Publication date: 09/27/2012

Most people have a vague or incorrect idea of ​​what black holes are. Meanwhile, these are such global and powerful objects of the Universe, in comparison with which our Planet and all our life is nothing.

Essence

This is a space object that has such a huge gravity that it absorbs everything that falls within its limits. In fact, black hole is an object that does not even emit light and bends space-time. Even time flows more slowly near black holes.

In fact, the existence of black holes is only a theory (and a bit of practice). Scientists have assumptions and practical experience, but it has not yet been possible to study black holes closely. That is why black holes are conditionally called all objects that fit under given description. Black holes are little studied, and therefore a lot of questions remain unresolved.

Any black hole has an event horizon - that border, after which nothing can get out. Moreover, the closer an object is to a black hole, the slower it moves.

Education

There are several types and ways of formation of black holes:
- the formation of black holes as a result of the formation of the universe. Such black holes appeared immediately after the Big Bang.
- dying stars. When a star loses its energy and thermonuclear reactions stop, the star begins to shrink. Depending on the degree of compression, neutron stars, white dwarfs and, in fact, black holes are distinguished.
- obtaining by means of experiment. For example, in a collider, you can create a quantum black hole.

Versions

Many scientists are inclined to believe that black holes throw out all the absorbed matter elsewhere. Those. there must be "white holes" that operate on a different principle. If you can get into a black hole, but you can’t get out, then you can’t get into a white hole. The main argument of scientists is the sharp and powerful bursts of energy recorded in space.

String theorists generally created their own model of a black hole, which does not destroy information. Their theory is called "Fuzzball" - it allows you to answer questions related to the singularity and the disappearance of information.

What is singularity and disappearance of information? A singularity is a point in space characterized by infinite pressure and density. Many are confused by the fact of the singularity, because physicists cannot work with infinite numbers. Many are sure that there is a singularity in a black hole, but its properties are described very superficially.

If to speak plain language, then all problems and misunderstandings come out of the relation quantum mechanics and gravity. So far, scientists cannot create a theory that unites them. That is why there are problems with a black hole. After all, a black hole seems to destroy information, but the foundations of quantum mechanics are violated. Although quite recently, S. Hawking seemed to have resolved this issue, stating that information in black holes is still not destroyed.

stereotypes

First, black holes cannot exist indefinitely. And all thanks to the evaporation of Hawking. Therefore, one should not think that black holes will sooner or later swallow the Universe.

Secondly, our Sun will not become a black hole. Since the mass of our star will not be enough. Our sun is more likely to turn into a white dwarf (and that's not a fact).

Thirdly, the Large Hadron Collider will not destroy our Earth by creating a black hole. Even if they deliberately create a black hole and "release" it, because of its small size, it will absorb our planet for a very, very long time.

Fourth, don't think that a black hole is a "hole" in space. A black hole is a spherical object. Hence the majority of opinions that black holes lead to a parallel universe. However, this fact has not yet been proven.

Fifth, a black hole has no color. It is detected either X-rays, or against the background of other galaxies and stars (lens effect).

Due to the fact that people often confuse black holes with wormholes (which actually exist), among ordinary people these concepts do not differ. The wormhole really allows you to move in space and time, but so far only in theory.

Complex things in simple terms

It is difficult to describe such a phenomenon as a black hole in simple terms. If you consider yourself a techie who understands exact sciences, then I advise you to read the works of scientists directly. If you want to know more about this phenomenon, then read the writings of Stephen Hawking. He did a lot for science, and especially in the field of black holes. The evaporation of black holes is named after him. He is a supporter of the pedagogical approach, and therefore all his works will be understandable even to an ordinary person.

Books:
- Black Holes and Young Universes, 1993.
- World in a Nutshell 2001.
- « The shortest history Universe 2005" of the year.

I especially want to recommend his popular science films, which will tell you in an understandable language not only about black holes, but also about the Universe in general:
- "The Universe of Stephen Hawking" - a series of 6 episodes.
- "Deep into the Universe with Stephen Hawking" - a series of 3 episodes.
All these films have been translated into Russian and are often shown on Discovery channels.

Thank you for your attention!


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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, given 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 items begin to resemble spaghetti (there are even special term- "spaghettification").

This is due to the way gravity works. AT this moment your feet are closer to the center of the earth than your head, so they are more strongly attracted. 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, one must turn to the "twin paradox," a thought experiment often used to illustrate the basic tenets of Einstein's general theory of relativity.

One of the twin brothers remains on Earth, and the second flies to space trip 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 runs slower.

As you approach the event horizon of a black hole, you will move with such 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, at 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.

Mysterious and elusive black holes. The laws of physics confirm the possibility of their existence in the universe, but many questions still remain. Numerous observations show that holes exist in the universe and there are more than a million of these objects.

What are black holes?

Back in 1915, when solving Einstein's equations, such a phenomenon as "black holes" was predicted. However science community became interested in them only in 1967. They were then called "collapsed stars", "frozen stars".

Now a black hole is called a region of time and space that has such gravity that not even a ray of light can get out of it.

How are black holes formed?

There are several theories of the appearance of black holes, which are divided into hypothetical and realistic. The simplest and most widespread realistic theory is the theory of gravitational collapse of large stars.

When a sufficiently massive star before "death" grows in size and becomes unstable, consuming the last fuel. At the same time, the mass of the star remains unchanged, but its size decreases as the so-called compaction occurs. In other words, during compaction, a heavy nucleus "falls" into itself. In parallel with this, the compaction leads to a sharp increase in temperature inside the star and the outer layers of the celestial body are torn off, new stars are formed from them. At the same time, in the center of the star - the core falls into its own "center". As a result of the action of gravitational forces, the center collapses into a point - that is, the gravitational forces are so strong that they absorb the compacted core. This is how a black hole is born, which begins to distort space and time, so that even light cannot escape from it.

At the centers of all galaxies is a supermassive black hole. According to Einstein's theory of relativity:

"Any mass distorts space and time."

Now imagine how much a black hole distorts time and space, because its mass is huge and at the same time squeezed into an ultra-small volume. Because of this ability, the following oddity occurs:

“Black holes have the ability to practically stop time and compress space. Because of this strong distortion, the holes become invisible to us.”

If black holes are not visible, how do we know they exist?

Yes, even though a black hole is invisible, it should be noticeable due to the matter that falls into it. As well as stellar gas, which is attracted by a black hole, when approaching the event horizon, the temperature of the gas begins to rise to superhigh values, which leads to a glow. This is why black holes glow. Thanks to this, albeit a weak glow, astronomers and astrophysicists explain the presence in the center of the galaxy of an object with a small volume, but a huge mass. AT this moment As a result of observations, about 1000 objects have been discovered that are similar in behavior to black holes.

Black holes and galaxies

How can black holes affect galaxies? This question torments scientists all over the world. There is a hypothesis according to which it is the black holes located in the center of the galaxy that affect its shape and evolution. And that when two galaxies collide, black holes merge and during this process such great amount energy and matter that new stars form.

Types of black holes

  • According to existing theory, there are three types of black holes: stellar, supermassive, miniature. And each of them was formed in a special way.
  • - Black holes of stellar masses, it grows to enormous sizes and collapses.
    - Supermassive black holes, which can have a mass equivalent to millions of suns, are very likely to exist at the centers of almost all galaxies, including our own Milky Way. Scientists still have different hypotheses for the formation of supermassive black holes. So far, only one thing is known - supermassive black holes are a by-product of the formation of galaxies. Supermassive black holes - they differ from ordinary ones in that they have a very large size, but paradoxically low density.
  • - No one has yet been able to detect a miniature black hole that would have a mass less than the Sun. It is possible that miniature holes could have formed shortly after the "Big Bang", which is the initial exact existence of our universe (about 13.7 billion years ago).
  • - More recently, a new concept has been introduced as "white black holes". This is still a hypothetical black hole, which is the opposite of a black hole. Stephen Hawking actively studied the possibility of the existence of white holes.
  • - Quantum black holes - they exist so far only in theory. Quantum black holes can be formed when ultra-small particles collide as a result of a nuclear reaction.
  • - Primordial black holes are also a theory. They formed immediately after the occurrence.

There is currently a large number of open questions that remain to be answered by future generations. For example, can there really be so-called "wormholes" with which you can travel through space and time. What exactly happens inside a black hole and what laws these phenomena obey. And what about the disappearance of information in a black hole?

Black holes - perhaps the most mysterious and enigmatic astronomical objects in our Universe, have attracted attention since their discovery. pundits and excite the fantasy of science fiction writers. What are black holes and what do they look like? Black holes are extinguished stars, due to their physical features, which have such a high density and such powerful gravity that not even light can escape from them.

The history of the discovery of black holes

For the first time, the theoretical existence of black holes, long before their actual discovery, was suggested by someone D. Michel (an English priest from Yorkshire, who is fond of astronomy at his leisure) back in 1783. According to his calculations, if we take ours and compress it (in modern computer language, archive it) to a radius of 3 km, such a large (just huge) gravitational force is formed that even light cannot leave it. This is how the concept of a “black hole” appeared, although in fact it is not black at all, in our opinion, the term “dark hole” would be more appropriate, because it is precisely the absence of light that takes place.

Later, in 1918, the great scientist Albert Einstein wrote about the issue of black holes in the context of the theory of relativity. But only in 1967, through the efforts of the American astrophysicist John Wheeler, the concept of black holes finally won a place in academic circles.

Be that as it may, both D. Michel, and Albert Einstein, and John Wheeler in their works assumed only the theoretical existence of these mysterious celestial objects in outer space, however, the true discovery of black holes took place in 1971, when they were first seen through a telescope.

This is what a black hole looks like.

How do black holes form in space?

As we know from astrophysics, all stars (including our Sun) have some limited amount of fuel. And although the life of a star can last billions of light years, sooner or later this conditional supply of fuel comes to an end, and the star “goes out”. The process of "extinction" of a star is accompanied by intense reactions, during which the star undergoes a significant transformation and, depending on its size, can turn into a white dwarf, a neutron star, or a black hole. Moreover, the largest stars, which have incredibly impressive dimensions, usually turn into a black hole - due to the compression of these very incredible size there is a multiple increase in the mass and gravitational force of the newly formed black hole, which turns into a kind of galactic vacuum cleaner - absorbs everything and everything around it.

A black hole swallows a star.

A small note - our Sun, by galactic standards, is not at all a large star, and after fading, which will occur in about a few billion years, most likely it will not turn into a black hole.

But let's be honest with you - today, scientists still do not know all the intricacies of the formation of a black hole, undoubtedly, this is an extremely complex astrophysical process, which itself can last millions of light years. Although it is possible to advance in this direction, the detection and subsequent study of the so-called intermediate black holes, that is, stars that are in a state of extinction, in which the active process of forming a black hole is taking place, could. By the way, a similar star was discovered by astronomers in 2014 in the arm of a spiral galaxy.

How many black holes exist in the universe

According to the theories of modern scientists in our galaxy milky way There may be up to hundreds of millions of black holes. There can be no less of them in the galaxy next to us, to which there is nothing to fly from our Milky Way - 2.5 million light years.

Theory of black holes

Despite the huge mass (which is hundreds of thousands of times greater than the mass of our Sun) and the incredible strength of gravity, it was not easy to see black holes through a telescope, because they do not emit light at all. Scientists managed to notice a black hole only at the moment of its "meal" - the absorption of another star, at this moment a characteristic radiation appears, which can already be observed. Thus, the black hole theory has found actual confirmation.

Properties of black holes

The main property of a black hole is its incredible gravitational fields, which do not allow the surrounding space and time to remain in their own habitual state. Yes, you heard right, time inside a black hole flows many times slower than usual, and if you were there, then returning back (if you were so lucky, of course) you would be surprised to notice that centuries have passed on Earth, and you won’t even grow old have time. Although let's be truthful, if you were inside a black hole, you would hardly have survived, since the gravitational force there is such that any material object would simply be torn apart, not even into parts, into atoms.

But if you were even close to a black hole, within the limits of its gravitational field, then you would also have a hard time, because the more you resisted its gravity, trying to fly away, the faster you would fall into it. The reason for this seemingly paradox is the gravitational vortex field, which all black holes possess.

What if a person falls into a black hole

Evaporation of black holes

English astronomer S. Hawking discovered interesting fact: black holes also appear to give off evaporation. True, this applies only to holes of relatively small mass. The powerful gravity around them creates pairs of particles and antiparticles, one of the pair is pulled inward by the hole, and the second is ejected outward. Thus, a black hole radiates hard antiparticles and gamma rays. This evaporation or radiation from a black hole was named after the scientist who discovered it - "Hawking radiation".

The biggest black hole

According to the theory of black holes, in the center of almost all galaxies there are huge black holes with masses from several million to several billion solar masses. And relatively recently, scientists have discovered the two largest black holes known to date, they are in two nearby galaxies: NGC 3842 and NGC 4849.

NGC 3842 is the brightest galaxy in the constellation Leo, located at a distance of 320 million light-years from us. In the center of it there is a huge black hole with a mass of 9.7 billion solar masses.

NGC 4849 is a galaxy in the Coma cluster, 335 million light-years away, boasting an equally impressive black hole.

The zones of action of the gravitational field of these giant black holes, or in academic terms, their event horizon, is about 5 times the distance from the Sun to! Such a black hole would eat our solar system and wouldn't even flinch.

The smallest black hole

But there are very small representatives in the vast family of black holes. So the most dwarf black hole discovered by scientists at the moment in its mass is only 3 times the mass of our Sun. In fact, this is the theoretical minimum necessary for the formation of a black hole, if that star were a little smaller, the hole would not have formed.

Black holes are cannibals

Yes, there is such a phenomenon, as we wrote above, black holes are a kind of "galactic vacuum cleaners" that absorb everything around them, including ... other black holes. Recently, astronomers have discovered that a black hole from one galaxy is being eaten by another large black glutton from another galaxy.

  • According to the hypotheses of some scientists, black holes are not only galactic vacuum cleaners that suck everything into themselves, but under certain circumstances they themselves can generate new universes.
  • Black holes can evaporate over time. We wrote above that it was discovered by the English scientist Stephen Hawking that black holes have the property of radiation and after some very long period of time, when there is nothing to absorb around, the black hole will begin to evaporate more, until eventually it gives up all its mass into surrounding space. Although this is only an assumption, a hypothesis.
  • Black holes slow down time and bend space. We have already written about time dilation, but space in the conditions of a black hole will be completely curved.
  • Black holes limit the number of stars in the universe. Namely, their gravitational fields prevent the cooling of gas clouds in space, from which, as you know, new stars are born.

Black holes on the Discovery Channel, video

And in conclusion, we offer you an interesting scientific documentary about black holes from the Discovery channel.

S. TRANKOVSKY

Among the most important and interesting problems 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

luminous heavenly body, which has a density equal to that of the Earth, and a diameter two hundred and fifty times 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 speed, 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 (before the theory electromagnetic waves and there were still almost a hundred and fifty years left). The escape velocity of particles can be calculated on the basis of the equality of the potential energy on the surface of the planet and the kinetic energy of the body "escaping" to an infinitely large 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.

A rigorous 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 internal structure 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 surface temperature of the Sun 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: in the center of the star, a thermonuclear reaction really takes place (another matter 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" Nos. 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 equal to 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 signs (we will talk about 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 (the size of the atomic nucleus) should have arisen. 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 made it possible to obtain quark-gluon plasma - matter that existed before the appearance of 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 Nauka i Zhizn, 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, 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 solar masses, 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, she radiates as absolutely black body with temperature T = 6 . 10 -8 M with / M kelvins, 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 can be closely related to no less exciting questions in black hole physics.