice the Sun, then the star should collapse into a dense tiny body, since gravitational forces are entirely suppress any resistance to compression. Scientists believe that it is at this moment that a catastrophic gravitational collapse leads to the emergence of a black hole. They believe that with the end of thermonuclear reactions, the star can no longer be in a stable state. Then for a massive star there remains one inevitable path: the path of general and complete compression (collapse), turning it into an invisible black hole.

In 1939, R. Oppenheimer and his graduate student Snyder at the University of California (Berkeley) were engaged in elucidating the final fate of a large mass of cold matter. One of the most impressive consequences of Einstein's general theory of relativity turned out to be the following: when a large mass begins to collapse, this process cannot be stopped and the mass collapses into a black hole. If, for example, a non-rotating symmetrical star begins to shrink to a critical size known as the gravitational radius, or Schwarzschild radius (named after Karl Schwarzschild, who first pointed out its existence). If a star reaches this radius, then nothing can prevent it from completing its collapse, that is, literally closing in on itself.

What are the physical properties of “black holes” and how do scientists expect to detect these objects? Many scientists have pondered these questions; Some answers have been received that can help in the search for such objects.

The name itself - black holes - suggests that this is a class of objects that cannot be seen. Their gravitational field is so strong that if somehow it were possible to get close to a black hole and direct the beam of the most powerful searchlight away from its surface, then it would be impossible to see this searchlight even from a distance not exceeding the distance from the Earth to the Sun. Indeed, even if we could concentrate all the light of the Sun in this powerful spotlight, we would not see it, since the light would not be able to overcome the influence of the gravitational field of the black hole on it and leave its surface. That is why such a surface is called the absolute event horizon. It represents the boundary of a black hole.

Scientists note that these unusual objects are not easy to understand while remaining within the framework of Newton's law of gravity. Near the surface of a black hole, gravity is so strong that the usual Newtonian laws cease to apply here. They should be replaced by the laws of Einstein's general theory of relativity. According to one of the three consequences of Einstein's theory, when light leaves a massive body, it should experience a red shift, since it loses energy to overcome the gravitational field of the star. Radiation coming from a dense star like the white dwarf satellite of Sirius A is only slightly redshifted. The denser the star, the greater this shift, so that no radiation in the visible region of the spectrum will come from a super-dense star. But if the gravitational effect of a star increases as a result of its compression, then the gravitational forces turn out to be so great that light cannot leave the star at all. Thus, for any observer the possibility of seeing the black hole is completely excluded! But then the question naturally arises: if it is not visible, then how can we detect it? To answer this question, scientists resort to clever tricks. Ruffini and Wheeler thoroughly studied this problem and proposed several ways, if not to see, but at least to detect a black hole. To begin with, when a black hole is born through the process of gravitational collapse, it should emit gravitational waves that could traverse space at the speed of light and briefly distort the geometry of space near Earth. This distortion would manifest itself in the form of gravitational waves acting simultaneously on identical instruments installed on the ground surface at a considerable distance from each other. Gravitational radiation could come from stars undergoing gravitational collapse. If during normal life the star rotated, then, shrinking and becoming smaller and smaller, it will rotate faster and faster, maintaining its angular momentum. Finally, it can reach a stage when the speed of movement at its equator approaches the speed of light, that is, the maximum possible speed. In this case, the star would be highly deformed and could eject some of the matter. With such a deformation, energy could escape from the star in the form of gravitational waves with a frequency of about a thousand vibrations per second (1000 Hz).

Roger Penrose, professor of mathematics at Birkbeck College, University of London, looked at the curious case of black hole collapse and formation. He admits that the black hole disappears and then appears at another time in some other universe. In addition, he argues that the birth of a black hole during gravitational collapse is an important indication that something unusual is happening to the geometry of spacetime. Penrose's research shows that the collapse ends with the formation of a singularity (from the Latin singularius - separate, single), that is, it should continue to zero dimensions and infinite density of the object. The last condition makes it possible for another universe to approach our singularity, and it is possible that the singularity will pass into this new universe. It may even appear in some other place in our own Universe.

Some scientists view the formation of a black hole as a small model of what general relativity predicts will eventually happen to the universe. It is generally accepted that we can in an ever-expanding Universe, and one of the most important and pressing questions of science concerns the nature of the Universe, its past and future. Without a doubt, all modern observational results point to the expansion of the Universe. However, today one of the most tricky questions is this: is the rate of this expansion slowing down, and if so, will the Universe contract in tens of billions of years, forming a singularity. Apparently, someday we will be able to figure out which path the Universe follows, but perhaps much earlier, by studying the information that leaks out at the birth of black holes, and the physical laws that govern their fate, we will be able to predict their final fate Universe (Fig. 8)". (1)