Due to the relatively recent rise in interest in making popular science films about space exploration, the modern viewer has heard a lot about such phenomena as the singularity, or black hole. However, films obviously do not reveal the full nature of these phenomena, and sometimes even distort the constructed scientific theories for greater effect. For this reason, the presentation of many modern people about these phenomena either completely superficially, or completely erroneously. One of the solutions to the problem that has arisen is this article, in which we will try to understand the existing research results and answer the question - what is a black hole?

In 1784, the English priest and naturalist John Michell first mentioned in a letter to the Royal Society a hypothetical massive body that has such a strong gravitational attraction that the second cosmic velocity for it would exceed the speed of light. The second cosmic velocity is the speed that a relatively small object will need to overcome the gravitational attraction of a celestial body and go beyond the limits of a closed orbit around this body. According to his calculations, a body with the density of the Sun and with a radius of 500 solar radii will have on its surface a second cosmic velocity equal to the speed of light. In this case, even light will not leave the surface of such a body, and therefore given body will only absorb the incoming light and remain invisible to the observer - a kind of black spot against the background of dark space.

However, the concept of a supermassive body proposed by Michell did not attract much interest until the work of Einstein. Recall that the latter defined the speed of light as the limiting speed of information transfer. In addition, Einstein expanded the theory of gravity for speeds close to the speed of light (). As a result, it was no longer relevant to apply the Newtonian theory to black holes.

Einstein's equation

As a result of applying general relativity to black holes and solving the Einstein equations, the main parameters of a black hole were revealed, of which there are only three: mass, electric charge and angular momentum. It should be noted the significant contribution of the Indian astrophysicist Subramanyan Chandrasekhar, who created a fundamental monograph: "The Mathematical Theory of Black Holes".

Thus, the solution of the Einstein equations is represented by four options for four possible types black holes:

• A black hole without rotation and without a charge is the Schwarzschild solution. One of the first descriptions of a black hole (1916) using Einstein's equations, but without taking into account two of the three parameters of the body. The solution of the German physicist Karl Schwarzschild allows you to calculate the external gravitational field of a spherical massive body. A feature of the German scientist's concept of black holes is the presence of an event horizon and the one behind it. Schwarzschild also first calculated the gravitational radius, which received his name, which determines the radius of the sphere on which the event horizon would be located for a body with a given mass.
• A black hole without rotation with a charge is the Reisner-Nordström solution. A solution put forward in 1916-1918, taking into account the possible electric charge of a black hole. This charge cannot be arbitrarily large and is limited due to the resulting electrical repulsion. The latter must be compensated by gravitational attraction.
• A black hole with rotation and no charge - Kerr's solution (1963). A rotating Kerr black hole differs from a static one by the presence of the so-called ergosphere (read more about this and other components of a black hole).
• BH with rotation and charge - Kerr-Newman solution. This solution was calculated in 1965 and on this moment is the most complete, since it takes into account all three BH parameters. However, it is still assumed that black holes in nature have an insignificant charge.

The formation of a black hole

There are several theories about how a black hole is formed and appears, the most famous of which is the emergence of a star with sufficient mass as a result of gravitational collapse. Such compression can end the evolution of stars with a mass of more than three solar masses. At the end of the thermo nuclear reactions inside such stars, they begin to rapidly shrink into a superdense one. If the pressure of the gas of a neutron star cannot compensate for the gravitational forces, that is, the mass of the star overcomes the so-called. Oppenheimer-Volkov limit, then the collapse continues, causing matter to shrink into a black hole.

The second scenario describing the birth of a black hole is the compression of protogalactic gas, that is, interstellar gas that is at the stage of transformation into a galaxy or some kind of cluster. In the case of insufficient internal pressure to compensate for the same gravitational forces, a black hole can arise.

Two other scenarios remain hypothetical:

• The occurrence of a black hole as a result - the so-called. primordial black holes.
• Occurrence as a result of nuclear reactions at high energies. An example of such reactions is experiments on colliders.

Structure and physics of black holes

The structure of a black hole according to Schwarzschild includes only two elements that were mentioned earlier: the singularity and the event horizon of a black hole. Briefly speaking about the singularity, it can be noted that it is impossible to draw a straight line through it, and also that most of the existing physical theories do not work inside it. Thus, the physics of the singularity remains a mystery to scientists today. of a black hole is a certain boundary, crossing which, a physical object loses the ability to return back beyond its limits and unambiguously “falls” into the singularity of a black hole.

The structure of a black hole becomes somewhat more complicated in the case of the Kerr solution, namely, in the presence of BH rotation. Kerr's solution implies that the hole has an ergosphere. Ergosphere - a certain area located outside the event horizon, inside which all bodies move in the direction of rotation of the black hole. This area is not yet exciting and it is possible to leave it, unlike the event horizon. The ergosphere is probably a kind of analogue of an accretion disk, which represents a rotating substance around massive bodies. If a static Schwarzschild black hole is represented as a black sphere, then the Kerry black hole, due to the presence of an ergosphere, has the shape of an oblate ellipsoid, in the form of which we often saw black holes in drawings, in old movies or video games.

• How much does a black hole weigh? – The largest theoretical material on the appearance of a black hole is available for the scenario of its appearance as a result of the collapse of a star. In this case, the maximum mass of a neutron star and the minimum mass of a black hole are determined by the Oppenheimer - Volkov limit, according to which the lower limit of the BH mass is 2.5 - 3 solar masses. The heaviest black hole ever discovered (in the galaxy NGC 4889) has a mass of 21 billion solar masses. However, one should not forget about black holes, hypothetically resulting from nuclear reactions at high energies, such as those at colliders. The mass of such quantum black holes, in other words "Planck black holes" is of the order of , namely 2 10 −5 g.
• Black hole size. The minimum BH radius can be calculated from the minimum mass (2.5 – 3 solar masses). If the gravitational radius of the Sun, that is, the area where the event horizon would be, is about 2.95 km, then the minimum radius of a BH of 3 solar masses will be about nine kilometers. Such relatively small sizes do not fit in the head when it comes to massive objects that attract everything around. However, for quantum black holes, the radius is -10 −35 m.
• The average density of a black hole depends on two parameters: mass and radius. The density of a black hole with a mass of about three solar masses is about 6 10 26 kg/m³, while the density of water is 1000 kg/m³. However, such small black holes have not been found by scientists. Most of the detected BHs have masses greater than 105 solar masses. There is an interesting pattern according to which the more massive the black hole, the lower its density. In this case, a change in mass by 11 orders of magnitude entails a change in density by 22 orders of magnitude. Thus, a black hole with a mass of 1 ·10 9 solar masses has a density of 18.5 kg/m³, which is one less than the density of gold. And black holes with a mass of more than 10 10 solar masses can have an average density less than the density of air. Based on these calculations, it is logical to assume that the formation of a black hole occurs not due to the compression of matter, but as a result of the accumulation of a large amount of matter in a certain volume. In the case of quantum black holes, their density can be about 10 94 kg/m³.
• The temperature of a black hole is also inversely proportional to its mass. This temperature is directly related to . The spectrum of this radiation coincides with the spectrum of a completely black body, that is, a body that absorbs all incident radiation. The radiation spectrum of a black body depends only on its temperature, then the temperature of a black hole can be determined from the Hawking radiation spectrum. As mentioned above, this radiation is the more powerful, the smaller the black hole. At the same time, Hawking radiation remains hypothetical, since it has not yet been observed by astronomers. It follows from this that if Hawking radiation exists, then the temperature of the observed BHs is so low that it does not allow one to detect the indicated radiation. According to calculations, even the temperature of a hole with a mass of the order of the mass of the Sun is negligibly small (1 10 -7 K or -272°C). The temperature of quantum black holes can reach about 10 12 K, and with their rapid evaporation (about 1.5 min.), Such BHs can emit energy of the order of ten million atomic bombs. But, fortunately, the creation of such hypothetical objects will require energy 10 14 times greater than that achieved today at the Large Hadron Collider. In addition, such phenomena have never been observed by astronomers.

What is a CHD made of?

Another question worries both scientists and those who are simply fond of astrophysics - what does a black hole consist of? There is no single answer to this question, since it is not possible to look beyond the event horizon surrounding any black hole. In addition, as mentioned earlier, the theoretical models of a black hole provide for only 3 of its components: the ergosphere, the event horizon, and the singularity. It is logical to assume that in the ergosphere there are only those objects that were attracted by the black hole, and which now revolve around it - various kinds of cosmic bodies and cosmic gas. The event horizon is just a thin implicit border, once beyond which, the same cosmic bodies are irrevocably attracted towards the last main component of the black hole - the singularity. The nature of the singularity has not been studied today, and it is too early to talk about its composition.

According to some assumptions, a black hole may consist of neutrons. If we follow the scenario of the occurrence of a black hole as a result of the compression of a star to a neutron star with its subsequent compression, then, probably, the main part of the black hole consists of neutrons, of which the neutron star itself consists. In simple words: When a star collapses, its atoms are compressed in such a way that electrons combine with protons, thereby forming neutrons. Such a reaction does indeed take place in nature, with the formation of a neutron, neutrino emission occurs. However, these are just guesses.

What happens if you fall into a black hole?

Falling into an astrophysical black hole leads to stretching of the body. Consider a hypothetical suicide astronaut heading into a black hole wearing nothing but a space suit, feet first. Crossing the event horizon, the astronaut will not notice any changes, despite the fact that he no longer has the opportunity to get back. At some point, the astronaut will reach a point (slightly behind the event horizon) where the deformation of his body will begin to occur. Since the gravitational field of a black hole is non-uniform and is represented by a force gradient increasing towards the center, the astronaut's legs will be subjected to a noticeably greater gravitational effect than, for example, the head. Then, due to gravity, or rather, tidal forces, the legs will “fall” faster. Thus, the body begins to gradually stretch in length. To describe this phenomenon, astrophysicists have come up with a rather creative term - spaghettification. Further stretching of the body will probably decompose it into atoms, which, sooner or later, will reach a singularity. One can only guess how a person will feel in this situation. It is worth noting that the effect of stretching the body is inversely proportional to the mass of the black hole. That is, if a BH with the mass of three Suns instantly stretches/breaks the body, then the supermassive black hole will have lower tidal forces and, there are suggestions that some physical materials could “tolerate” such a deformation without losing their structure.

As you know, near massive objects, time flows more slowly, which means that time for a suicide astronaut will flow much more slowly than for earthlings. In that case, perhaps he will outlive not only his friends, but the Earth itself. Calculations will be required to determine how much time will slow down for an astronaut, but from the above it can be assumed that the astronaut will fall into the black hole very slowly and may simply not live to see the moment when his body begins to deform.

It is noteworthy that for an observer outside, all bodies that have flown up to the event horizon will remain at the edge of this horizon until their image disappears. The reason for this phenomenon is the gravitational redshift. Simplifying somewhat, we can say that the light falling on the body of a suicide astronaut "frozen" at the event horizon will change its frequency due to its slowed down time. As time passes more slowly, the frequency of light will decrease and the wavelength will increase. As a result of this phenomenon, at the output, that is, for an external observer, the light will gradually shift towards the low-frequency - red. A shift of light along the spectrum will take place, as the suicide astronaut moves further and further away from the observer, albeit almost imperceptibly, and his time flows more and more slowly. Thus, the light reflected by his body will soon go beyond the visible spectrum (the image will disappear), and in the future the astronaut's body can only be detected in the infrared region, later in the radio frequency region, and as a result, the radiation will be completely elusive.

Despite what has been written above, it is assumed that in very large supermassive black holes, tidal forces do not change so much with distance and act almost uniformly on the falling body. In this case, the falling spaceship would retain its structure. A reasonable question arises - where does the black hole lead? This question can be answered by the work of some scientists, linking two such phenomena as wormholes and black holes.

Back in 1935, Albert Einstein and Nathan Rosen, taking into account, put forward a hypothesis about the existence of so-called wormholes, connecting two points of space-time by way in places of significant curvature of the latter - the Einstein-Rosen bridge or wormhole. For such a powerful curvature of space, bodies with a gigantic mass will be required, with the role of which black holes would perfectly cope.

The Einstein-Rosen Bridge is considered an impenetrable wormhole, as it is small and unstable.

A traversable wormhole is possible within the theory of black and white holes. Where the white hole is the output of information that fell into the black hole. The white hole is described in the framework of general relativity, but today it remains hypothetical and has not been discovered. Another model of a wormhole was proposed by American scientists Kip Thorne and his graduate student Mike Morris, which can be passable. However, as in the case of the Morris-Thorn wormhole, as well as in the case of black and white holes, the possibility of travel requires the existence of so-called exotic matter, which has negative energy and also remains hypothetical.

Black holes in the universe

The existence of black holes was confirmed relatively recently (September 2015), but before that time there was already a lot of theoretical material on the nature of black holes, as well as many candidate objects for the role of a black hole. First of all, one should take into account the dimensions of the black hole, since the very nature of the phenomenon depends on them:

• stellar mass black hole. Such objects are formed as a result of the collapse of a star. As mentioned earlier, the minimum mass of a body capable of forming such a black hole is 2.5 - 3 solar masses.
• Black holes medium weight . Conditional intermediate type black holes that have grown larger due to the absorption of nearby objects, such as gas accumulations, a neighboring star (in systems of two stars) and other cosmic bodies.
• Supermassive black hole. Compact objects with 10 5 -10 10 solar masses. Distinctive properties Such BHs are paradoxically low density, as well as weak tidal forces, which were discussed earlier. It is this supermassive black hole at the center of our Milky Way galaxy (Sagittarius A*, Sgr A*), as well as most other galaxies.

Candidates for CHD

The nearest black hole, or rather a candidate for the role of a black hole, is an object (V616 Unicorn), which is located at a distance of 3000 light years from the Sun (in our galaxy). It consists of two components: a star with a mass of half the solar mass, as well as an invisible small body, the mass of which is 3-5 solar masses. If this object turns out to be a small black hole of stellar mass, then by right it will be the nearest black hole.

Following this object, the second closest black hole is Cyg X-1 (Cyg X-1), which was the first candidate for the role of a black hole. The distance to it is approximately 6070 light years. Quite well studied: it has a mass of 14.8 solar masses and an event horizon radius of about 26 km.

According to some sources, another closest candidate for the role of a black hole may be a body in the star system V4641 Sagittarii (V4641 Sgr), which, according to estimates in 1999, was located at a distance of 1600 light years. However, subsequent studies increased this distance by at least 15 times.

How many black holes are in our galaxy?

There is no exact answer to this question, since it is rather difficult to observe them, and during the entire study of the sky, scientists managed to detect about a dozen black holes within the Milky Way. Without indulging in calculations, we note that in our galaxy there are about 100 - 400 billion stars, and about every thousandth star has enough mass to form a black hole. It is likely that millions of black holes could have formed during the existence of the Milky Way. Since it is easier to register huge black holes, it is logical to assume that most of the BHs in our galaxy are not supermassive. It is noteworthy that NASA research in 2005 suggests the presence of a whole swarm of black holes (10-20 thousand) orbiting the center of the galaxy. In addition, in 2016, Japanese astrophysicists discovered a massive satellite near the object * - a black hole, the core of the Milky Way. Due to the small radius (0.15 light years) of this body, as well as its huge mass (100,000 solar masses), scientists suggest that this object is also a supermassive black hole.

The core of our galaxy, the black hole of the Milky Way (Sagittarius A *, Sgr A * or Sagittarius A *) is supermassive and has a mass of 4.31 10 6 solar masses, and a radius of 0.00071 light years (6.25 light hours or 6.75 billion km). The temperature of Sagittarius A* together with the cluster around it is about 1 10 7 K.

The biggest black hole

The largest black hole in the universe that scientists have been able to detect is a supermassive black hole, the FSRQ blazar, at the center of the galaxy S5 0014+81, at a distance of 1.2·10 10 light-years from Earth. According to preliminary results of observation, using the Swift space observatory, the mass of the black hole was 40 billion (40 10 9) solar masses, and the Schwarzschild radius of such a hole was 118.35 billion kilometers (0.013 light years). In addition, according to calculations, it arose 12.1 billion years ago (1.6 billion years after the Big Bang). If this giant black hole does not absorb the matter surrounding it, then it will live to see the era of black holes - one of the eras in the development of the Universe, during which black holes will dominate in it. If the core of the galaxy S5 0014+81 continues to grow, then it will become one of the last black holes that will exist in the Universe.

The other two known black holes, though not named, have highest value for the study of black holes, since they confirmed their existence experimentally, and also gave important results for the study of gravity. We are talking about the event GW150914, which is called the collision of two black holes into one. This event allowed to register .

Detection of black holes

Before considering methods for detecting black holes, one should answer the question - why is a black hole black? - the answer to it does not require deep knowledge in astrophysics and cosmology. The fact is that a black hole absorbs all the radiation falling on it and does not radiate at all, if you do not take into account the hypothetical. If we consider this phenomenon in more detail, we can assume that there are no processes inside black holes that lead to the release of energy in the form of electromagnetic radiation. Then if the black hole radiates, then it is in the Hawking spectrum (which coincides with the spectrum of a heated, absolutely black body). However, as mentioned earlier, this radiation was not detected, which suggests a completely low temperature of black holes.

Another generally accepted theory says that electromagnetic radiation is not at all capable of leaving the event horizon. It is most likely that photons (particles of light) are not attracted by massive objects, since, according to the theory, they themselves have no mass. However, the black hole still "attracts" the photons of light through the distortion of space-time. If we imagine a black hole in space as a kind of depression on the smooth surface of space-time, then there is a certain distance from the center of the black hole, approaching which the light will no longer be able to move away from it. That is, roughly speaking, the light begins to "fall" into the "pit", which does not even have a "bottom".

In addition, if we take into account the effect of gravitational redshift, it is possible that light in a black hole loses its frequency, shifting along the spectrum to the region of low-frequency long-wave radiation, until it loses energy altogether.

So, a black hole is black and therefore difficult to detect in space.

Detection methods

Consider the methods that astronomers use to detect a black hole:

In addition to the methods mentioned above, scientists often associate objects such as black holes and. Quasars are some clusters of cosmic bodies and gas, which are among the brightest astronomical objects in the Universe. Since they have a high intensity of luminescence at relatively small sizes, there is reason to believe that the center of these objects is a supermassive black hole, which attracts the surrounding matter to itself. Due to such a powerful gravitational attraction, the attracted matter is so heated that it radiates intensely. The detection of such objects is usually compared with the detection of a black hole. Sometimes quasars can emit jets of heated plasma in two directions - relativistic jets. The reasons for the emergence of such jets (jet) are not completely clear, but they are probably caused by the interaction of the magnetic fields of the BH and the accretion disk, and are not emitted by a direct black hole.

A jet in the M87 galaxy hitting from the center of a black hole

Summing up the above, one can imagine, up close: it is a spherical black object, around which strongly heated matter rotates, forming a luminous accretion disk.

Merging and colliding black holes

One of the most interesting phenomena in astrophysics is the collision of black holes, which also makes it possible to detect such massive astronomical bodies. Such processes are of interest not only to astrophysicists, since they result in phenomena poorly studied by physicists. The brightest example is the previously mentioned event called GW150914, when two black holes approached so much that, as a result of mutual gravitational attraction, they merged into one. An important consequence of this collision was the emergence of gravitational waves.

According to the definition of gravitational waves, these are changes in the gravitational field that propagate in a wave-like manner from massive moving objects. When two such objects approach each other, they begin to rotate around a common center of gravity. As they approach each other, their rotation around their own axis increases. Such variable oscillations of the gravitational field at some point can form one powerful gravitational wave that can propagate in space for millions of light years. So, at a distance of 1.3 billion light years, a collision of two black holes occurred, which formed a powerful gravitational wave that reached the Earth on September 14, 2015 and was recorded by the LIGO and VIRGO detectors.

How do black holes die?

Obviously, for a black hole to cease to exist, it would need to lose all of its mass. However, according to her definition, nothing can leave the black hole if it has crossed its event horizon. It is known that for the first time the Soviet theoretical physicist Vladimir Gribov mentioned the possibility of emission of particles by a black hole in his discussion with another Soviet scientist Yakov Zeldovich. He argued that from the point of view of quantum mechanics, a black hole is capable of emitting particles through a tunnel effect. Later, with the help of quantum mechanics, he built his own, somewhat different theory, the English theoretical physicist Stephen Hawking. You can read more about this phenomenon. In short, there are so-called virtual particles in vacuum, which are constantly born in pairs and annihilate each other, while not interacting with the surrounding world. But if such pairs arise at the black hole's event horizon, then strong gravity is hypothetically able to separate them, with one particle falling into the black hole, and the other going away from the black hole. And since a particle that has flown away from a hole can be observed, and therefore has positive energy, a particle that has fallen into a hole must have negative energy. Thus, the black hole will lose its energy and there will be an effect called black hole evaporation.

According to the available models of a black hole, as mentioned earlier, as its mass decreases, its radiation becomes more intense. Then, at the final stage of the existence of a black hole, when it may be reduced to the size of a quantum black hole, it will release a huge amount of energy in the form of radiation, which can be equivalent to thousands or even millions of atomic bombs. This event is somewhat reminiscent of the explosion of a black hole, like the same bomb. According to calculations, primordial black holes could have been born as a result of the Big Bang, and those of them, the mass of which is on the order of 10 12 kg, should have evaporated and exploded around our time. Be that as it may, such explosions have never been seen by astronomers.

Despite the mechanism proposed by Hawking for the destruction of black holes, the properties of Hawking radiation cause a paradox in the framework of quantum mechanics. If a black hole absorbs some body, and then loses the mass resulting from the absorption of this body, then regardless of the nature of the body, the black hole will not differ from what it was before the absorption of the body. In this case, information about the body is forever lost. From the point of view of theoretical calculations, the transformation of the initial pure state into the resulting mixed (“thermal”) state does not correspond to the current theory of quantum mechanics. This paradox is sometimes called the disappearance of information in a black hole. A real solution to this paradox has never been found. Known options for solving the paradox:

• Inconsistency of Hawking's theory. This entails the impossibility of destroying the black hole and its constant growth.
• The presence of white holes. In this case, the absorbed information does not disappear, but is simply thrown out into another Universe.
• Inconsistency of the generally accepted theory of quantum mechanics.

Unsolved problem of black hole physics

Judging by everything that was described earlier, black holes, although they have been studied for a relatively long time, still have many features, the mechanisms of which are still not known to scientists.

• In 1970, an English scientist formulated the so-called. "principle of cosmic censorship" - "Nature abhors the bare singularity." This means that the singularity is formed only in places hidden from view, like the center of a black hole. However, this principle has not yet been proven. There are also theoretical calculations according to which a "naked" singularity can occur.
• The “no-hair theorem”, according to which black holes have only three parameters, has not been proven either.
• A complete theory of the black hole magnetosphere has not been developed.
• The nature and physics of the gravitational singularity has not been studied.
• It is not known for certain what happens at the final stage of the existence of a black hole, and what remains after its quantum decay.

Interesting facts about black holes

Summarizing the above, we can highlight several interesting and unusual features nature of black holes:

• Black holes have only three parameters: mass, electric charge and angular momentum. As a result of such a small number of characteristics of this body, the theorem stating this is called the "no-hair theorem". This is also where the phrase “a black hole has no hair” came from, which means that two black holes are absolutely identical, their three parameters mentioned are the same.
• The density of black holes can be less than the density of air, and the temperature is close to absolute zero. From this we can assume that the formation of a black hole occurs not due to the compression of matter, but as a result of the accumulation of a large amount of matter in a certain volume.
• Time for bodies absorbed by black holes goes much slower than for an external observer. In addition, the absorbed bodies are significantly stretched inside the black hole, which has been called spaghettification by scientists.
• There may be about a million black holes in our galaxy.
• There is probably a supermassive black hole at the center of every galaxy.
• In the future, according to the theoretical model, the Universe will reach the so-called era of black holes, when black holes will become the dominant bodies in the Universe.

Black holes, dark matter, dark matter... These are undoubtedly the strangest and most mysterious objects in space. Their bizarre properties can defy the laws of physics in the universe and even the nature of existing reality. To understand what black holes are, scientists offer to “change landmarks”, learn to think outside the box and apply a little imagination. Black holes are formed from the cores of super massive stars, which can be described as a region of space where a huge mass is concentrated in the void, and nothing, not even light, can escape the gravitational attraction there. This is the area where the second space velocity exceeds the speed of light: And the more massive the object of motion, the faster it must move in order to get rid of its gravity. This is known as the second escape velocity.

The Collier Encyclopedia calls a black hole a region in space that has arisen as a result of a complete gravitational collapse of matter, in which the gravitational attraction is so strong that neither matter, nor light, nor other information carriers can leave it. Therefore, the interior of a black hole is causally unrelated to the rest of the universe; physical processes occurring inside a black hole cannot affect processes outside it. A black hole is surrounded by a surface with the property of a unidirectional membrane: matter and radiation freely fall through it into the black hole, but nothing can escape from it. This surface is called the "event horizon".

Discovery history

Black holes, predicted by general relativity (the theory of gravity proposed by Einstein in 1915) and others, are more modern theories gravitation were mathematically substantiated by R. Oppenheimer and H. Snyder in 1939. But the properties of space and time in the vicinity of these objects turned out to be so unusual that astronomers and physicists did not take them seriously for 25 years. However, astronomical discoveries in the mid-1960s forced us to look at black holes as a possible physical reality. New discoveries and studies can fundamentally change our understanding of space and time, shedding light on billions of cosmic mysteries.

Formation of black holes

While thermonuclear reactions take place in the interior of the star, they maintain high temperature and pressure, preventing the star from collapsing under the influence of its own gravity. However, over time, the nuclear fuel is depleted, and the star begins to shrink. Calculations show that if the mass of a star does not exceed three solar masses, then it will win the “battle with gravity”: its gravitational collapse will be stopped by the pressure of “degenerate” matter, and the star will forever turn into a white dwarf or neutron star. But if the mass of a star is more than three solar, then nothing can stop its catastrophic collapse and it will quickly go under the event horizon, becoming a black hole.

Is a black hole a donut hole?

Anything that doesn't emit light is hard to see. One way to search for a black hole is to look for regions in open space, which have a large mass and are located in a dark space. When searching for these types of objects, astronomers have found them in two main areas: at the centers of galaxies and in binary star systems in our galaxy. In total, as scientists suggest, there are tens of millions of such objects.

At present, the only reliable way to distinguish a black hole from another type of object is to measure the mass and size of the object and compare its radius with

Every person who gets acquainted with astronomy sooner or later experiences a strong curiosity about the most mysterious objects in the universe - black holes. These are the real masters of darkness, capable of "swallowing" any atom passing nearby and not letting even light escape - their attraction is so powerful. These objects present a real challenge for physicists and astronomers. The former still cannot understand what happens to the matter that has fallen inside the black hole, and the latter, although they explain the most energy-consuming phenomena of space by the existence of black holes, have never had the opportunity to observe any of them directly. We will talk about these most interesting celestial objects, find out what has already been discovered and what remains to be known in order to lift the veil of secrecy.

What is a black hole?

The name "black hole" (in English - black hole) was proposed in 1967 by the American theoretical physicist John Archibald Wheeler (see photo on the left). It served to designate a celestial body, the attraction of which is so strong that even light does not let go of itself. Therefore, it is "black" because it does not emit light.

indirect observations

This is the reason for such mystery: since black holes do not glow, we cannot see them directly and are forced to look for and study them, using only indirect evidence that their existence leaves in the surrounding space. In other words, if a black hole engulfs a star, we can't see the black hole, but we can observe the devastating effects of its powerful gravitational field.

Laplace's intuition

Despite the fact that the expression "black hole" to denote the hypothetical final stage of the evolution of a star that collapsed into itself under the influence of gravity appeared relatively recently, the idea of ​​the possibility of the existence of such bodies arose more than two centuries ago. The Englishman John Michell and the Frenchman Pierre-Simon de Laplace independently hypothesized the existence of "invisible stars"; while they were based on the usual laws of dynamics and the law gravity Newton. Today black holes got their correct description based general theory Einstein's relativity.

In his work An Account of the System of the World (1796), Laplace wrote: Bright Star the same density as the Earth, with a diameter 250 times the diameter of the Sun, due to its gravitational attraction would not allow light rays to reach us. Therefore, it is possible that the largest and brightest celestial bodies are invisible for this reason.

Invincible Gravity

Laplace's idea was based on the concept of escape velocity (second cosmic velocity). A black hole is such a dense object that its attraction is able to detain even light, which develops the highest speed in nature (almost 300,000 km / s). In practice, in order to escape from a black hole, you need a speed faster than the speed of light, but this is impossible!

This means that a star of this kind would be invisible, since even light would not be able to overcome its powerful gravity. Einstein explained this fact through the phenomenon of light deflection under the influence of a gravitational field. In reality, near a black hole, space-time is so curved that the paths of light rays also close on themselves. In order to turn the Sun into a black hole, we will have to concentrate all its mass in a ball with a radius of 3 km, and the Earth will have to turn into a ball with a radius of 9 mm!

Types of black holes

About ten years ago, observations suggested the existence of two types of black holes: stellar, whose mass is comparable to the mass of the Sun or slightly exceeds it, and supermassive, whose mass is from several hundred thousand to many millions of solar masses. However, relatively recently, high-resolution X-ray images and spectra obtained with artificial satellites such as "Chandra" and "HMM-Newton", brought to the fore the third type of black hole - with a mass of average magnitude, exceeding the mass of the Sun by thousands of times.

stellar black holes

Stellar black holes became known earlier than others. They form when a high-mass star at the end of its evolutionary path runs out of nuclear fuel and collapses into itself due to its own gravity. A star-shattering explosion (this phenomenon is known as a “supernova explosion”) has catastrophic consequences: if the core of a star exceeds the mass of the Sun by more than 10 times, no nuclear force unable to withstand the gravitational collapse that would result in a black hole.

Supermassive black holes

Supermassive black holes, first noted in the nuclei of some active galaxies, have a different origin. There are several hypotheses regarding their birth: a stellar black hole that devours all the stars surrounding it for millions of years; a merged cluster of black holes; a colossal cloud of gas collapsing directly into a black hole. These black holes are among the most energetic objects in space. They are located in the centers of very many galaxies, if not all. Our Galaxy also has such a black hole. Sometimes, due to the presence of such a black hole, the cores of these galaxies become very bright. Galaxies with black holes in the center, surrounded by a large amount of falling matter and, therefore, capable of producing an enormous amount of energy, are called "active", and their nuclei are called "active galactic nuclei" (AGN). For example, quasars (the most distant space objects from us available to our observation) are active galaxies, in which we see only a very bright nucleus.

Medium and "mini"

Another mystery remains the medium-mass black holes, which, according to recent studies, may be at the center of some globular clusters, such as M13 and NCC 6388. Many astronomers are skeptical about these objects, but some latest research suggest the presence of medium-sized black holes even near the center of our Galaxy. English physicist Stephen Hawking also put forward a theoretical assumption about the existence of the fourth type of black hole - a "mini-hole" with a mass of only a billion tons (which is approximately equal to the mass of a large mountain). It's about about primary objects, that is, those that appeared in the first moments of the life of the Universe, when the pressure was still very high. However, no trace of their existence has yet been discovered.

How to find a black hole

Just a few years ago, a light came on over black holes. Thanks to constantly improving instruments and technologies (both terrestrial and space), these objects are becoming less and less mysterious; more precisely, the space surrounding them becomes less mysterious. Indeed, since the black hole itself is invisible, we can only recognize it if it is surrounded by enough matter (stars and hot gas) orbiting it at a small distance.

Watching double systems

Some stellar black holes have been discovered by observing the orbital motion of a star around an invisible companion double system. Close binary systems (that is, consisting of two stars very close to each other), in which one of the companions is invisible, are a favorite object of observation for astrophysicists looking for black holes.

An indication of the presence of a black hole (or neutron star) is the strong emission of X-rays, caused by a complex mechanism, which can be schematically described as follows. Due to its powerful gravity, a black hole can rip matter out of a companion star; this gas is distributed in the form of a flat disk and falls in a spiral into the black hole. Friction resulting from collisions of particles of falling gas heats the inner layers of the disk to several million degrees, which causes powerful X-ray emission.

Observations in x-rays

Observations in X-rays of objects in our Galaxy and neighboring galaxies, which have been carried out for several decades, have made it possible to detect compact binary sources, about a dozen of which are systems containing black hole candidates. The main problem is to determine the mass of an invisible celestial body. The value of the mass (albeit not very accurate) can be found by studying the movement of the companion or, which is much more difficult, by measuring the intensity x-ray radiation falling substance. This intensity is connected by an equation with the mass of the body on which this substance falls.

Nobel Laureate

Something similar can be said about the supermassive black holes observed in the cores of many galaxies, whose masses are estimated by measuring the orbital velocities of the gas falling into the black hole. In this case, caused by a powerful gravitational field of a very large object, a rapid increase in the speed of gas clouds orbiting in the center of galaxies is revealed by observations in the radio range, as well as in optical beams. Observations in the X-ray range can confirm the increased release of energy caused by the fall of matter into the black hole. Research in X-rays in the early 1960s was started by the Italian Riccardo Giacconi, who worked in the USA. He was awarded the Nobel Prize in 2002 in recognition of his "groundbreaking contributions to astrophysics that led to the discovery of X-ray sources in space."

Cygnus X-1: the first candidate

Our Galaxy is not immune from the presence of black hole candidate objects. Fortunately, none of these objects are so close to us as to pose a danger to the existence of the Earth or solar system. In spite of a large number of noted compact X-ray sources (and these are the most likely candidates for finding black holes there), we are not sure that they actually contain black holes. The only one among these sources that does not have alternative version, is the close binary Cygnus X-1, that is, the brightest X-ray source, in the constellation Cygnus.

massive stars

This system, which has an orbital period of 5.6 days, consists of a very bright blue star big size(its diameter is 20 times greater than the sun, and its mass is about 30 times), easily distinguishable even in your telescope, and an invisible second star, the mass of which is estimated at several solar masses (up to 10). Located at a distance of 6500 light years from us, the second star would be perfectly visible if it were an ordinary star. Its invisibility, the system's powerful X-rays, and finally its mass estimate lead most astronomers to believe that this is the first confirmed discovery of a stellar black hole.

Doubts

However, there are also skeptics. Among them is one of the largest researchers of black holes, physicist Stephen Hawking. He even made a bet with his American colleague Keel Thorne, a strong supporter of the classification of Cygnus X-1 as a black hole.

The dispute over the nature of the Cygnus X-1 object is not Hawking's only bet. After devoting several nine years theoretical research black holes, he became convinced of the fallacy of his previous ideas about these mysterious objects. In particular, Hawking assumed that matter after falling into a black hole disappears forever, and with it all its informational baggage disappears. He was so sure of this that he made a bet on this subject in 1997 with his American colleague John Preskill.

Admitting a mistake

On July 21, 2004, in his speech at the Relativity Congress in Dublin, Hawking admitted that Preskill was right. Black holes don't lead to complete disappearance substances. Moreover, they have a certain kind of "memory". Inside them may well be stored traces of what they absorbed. Thus, by “evaporating” (that is, slowly emitting radiation due to the quantum effect), they can return this information to our Universe.

Black holes in the galaxy

Astronomers still have many doubts about the presence of stellar black holes in our Galaxy (like the one that belongs to the Cygnus X-1 binary system); but there is much less doubt about supermassive black holes.

In the center

There is at least one supermassive black hole in our galaxy. Its source, known as Sagittarius A*, is precisely located in the center of the plane of the Milky Way. Its name is explained by the fact that it is the most powerful radio source in the constellation Sagittarius. It is in this direction that both the geometric and physical centers of our galactic system are located. Located at a distance of about 26,000 light-years from us, a supermassive black hole associated with the source of radio waves, Sagittarius A *, has a mass that is estimated at about 4 million solar masses, contained in a space whose volume is comparable to the volume of the solar system. Its relative proximity to us (this supermassive black hole is without a doubt the closest to Earth) has caused the object to come under particularly deep scrutiny by the Chandra space observatory in recent years. It turned out, in particular, that it is also a powerful source of X-rays (but not as powerful as sources in active galactic nuclei). Sagittarius A* may be the dormant remnant of what was the active core of our Galaxy millions or billions of years ago.

Second black hole?

However, some astronomers believe that there is another surprise in our Galaxy. We are talking about a second black hole of average mass, holding together a cluster of young stars and not allowing them to fall into a supermassive black hole located in the center of the Galaxy itself. How can it be that at a distance of less than one light year from it there could be a star cluster with an age that has barely reached 10 million years, that is, by astronomical standards, very young? According to the researchers, the answer lies in the fact that the cluster was not born there (the environment around the central black hole is too hostile for star formation), but was “drawn” there due to the existence of a second black hole inside it, which has a mass of average values.

In orbit

The individual stars of the cluster, attracted by the supermassive black hole, began to shift towards the galactic center. However, instead of being dispersed into space, they remain together due to the attraction of a second black hole located at the center of the cluster. The mass of this black hole can be estimated from its ability to hold an entire star cluster "on a leash". A medium-sized black hole appears to revolve around the central black hole in about 100 years. This means that long-term observations over many years will allow us to "see" it.

Black holes are the only cosmic bodies capable of attracting light by gravity. They are also the largest objects in the universe. We're not likely to know what's going on near their event horizon (known as the "point of no return") anytime soon. These are the most mysterious places of our world, about which, despite decades of research, very little is known so far. This article contains 10 facts that can be called the most intriguing.

Black holes don't suck in matter.

Many people think of a black hole as a kind of "cosmic vacuum cleaner" that draws in the surrounding space. In fact, black holes are ordinary cosmic objects that have an exceptionally strong gravitational field.

If a black hole of the same size arose in the place of the Sun, the Earth would not be pulled inward, it would rotate in the same orbit as it does today. Stars located near black holes lose part of their mass in the form of stellar wind (this happens during the existence of any star) and black holes absorb only this matter.

The existence of black holes was predicted by Karl Schwarzschild

Karl Schwarzschild was the first to apply Einstein's general theory of relativity to justify the existence of a "point of no return". Einstein himself did not think about black holes, although his theory makes it possible to predict their existence.

Schwarzschild made his suggestion in 1915, just after Einstein published his general theory of relativity. That's when the term "Schwarzschild radius" came about, a value that tells you how much you have to compress an object to make it a black hole.

Theoretically, anything can become a black hole. enough compression. The denser the object, the stronger the gravitational field it creates. For example, the Earth would become a black hole if an object the size of a peanut had its mass.

Black holes can spawn new universes

The idea that black holes can spawn new universes seems absurd (especially since we are still not sure about the existence of other universes). Nevertheless, such theories are being actively developed by scientists.

A very simplified version of one of these theories is as follows. Our world has exceptionally favorable conditions for the emergence of life in it. If any of the physical constants changed even slightly, we would not be in this world. The singularity of black holes overrides the usual laws of physics and could (at least in theory) give rise to a new universe that would be different from ours.

Black holes can turn you (and anything) into spaghetti

Black holes stretch objects that are close to them. These objects begin to resemble spaghetti (there is even a special term - "spaghettiification").

This is due to the way gravity works. At the moment, your feet are closer to the center of the Earth than your head, so they are being pulled more strongly. At the surface of a black hole, the difference in gravity starts to work against you. The legs are attracted to the center of the black hole faster and faster, so that the upper half of the torso cannot keep up with them. Result: spaghettification!

Black holes evaporate over time

Black holes not only absorb the stellar wind, but also evaporate. This phenomenon was discovered in 1974 and was named Hawking radiation (after Stephen Hawking, who made the discovery).

Over time, the black hole can give all its mass into the surrounding space along with this radiation and disappear.

Black holes slow down time around them

As you get closer to the event horizon, time slows down. To understand why this happens, we need to turn to the “twin paradox”, thought experiment, often used to illustrate the fundamentals of Einstein's general theory of relativity.

One of the twin brothers remains on Earth, while the other flies off on a space journey, moving at the speed of light. Returning to Earth, the twin finds that his brother has aged more than he, because when moving at a speed close to the speed of light, time passes more slowly.

As you approach the event horizon of a black hole, you will be moving at such a high speed that time will slow down for you.

Black holes are the most advanced power plants

Black holes generate energy better than the Sun and other stars. This is due to the matter revolving around them. Overcoming the event horizon at great speed, the matter in the orbit of a black hole is heated to extremely high temperatures. This is called blackbody radiation.

For comparison, during nuclear fusion, 0.7% of matter is converted into energy. Near a black hole, 10% of matter becomes energy!

Black holes warp space around them

Space can be thought of as a stretched rubber band with lines drawn on it. If you put an object on the plate, it will change its shape. Black holes work the same way. Their extreme mass attracts everything to itself, including light (the rays of which, continuing the analogy, could be called lines on a plate).

Black holes limit the number of stars in the universe

Stars arise from gas clouds. In order for star formation to begin, the cloud must cool.

Radiation from black bodies prevents gas clouds from cooling and prevents the formation of stars.

Theoretically, any object can become a black hole.

The only difference between our Sun and a black hole is the strength of gravity. It is much stronger at the center of a black hole than at the center of a star. If our Sun were compressed to about five kilometers in diameter, it could be a black hole.

Theoretically, anything can become a black hole. In practice, we know that black holes arise only as a result of the collapse of huge stars, exceeding the mass of the Sun by 20-30 times.

S. TRANKOVSKY

Among the most important and interesting problems of modern physics and astrophysics, Academician V. L. Ginzburg named questions related to black holes (see Science and Life, Nos. 11, 12, 1999). The existence of these strange objects was predicted more than two hundred years ago, the conditions leading to their formation were accurately calculated in the late 30s of the XX century, and astrophysics came to grips with them less than forty years ago. Today scientific journals around the world publish thousands of articles on black holes every year.

The formation of a black hole can occur in three ways.

This is how it is customary to depict the processes taking place in the vicinity of a collapsing black hole. As time passes (Y), the space (X) around it (shaded area) shrinks towards the singularity.

The gravitational field of a black hole introduces strong distortions into the geometry of space.

A black hole, invisible through a telescope, reveals itself only by its gravitational influence.

In the powerful gravitational field of a black hole, particle-antiparticle pairs are born.

The birth of a particle-antiparticle pair in the laboratory.

HOW THEY APPEAR

A luminous celestial body, having a density equal to that of the Earth, and a diameter two hundred and fifty times greater than the diameter of the Sun, due to the force of its attraction, will not allow its light to reach us. Thus, it is possible that the largest luminous bodies in the universe, precisely because of their size, remain invisible.
Pierre Simon Laplace.
Presentation of the system of the world. 1796

In 1783, the English mathematician John Mitchell, and thirteen years later independently of him, the French astronomer and mathematician Pierre Simon Laplace conducted a very strange study. They considered the conditions under which light would not be able to leave a star.

The scientists' logic was simple. For any astronomical object (planet or star), you can calculate the so-called escape velocity, or the second cosmic velocity, which allows any body or particle to leave it forever. And in the physics of that time, the Newtonian theory reigned supreme, according to which light is a stream of particles (almost a hundred and fifty years remained before the theory of electromagnetic waves and quanta). The escape velocity of particles can be calculated based on the equality potential energy on the surface of the planet and kinetic energy a body that "ran away" for an infinitely long distance. This speed is determined by the formula #1#

where M is the mass of the space object, R is its radius, G is the gravitational constant.

From here, the radius of a body of a given mass is easily obtained (later called the "gravitational radius r g "), at which the escape velocity is equal to the speed of light:

This means that a star compressed into a sphere with radius r g< 2GM/c 2 will stop emitting - the light will not be able to leave it. A black hole will appear in the universe.

It is easy to calculate that the Sun (its mass is 2.1033 g) will turn into a black hole if it shrinks to a radius of about 3 kilometers. The density of its substance in this case will reach 10 16 g/cm 3 . The radius of the Earth, compressed to the state of a black hole, would decrease to about one centimeter.

It seemed incredible that forces could be found in nature that could compress a star to such an insignificant size. Therefore, the conclusions from the work of Mitchell and Laplace for more than a hundred years were considered something like a mathematical paradox that has no physical meaning.

Strict mathematical proof that such an exotic object in space is possible, was obtained only in 1916. The German astronomer Karl Schwarzschild, having analyzed the equations of the general theory of relativity of Albert Einstein, received an interesting result. Having studied the motion of a particle in the gravitational field of a massive body, he came to the conclusion that the equation loses physical meaning(its solution goes to infinity) at r= 0 and r = r g.

The points at which the characteristics of the field lose their meaning are called singular, that is, special. The singularity at the zero point reflects a point, or, what is the same, a centrally symmetric field structure (after all, any spherical body - a star or a planet - can be represented as a material point). And the points located on a spherical surface with a radius r g , form the very surface from which the escape velocity is equal to the speed of light. In the general theory of relativity, it is called the Schwarzschild singular sphere or the event horizon (why - it will become clear later).

Already on the example of objects familiar to us - the Earth and the Sun - it is clear that black holes are very strange objects. Even astronomers dealing with matter at extreme temperatures, density and pressure consider them to be very exotic, and until recently not everyone believed in their existence. However, the first indications of the possibility of the formation of black holes were already contained in A. Einstein's general theory of relativity, created in 1915. The English astronomer Arthur Eddington, one of the first interpreters and popularizers of the theory of relativity, in the 1930s derived a system of equations describing the internal structure of stars. It follows from them that the star is in equilibrium under the action of oppositely directed gravitational forces and internal pressure created by the motion of hot plasma particles inside the luminary and by the pressure of radiation generated in its depths. And this means that the star is a gas ball, in the center of which heat gradually decreasing towards the periphery. From the equations, in particular, it followed that the temperature of the Sun's surface is about 5500 degrees (which is quite consistent with the data of astronomical measurements), and in its center there should be about 10 million degrees. This allowed Eddington to make a prophetic conclusion: at such a temperature, a thermonuclear reaction is "ignited", sufficient to ensure the glow of the Sun. Atomic physicists of that time did not agree with this. It seemed to them that it was too "cold" in the bowels of the star: the temperature there was insufficient for the reaction to "go". To this the enraged theorist replied: "Look for a hotter place!"

And in the end, he turned out to be right: there really is a thermonuclear reaction in the center of the star (another thing is that the so-called "standard solar model", based on ideas about thermonuclear fusion, apparently turned out to be incorrect - see, for example, "Science and life" No. 2, 3, 2000). Nevertheless, the reaction in the center of the star takes place, the star shines, and the radiation that arises in this case keeps it in a stable state. But now the nuclear "fuel" in the star burns out. The release of energy stops, the radiation goes out, and the force holding back the gravitational attraction disappears. There is a limit on the mass of a star, after which the star begins to irreversibly shrink. Calculations show that this happens if the mass of the star exceeds two or three solar masses.

GRAVITATIONAL COLLAPSE

At first, the rate of contraction of the star is small, but its rate continuously increases, since the force of attraction is inversely proportional to the square of the distance. Compression becomes irreversible, there are no forces capable of counteracting self-gravity. This process is called gravitational collapse. The speed of the shell of the star towards its center increases, approaching the speed of light. And here the effects of the theory of relativity begin to play a role.

The escape velocity was calculated based on Newtonian ideas about the nature of light. From the point of view of general relativity, phenomena in the vicinity of a collapsing star occur somewhat differently. In its powerful gravitational field, the so-called gravitational redshift occurs. This means that the frequency of radiation coming from a massive object is shifted towards low frequencies. In the limit, at the boundary of the Schwarzschild sphere, the radiation frequency becomes zero. That is, an observer who is outside of it will not be able to find out anything about what is happening inside. That is why the Schwarzschild sphere is called the event horizon.

But reducing the frequency is tantamount to slowing down time, and when the frequency becomes zero, time stops. This means that an outside observer will see a very strange picture: the shell of a star falling with increasing acceleration, instead of reaching the speed of light, stops. From his point of view, the contraction will stop as soon as the size of the star approaches the gravitational radius
mustache. He will never see even one particle "diving" under the Schwarzschild sphere. But for a hypothetical observer falling into a black hole, everything will end in a matter of moments according to his watch. Thus, the gravitational collapse time of a star the size of the Sun will be 29 minutes, and a much denser and more compact neutron star - only 1/20,000 of a second. And here he is in trouble, connected with the geometry of space-time near a black hole.

The observer enters a curved space. Near the gravitational radius, the gravitational forces become infinitely large; they stretch the rocket with the astronaut-observer into an infinitely thin thread of infinite length. But he himself will not notice this: all his deformations will correspond to the distortions of space-time coordinates. These considerations, of course, refer to the ideal, hypothetical case. Any real body will be torn apart by tidal forces long before approaching the Schwarzschild sphere.

BLACK HOLES DIMENSIONS

The size of a black hole, or rather, the radius of the Schwarzschild sphere is proportional to the mass of the star. And since astrophysics does not impose any restrictions on the size of a star, a black hole can be arbitrarily large. If, for example, it arose during the collapse of a star with a mass of 10 8 solar masses (or due to the merger of hundreds of thousands, or even millions of relatively small stars), its radius would be about 300 million kilometers, twice the Earth's orbit. And the average density of the substance of such a giant is close to the density of water.

Apparently, it is precisely such black holes that are found in the centers of galaxies. In any case, astronomers today count about fifty galaxies, in the center of which, judging by indirect evidence (we will discuss them below), there are black holes with a mass of about a billion (10 9) solar ones. Apparently, our Galaxy also has its own black hole; its mass was estimated quite accurately - 2.4. 10 6 ±10% of the mass of the Sun.

The theory assumes that, along with such supergiants, black mini-holes with a mass of about 10 14 g and a radius of about 10 -12 cm (size atomic nucleus). They could appear in the first moments of the existence of the Universe as a manifestation of a very strong inhomogeneity of space-time with a colossal energy density. The conditions that existed then in the Universe are now realized by researchers at powerful colliders (accelerators on colliding beams). Experiments at CERN earlier this year yielded quark-gluon plasma, pre-existing matter. elementary particles. Research into this state of matter continues at Brookhaven, the American accelerator center. It is capable of accelerating particles to energies one and a half to two orders of magnitude higher than an accelerator in
CERN. The upcoming experiment caused serious anxiety: will a black mini-hole arise during its implementation, which will bend our space and destroy the Earth?

This fear caused such a strong response that the US government was forced to convene an authoritative commission to test this possibility. The commission, which consisted of prominent researchers, concluded that the energy of the accelerator is too low for a black hole to form (this experiment is described in the journal "Science and Life" No. 3, 2000).

HOW TO SEE THE INVISIBLE

Black holes emit nothing, not even light. However, astronomers have learned to see them, or rather, to find "candidates" for this role. There are three ways to detect a black hole.

1. It is necessary to follow the circulation of stars in clusters around a certain center of gravity. If it turns out that there is nothing in this center, and the stars revolve, as it were, around an empty place, we can say quite confidently: there is a black hole in this "emptiness". It was on this basis that the presence of a black hole in the center of our Galaxy was assumed and its mass was estimated.

2. A black hole actively sucks matter into itself from the surrounding space. Interstellar dust, gas, matter of nearby stars fall on it in a spiral, forming the so-called accretion disk, similar to the ring of Saturn. (This is exactly what was frightening in the Brookhaven experiment: a black mini-hole that arose in the accelerator will begin to suck the Earth into itself, and this process could not be stopped by any forces.) Approaching the Schwarzschild sphere, the particles experience acceleration and begin to radiate in the X-ray range. This radiation has a characteristic spectrum similar to the well-studied radiation of particles accelerated in a synchrotron. And if such radiation comes from some region of the Universe, we can say with certainty that there must be a black hole there.

3. When two black holes merge, gravitational radiation occurs. It is calculated that if the mass of each is about ten times the mass of the Sun, then when they merge in a matter of hours, energy equivalent to 1% of their total mass will be released in the form of gravitational waves. This is a thousand times more than the light, heat and other energy that the Sun has emitted over the entire period of its existence - five billion years. They hope to detect gravitational radiation with the help of gravitational-wave observatories LIGO and others, which are now being built in America and Europe with the participation of Russian researchers (see "Science and Life" No. 5, 2000).

And yet, although astronomers have no doubts about the existence of black holes, no one can categorically state that exactly one of them is located at a given point in space. Scientific ethics, the conscientiousness of the researcher require an unambiguous answer to the question posed, which does not tolerate discrepancies. It is not enough to estimate the mass of an invisible object, you need to measure its radius and show that it does not exceed the Schwarzschild one. And even within our Galaxy, this problem is not yet solved. That is why scientists show a certain restraint in reporting their discovery, and scientific journals are literally full of reports of theoretical work and observations of effects that can shed light on their mystery.

True, black holes also have one more property, predicted theoretically, which, perhaps, would make it possible to see them. But, however, under one condition: the mass of the black hole must be much less than the mass of the Sun.

A BLACK HOLE MAY BE "WHITE"

For a long time, black holes were considered the embodiment of darkness, objects that in a vacuum, in the absence of absorption of matter, do not radiate anything. However, in 1974, the famous English theorist Stephen Hawking showed that black holes can be assigned a temperature and therefore must radiate.

According to the concepts of quantum mechanics, vacuum is not a void, but a kind of "foam of space-time", a hodgepodge of virtual (unobservable in our world) particles. However, quantum energy fluctuations are capable of "thrown" a particle-antiparticle pair out of vacuum. For example, when two or three gamma quanta collide, an electron and a positron will appear as if from nothing. This and similar phenomena have been repeatedly observed in laboratories.

It is quantum fluctuations that determine the processes of radiation from black holes. If a pair of particles with energies E and -E(the total energy of the pair is zero), arises in the vicinity of the Schwarzschild sphere, further fate particles will be different. They can annihilate almost immediately or go under the event horizon together. In this case, the state of the black hole will not change. But if only one particle goes under the horizon, the observer will register another, and it will seem to him that it was generated by a black hole. In this case, a black hole that has absorbed a particle with energy -E, will reduce its energy, and with energy E- increase.

Hawking calculated the rates at which all these processes go, and came to the conclusion that the probability of absorption of particles with negative energy is higher. This means that the black hole loses energy and mass - it evaporates. In addition, it radiates as a completely black body with a temperature T = 6 . 10 -8 M With / M kelvin, where M c is the mass of the Sun (2.1033 g), M is the mass of the black hole. This simple relationship shows that the temperature of a black hole with a mass six times the Sun's is one hundred millionth of a degree. It is clear that such a cold body radiates practically nothing, and all the above arguments remain valid. Another thing - mini-holes. It is easy to see that with a mass of 10 14 -10 30 grams, they are heated to tens of thousands of degrees and are white hot! However, it should be immediately noted that there are no contradictions with the properties of black holes: this radiation is emitted by a layer above the Schwarzschild sphere, and not below it.

So, the black hole, which seemed to be forever frozen object, sooner or later disappears, evaporating. Moreover, as it "loses weight", the rate of evaporation increases, but it still takes an extremely long time. It is estimated that mini-holes weighing 10 14 grams, which appeared immediately after the Big Bang 10-15 billion years ago, should evaporate completely by our time. At the last stage of their life, their temperature reaches a colossal value, so the products of evaporation must be particles of extremely high energy. It is possible that they are the ones that generate wide atmospheric showers - EASs in the Earth's atmosphere. In any case, the origin of anomalously high-energy particles is another important and interesting problem, which may be closely related to no less exciting questions in black hole physics.