Why do black holes form? Complex things in simple terms. What happens if you fall into a black hole

Have you ever seen a floor being vacuumed? If so, have you noticed how the vacuum cleaner sucks up dust and small debris like scraps of paper? Of course they noticed. Black holes do much the same thing as a vacuum cleaner, but instead of dust, they prefer to suck in larger objects: stars and planets. However, they will not disdain cosmic dust either.

How do black holes appear?

To understand where black holes come from, it would be nice to know what light pressure is. It turns out that light falling on objects puts pressure on them. For example, if we light a light bulb in a dark room, then an additional light pressure force will begin to act on all illuminated objects. This force is very small, and in Everyday life we, of course, will never be able to feel it. The reason is that a light bulb is a very weak light source. (In laboratory conditions, the light pressure of a light bulb can still be measured; Russian physicist P. N. Lebedev was the first to do this.) With stars, the situation is different. While the star is young and shining brightly, three forces are fighting inside it. On the one hand, the force of gravity, which tends to compress the star into a point, pulls the outer layers inward towards the core. On the other hand, there is the force of light pressure and the pressure force of hot gas, tending to inflate the star. The light produced in the star's core is so intense that it pushes away the outer layers of the star and balances the force of gravity pulling them toward the center. As a star ages, its core produces less and less light. This happens because during the life of a star, its entire supply of hydrogen burns out, we have already written about this. If the star is very large, 20 times heavier than the Sun, then its outer shells are very large in mass. Therefore, in a heavy star, the outer layers begin to move closer and closer to the core, and the entire star begins to contract. At the same time, the gravitational force on the surface of the contracting star increases. The more a star contracts, the more strongly it begins to attract the surrounding matter. Eventually, the star's gravity becomes so monstrously strong that even the light it emits cannot escape. At this moment the star becomes black hole. It no longer emits anything, but only absorbs everything that is nearby, including light. Not a single ray of light comes from it, so no one can see it, and that’s why it’s called a black hole: everything gets sucked in and never comes back.

What does a black hole look like?

If you and I were next to a black hole, we would see a fairly large luminous disk rotating around a small, completely black region of space. This black region is a black hole. And the luminous disk around it is matter falling into the black hole. Such a disk is called an accretion disk. The gravity of a black hole is very strong, so the matter sucked inside moves with very high acceleration and because of this it begins to radiate. By studying the light coming from such a disk, astronomers can learn a lot about the black hole itself. Another indirect sign of the existence of a black hole is the unusual movement of stars around a certain region of space. The hole's gravity forces nearby stars to move in elliptical orbits. Such movements of stars are also recorded by astronomers.
Now the attention of scientists is focused on the black hole located at the center of our galaxy. The fact is that a cloud of hydrogen with a mass about 3 times that of Earth is approaching the black hole. This cloud has already begun to change its shape due to the gravity of the black hole, in the coming years it will stretch even more and will be pulled inside the black hole.

We will never be able to see the processes occurring inside a black hole, so we can only be content with observing the disk around the black hole. But a lot of interesting things await us here too. Perhaps the most interesting phenomenon- the formation of ultra-fast jets of matter escaping from the center of this disk. The mechanism of this phenomenon remains to be elucidated, and it is quite possible that one of you will create a theory for the formation of such jets. For now, we can only register the X-ray flashes that accompany such “shots.”

This video shows how a black hole gradually captures material from a nearby star. In this case, an accretion disk is formed around the black hole, and part of its matter is ejected into space at enormous speeds. This generates a large number of X-ray radiation that is picked up by a satellite moving around the Earth.

How does a black hole work?

A black hole can be divided into three main parts. The outer part, being in which you can still avoid falling into a black hole if you move at very high speed. Deeper than the outer part there is an event horizon - this is an imaginary boundary, after crossing which the body loses all hope of returning from the black hole. Everything that is beyond the event horizon cannot be seen from the outside, because due to strong gravity, even light moving from inside will not be able to fly beyond it. It is believed that at the very center of a black hole there is a singularity - a region of space of a tiny volume in which a huge mass is concentrated - the heart of the black hole.

Is it possible to fly up to a black hole?

At a great distance, the attraction of a black hole is exactly the same as the attraction of an ordinary star with the same mass as the black hole. As you approach the event horizon, the attraction will grow stronger and stronger. Therefore, you can fly up to a black hole, but it is better to stay away from it so that you can return back. Astronomers had to watch how a black hole sucked a nearby star inside. You can see what it looked like in this video:

Will our Sun turn into a black hole?

No, it won't turn. The mass of the Sun is too small for this. Calculations show that in order to become a black hole, a star must be at least 4 times more massive than the Sun. Instead, the Sun will become a red giant and inflate to about the size of Earth's orbit before shedding its outer shell and becoming a white dwarf. We will definitely tell you more about the evolution of the Sun.

Despite the enormous achievements in the field of physics and astronomy, there are many phenomena whose essence is not fully revealed. Such phenomena include mysterious black holes, all information about which is only theoretical and cannot be verified in a practical way.

Do black holes exist?

Even before the advent of the theory of relativity, astronomers proposed a theory about the existence of black funnels. After the publication of Einstein's theory, the question of gravity was revised and new assumptions appeared in the problem of black holes. It is unrealistic to see this cosmic object, because it absorbs all the light entering its space. Scientists prove the existence of black holes based on analysis of the movement of interstellar gas and the trajectories of stars.

The formation of black holes leads to changes in space-time characteristics around them. Time seems to be compressed under the influence of enormous gravity and slows down. Stars that find themselves in the path of a black funnel can deviate from their route and even change direction. Black holes absorb the energy of their twin star, which also manifests itself.

What does a black hole look like?

Information regarding black holes is mostly hypothetical. Scientists study them for their effect on space and radiation. It is not possible to see black holes in the universe, because they absorb all the light that enters nearby space. An X-ray image of black objects was taken from special satellites, showing a bright center that is the source of the rays.

How are black holes formed?

A black hole in space is separate world, which has its own unique characteristics and properties. The properties of cosmic holes are determined by the reasons for their appearance. Regarding the appearance of black objects, there are the following theories:

1. They are the result of collapses occurring in space. This could be a collision of large cosmic bodies or a supernova explosion.
2. They arise due to the weighting of space objects while maintaining their size. The reason for this phenomenon has not been determined.

A black funnel is an object in space that is relatively small in size but has a huge mass. The black hole theory says that every cosmic object can potentially become a black funnel if, as a result of some phenomena, it loses its size but retains its mass. Scientists even talk about the existence of many black microholes - miniature space objects with a relatively large mass. This discrepancy between mass and size leads to an increase in the gravitational field and the appearance of strong attraction.

What's in a black hole?

The black mysterious object can only be called a hole with a big stretch. The center of this phenomenon is a cosmic body with increased gravity. The result of such gravity is a strong attraction to the surface of this cosmic body. In this case, a vortex flow is formed in which gases and grains of cosmic dust rotate. Therefore, it is more correct to call a black hole a black funnel.

It is impossible to find out in practice what is inside a black hole, because the level of gravity of the cosmic vortex does not allow any object to escape from its zone of influence. According to scientists, there is complete darkness inside a black hole, because light quanta disappear irrevocably inside it. It is assumed that space and time are distorted inside the black funnel; the laws of physics and geometry do not apply in this place. Such features of black holes can presumably lead to the formation of antimatter, which this moment unknown to scientists.

Why are black holes dangerous?

Black holes are sometimes described as objects that absorb surrounding objects, radiation and particles. This idea is incorrect: the properties of a black hole allow it to absorb only what falls within its zone of influence. It can absorb cosmic microparticles and radiation emanating from twin stars. Even if a planet is close to a black hole, it will not be absorbed, but will continue to move in its orbit.

What happens if you fall into a black hole?

The properties of black holes depend on the strength of the gravitational field. Black funnels attract everything that comes within their zone of influence. In this case, the spatiotemporal characteristics change. Scientists who study all things black holes disagree about what happens to the objects in this vortex:

• some scientists suggest that all objects falling into these holes are stretched or torn into pieces and do not have time to reach the surface of the attracting object;
• other scientists claim that in holes all the usual characteristics are distorted, so objects there seem to disappear in time and space. For this reason, black holes are sometimes called gateways to other worlds.

Types of black holes

Black funnels are divided into types based on the method of their formation:

1. Black objects of stellar mass are born at the end of the life of some stars. The complete combustion of a star and the end of thermonuclear reactions leads to the compression of the star. If the star undergoes gravitational collapse, it can transform into a black funnel.
2. Supermassive black funnels. Scientists claim that the core of any galaxy is a supermassive funnel, the formation of which is the beginning of the emergence of a new galaxy.
3. Primordial black holes. These may include holes of varying masses, including microholes formed due to discrepancies in the density of matter and the strength of gravity. Such holes are funnels formed at the beginning of the Universe. This also includes objects such as a hairy black hole. These holes are distinguished by the presence of rays similar to hairs. It is assumed that these photons and gravitons retain some of the information that falls into the black hole.
4. Quantum black holes. They appear as a result of nuclear reactions and live for a short time. Quantum funnels are of the greatest interest, since their study can help answer questions about the problem of black cosmic objects.
5. Some scientists identify this type of space object as a hairy black hole. These holes are distinguished by the presence of rays similar to hairs. It is assumed that these photons and gravitons retain some of the information that falls into the black hole.

Closest black hole to Earth

The nearest black hole is 3,000 light years away from Earth. It is called V616 Monocerotis, or V616 Mon. Its weight reaches 9-13 solar masses. This hole's binary partner is a star half the mass of the Sun. Another funnel relatively close to Earth is Cygnus X-1. It is located 6 thousand light years from Earth and weighs 15 times more than the Sun. This cosmic black hole also has its own binary partner, the movement of which helps to trace the influence of Cygnus X-1.

Black holes - interesting facts

Scientists tell the following interesting facts about black objects:

1. If we take into account that these objects are the center of galaxies, then to find the largest funnel, we must detect the largest galaxy. Therefore, the largest black hole in the universe is the funnel located in the galaxy IC 1101 at the center of the Abell 2029 cluster.
2. Black objects actually look like multi-colored objects. The reason for this lies in their radiomagnetic radiation.
3. There are no permanent physical or mathematical laws in the middle of a black hole. It all depends on the mass of the hole and its gravitational field.
4. The black funnels gradually evaporate.
5. The weight of black funnels can reach incredible sizes. The largest black hole has a mass equal to 30 million solar masses.

There is no cosmic phenomenon more mesmerizing in its beauty than black holes. As you know, the object got its name due to the fact that it is able to absorb light, but cannot reflect it. Due to their enormous gravity, black holes suck in everything that is near them - planets, stars, space debris. However, this is not all that you should know about black holes, since there are many amazing facts about them.

Black holes have no point of no return

For a long time It was believed that everything that falls into the region of a black hole remains in it, but the result of recent research is that after a while the black hole “spits out” all its contents into space, but in a different form, different from the original one. The event horizon, which was considered the point of no return for space objects, turned out to be only their temporary refuge, but this process occurs very slowly.

The Earth is threatened by a black hole

solar system just part of an infinite galaxy containing a huge number of black holes. It turns out that the Earth is threatened by two of them, but fortunately, they are located at a great distance - about 1600 light years. They were discovered in a galaxy that was formed as a result of the merger of two galaxies.


Scientists saw black holes only because they were near the solar system using an X-ray telescope, which is capable of capturing X-rays emitted by these space objects. Black holes, since they are located next to each other and practically merge into one, were called by one name - Chandra in honor of the Moon God from Hindu mythology. Scientists are confident that Chandra will soon become one due to the enormous force of gravity.

Black holes may disappear over time

Sooner or later, all the contents come out of the black hole and only radiation remains. As black holes lose mass, they become smaller over time and then disappear completely. The death of a space object is very slow and therefore it is unlikely that any scientist will be able to see how the black hole decreases and then disappears. Stephen Hawking argued that the hole in space is a highly compressed planet and over time it evaporates, starting at the edges of the distortion.

Black holes may not necessarily look black

Scientists claim that since a space object absorbs light particles without reflecting them, a black hole has no color, only its surface - the event horizon - gives it away. With its gravitational field, it obscures all space behind itself, including planets and stars. But at the same time, due to the absorption of planets and stars on the surface of a black hole in a spiral due to the enormous speed of movement of objects and friction between them, a glow appears, which can be brighter than the stars. This is a collection of gases, star dust and other matter that is sucked in by a black hole. Also, sometimes a black hole can emit electromagnetic waves and therefore can be visible.

Black holes are not created out of nowhere; they are based on an extinct star.

Stars glow in space thanks to their supply of thermonuclear fuel. When it ends, the star begins to cool, gradually turning from a white dwarf to a black dwarf. The pressure inside the cooled star begins to decrease. Under the influence of gravity, the cosmic body begins to shrink. The consequence of this process is that the star seems to explode, all its particles scatter in space, but at the same time the gravitational forces continue to act, attracting neighboring space objects, which are then absorbed by it, increasing the power of the black hole and its size.

Supermassive black hole

A black hole, tens of thousands of times larger than the size of the Sun, is located in the very center of the Milky Way. Scientists called it Sagittarius and it is located at a distance from the Earth 26,000 light years. This region of the galaxy is extremely active and is rapidly absorbing everything that is near it. She also often “spits out” extinct stars.


What is surprising is the fact that the average density of a black hole, even taking into account its huge size, may even be equal to the density of air. As the radius of the black hole increases, that is, the number of objects captured by it, the density of the black hole becomes less and this is explained simple laws physics. Thus, the most big bodies in space can actually be as light as air.

Black hole can create new universes

No matter how strange it may sound, especially given the fact that in fact black holes absorb and accordingly destroy everything around them, scientists are seriously thinking that these space objects could mark the beginning of the emergence of a new Universe. So, as we know, black holes not only absorb matter, but can also release it at certain periods. Any particle that comes out of a black hole can explode and this will become a new Big Bang, and according to his theory, our Universe appeared this way, therefore it is possible that the Solar system that exists today and in which the Earth revolves, populated by a huge number of people, was once born from a massive black hole.

Time passes very slowly near a black hole

When an object comes close to a black hole, no matter how much mass it has, its motion begins to slow down and this happens because in the black hole itself, time slows down and everything happens very slowly. This is due to the enormous gravitational force that the black hole has. Moreover, what happens in the black hole itself happens quite quickly, so if an observer were looking at the black hole from the outside, it would seem to him that all the processes occurring in it were proceeding slowly, but if he fell into its funnel, the gravitational forces would instantly tore it apart.

Scientific thinking sometimes constructs objects with such paradoxical properties that even the most insightful scientists initially refuse to recognize them. The most obvious example in history latest physics— a long-term lack of interest in black holes, extreme states of the gravitational field predicted almost 90 years ago. For a long time they were considered a purely theoretical abstraction, and only in the 1960s and 70s did people believe in their reality. However, the basic equation of black hole theory was derived over two hundred years ago.

John Michell's insight

The name of John Michell, physicist, astronomer and geologist, professor at Cambridge University and pastor of the Anglican Church, was completely undeservedly lost among the stars of English science of the 18th century. Michell laid the foundations of seismology - the science of earthquakes, carried out excellent research on magnetism and, long before Coulomb, invented the torsion balance, which he used for gravimetric measurements. In 1783, he tried to combine Newton's two great creations - mechanics and optics. Newton considered light to be a stream of tiny particles. Michell suggested that light corpuscles, like ordinary matter, obey the laws of mechanics. The consequence of this hypothesis turned out to be very non-trivial - celestial bodies can turn into traps for light.

How did Michell reason? A cannonball fired from the surface of a planet will completely overcome its gravity only if it starting speed will exceed the value now called the second escape velocity and escape velocity. If the planet's gravity is so strong that the escape velocity exceeds the speed of light, light corpuscles released at the zenith will not be able to go to infinity. The same will happen with reflected light. Consequently, the planet will be invisible to a very distant observer. Michell calculated the critical value of the radius of such a planet R cr depending on its mass M reduced to the mass of our Sun M s: R cr = 3 km x M/M s.

John Michell believed his formulas and assumed that the depths of space hide many stars that cannot be seen from Earth with any telescope. Later, the great French mathematician, astronomer and physicist Pierre Simon Laplace came to the same conclusion, who included it in both the first (1796) and second (1799) editions of his “Exposition of the World System”. But the third edition was published in 1808, when most physicists already considered light to be vibrations of the ether. The existence of “invisible” stars contradicted the wave theory of light, and Laplace considered it best simply not to mention them. In subsequent times, this idea was considered a curiosity, worthy of presentation only in works on the history of physics.

Schwarzschild model

In November 1915, Albert Einstein published a theory of gravity, which he called the general theory of relativity (GR). This work immediately found a grateful reader in the person of his colleague at the Berlin Academy of Sciences, Karl Schwarzschild. It was Schwarzschild who was the first in the world to use general relativity to solve a specific astrophysical problem, calculating the space-time metric outside and inside a non-rotating spherical body (for specificity, we will call it a star).

From Schwarzschild's calculations it follows that the gravity of a star does not distort the Newtonian structure of space and time too much only if its radius is much larger than the very value that John Michell calculated! This parameter was first called the Schwarzschild radius, and is now called the gravitational radius. According to general relativity, gravity does not affect the speed of light, but reduces the frequency of light vibrations in the same proportion as it slows down time. If the radius of a star is 4 times greater than the gravitational radius, then the flow of time on its surface slows down by 15%, and space acquires noticeable curvature. When exceeded twice, it bends more strongly, and time slows down by 41%. When the gravitational radius is reached, time on the surface of the star stops completely (all frequencies go to zero, the radiation freezes, and the star goes out), but the curvature of space there is still finite. Far from the star, the geometry still remains Euclidean, and time does not change its speed.

Despite the fact that the gravitational radius values ​​​​of Michell and Schwarzschild coincide, the models themselves have nothing in common. For Michell, space and time do not change, but light slows down. A star whose dimensions are smaller than its gravitational radius continues to shine, but it is visible only to a not too distant observer. For Schwarzschild, the speed of light is absolute, but the structure of space and time depends on gravity. A star that has fallen under the gravitational radius disappears for any observer, no matter where he is (more precisely, it can be detected by gravitational effects, but not by radiation).

From disbelief to affirmation

Schwarzschild and his contemporaries believed that such strange space objects did not exist in nature. Einstein himself not only adhered to this point of view, but also mistakenly believed that he had succeeded in substantiating his opinion mathematically.

In the 1930s, the young Indian astrophysicist Chandrasekhar proved that the nuclear fuel a star sheds its shell and turns into a slowly cooling white dwarf only if its mass is less than 1.4 solar masses. Soon the American Fritz Zwicky realized that supernova explosions produce extremely dense bodies of neutron matter; Later, Lev Landau came to the same conclusion. After Chandrasekhar’s work, it was obvious that only stars with a mass greater than 1.4 solar masses could undergo such an evolution. So a natural question arose: is there an upper limit to the mass of supernovae that neutron stars leave behind?

At the end of the 30s, the future father of the American atomic bomb, Robert Oppenheimer, established that such a limit actually exists and does not exceed several solar masses. It was not possible then to give a more accurate assessment; It is now known that the masses of neutron stars must be in the range of 1.5-3 M s. But even from the rough calculations of Oppenheimer and his graduate student George Volkow, it followed that the most massive descendants of supernovae do not become neutron stars, but transform into some other state. In 1939, Oppenheimer and Hartland Snyder used an idealized model to prove that a massive collapsing star is contracted to its gravitational radius. From their formulas it actually follows that the star does not stop there, but the co-authors refrained from such a radical conclusion.

The final answer was found in the second half of the 20th century through the efforts of a whole galaxy of brilliant theoretical physicists, including Soviet ones. It turned out that such a collapse Always compresses the star “all the way”, completely destroying its matter. As a result, a singularity arises, a “superconcentrate” of the gravitational field, closed in an infinitesimal volume. For a stationary hole this is a point, for a rotating hole it is a ring. The curvature of space-time and, therefore, the force of gravity near the singularity tends to infinity. At the end of 1967, American physicist John Archibald Wheeler was the first to call such a final stellar collapse a black hole. The new term was loved by physicists and delighted journalists, who spread it around the world (although the French did not like it at first, since the expression trou noir suggested dubious associations).

There, beyond the horizon

A black hole is neither matter nor radiation. With some figurativeness, we can say that this is a self-sustaining gravitational field concentrated in a highly curved region of space-time. Its outer boundary is defined by a closed surface, the event horizon. If the star did not rotate before the collapse, this surface turns out to be a regular sphere, the radius of which coincides with the Schwarzschild radius.

The physical meaning of the horizon is very clear. A light signal sent from its outer vicinity can travel an infinitely long distance. But signals sent from the inner region will not only not cross the horizon, but will inevitably “fall” into the singularity. The horizon is the spatial boundary between events that can become known to terrestrial (and any other) astronomers, and events about which information about which under no circumstances will come out.

As expected “according to Schwarzschild,” far from the horizon the attraction of a hole is inversely proportional to the square of the distance, so for a distant observer it manifests itself as an ordinary heavy body. In addition to mass, the hole inherits the moment of inertia of the collapsed star and its electric charge. And all other characteristics of the predecessor star (structure, composition, spectral type, etc.) fade into oblivion.

Let's send a probe to the hole with a radio station that sends a signal once a second according to onboard time. For a remote observer, as the probe approaches the horizon, the time intervals between signals will increase - in principle, unlimitedly. As soon as the ship crosses the invisible horizon, it will become completely silent for the “over-the-hole” world. However, this disappearance will not be without a trace, since the probe will give up its mass, charge and torque to the hole.

Black hole radiation

All previous models were built exclusively on the basis of general relativity. However, our world is governed by laws quantum mechanics, which do not ignore black holes. These laws do not allow us to consider the central singularity as a mathematical point. In a quantum context, its diameter is given by the Planck-Wheeler length, approximately equal to 10 -33 centimeters. In this area, ordinary space ceases to exist. It is generally accepted that the center of the hole is stuffed with various topological structures that appear and die in accordance with quantum probabilistic laws. The properties of such a bubbling quasi-space, which Wheeler called quantum foam, are still poorly understood.

The presence of a quantum singularity has a direct bearing on the fate of material bodies falling into the depths of a black hole. When approaching the center of the hole, any object made of currently known materials will be crushed and torn apart by tidal forces. However, even if future engineers and technologists create some super-strong alloys and composites with currently unprecedented properties, they are all still doomed to disappear: after all, in the singularity zone there is neither the usual time nor the usual space.

Now let's look at the horizon of the hole through a quantum mechanical lens. Empty space—the physical vacuum—is actually not empty at all. Due to quantum fluctuations of various fields in a vacuum, many virtual particles are continuously born and died. Since gravity near the horizon is very strong, its fluctuations create extremely strong gravitational bursts. When accelerated in such fields, newborn “virtuals” acquire additional energy and sometimes become normal long-lived particles.

Virtual particles are always born in pairs that move in opposite directions (this is required by the law of conservation of momentum). If a gravitational fluctuation extracts a pair of particles from the vacuum, it may happen that one of them materializes outside the horizon, and the second (the antiparticle of the first) inside. The “internal” particle will fall into the hole, but the “external” particle can escape under favorable conditions. As a result, the hole becomes a source of radiation and therefore loses energy and therefore mass. Therefore, black holes are not stable in principle.

This phenomenon is called the Hawking effect, after the remarkable English theoretical physicist who discovered it in the mid-1970s. Stephen Hawking, in particular, proved that the horizon of a black hole emits photons in the same way as an absolutely black body heated to a temperature of T = 0.5 x 10 -7 x M s /M. It follows that as the hole becomes thinner, its temperature increases, and “evaporation” naturally intensifies. This process is extremely slow, and the lifetime of a hole of mass M is about 10 65 x (M/M s) 3 years. When its size becomes equal to the Planck-Wheeler length, the hole loses stability and explodes, releasing the same energy as the simultaneous explosion of a million ten-megaton hydrogen bombs. Interestingly, the mass of the hole at the moment of its disappearance is still quite large, 22 micrograms. According to some models, the hole does not disappear without a trace, but leaves behind a stable relic of the same mass, the so-called maximon.

Maximon was born 40 years ago - as a term and as a physical idea. In 1965, Academician M.A. Markov suggested that there is an upper limit on the mass of elementary particles. He proposed to consider this limiting value as the dimension of mass, which can be combined from three fundamental physical constants - Planck's constant h, the speed of light C and the gravitational constant G (for those who like details: to do this you need to multiply h and C, divide the result by G and extract Square root). This is the same 22 micrograms that are mentioned in the article; this value is called the Planck mass. From the same constants one can construct a quantity with the dimension of length (the Planck-Wheeler length comes out to be 10 -33 cm) and with the dimension of time (10 -43 sec).
Markov went further in his reasoning. According to his hypothesis, the evaporation of a black hole leads to the formation of a “dry residue” - a maximon. Markov called such structures elementary black holes. To what extent this theory corresponds to reality is still an open question. In any case, analogues of Markov maximons have been revived in some models of black holes based on superstring theory.

Depths of space

Black holes are not prohibited by the laws of physics, but do they exist in nature? Absolutely rigorous evidence of the presence of at least one such object in space has not yet been found. However, it is very likely that in some binary systems the sources of X-ray emission are black holes of stellar origin. This radiation must arise due to atmospheric suction ordinary star gravitational field of the neighboring hole. As the gas moves toward the event horizon, it becomes very hot and emits X-ray quanta. At least two dozen X-ray sources are now considered suitable candidates for the role of black holes. Moreover, stellar statistics suggest that in our Galaxy alone there are about ten million holes of stellar origin.

Black holes can also form during the gravitational condensation of matter in galactic nuclei. This is how gigantic holes with a mass of millions and billions of solar masses arise, which, in all likelihood, exist in many galaxies. Apparently, in the center covered by dust clouds Milky Way hiding a hole with a mass of 3-4 million solar masses.

Stephen Hawking came to the conclusion that black holes of arbitrary mass could have been born immediately after the Big Bang, which gave rise to our Universe. Primary holes weighing up to a billion tons have already evaporated, but heavier ones can still hide in the depths of space and, in due course, set off cosmic fireworks in the form of powerful bursts of gamma radiation. However, such explosions have never been observed until now.

Black hole factory

Is it possible to accelerate particles in an accelerator to such a high energy that their collision creates a black hole? At first glance, this idea is simply crazy - the explosion of a hole will destroy all life on Earth. Moreover, it is technically infeasible. If the minimum mass of a hole is indeed 22 micrograms, then in energy units it is 10 28 electron volts. This threshold is 15 orders of magnitude higher than the capabilities of the world's most powerful accelerator, the Large Hadron Collider (LHC), which will be launched at CERN in 2007.

However, it is possible that the standard estimate of the hole's minimum mass is significantly overestimated. In any case, this is what physicists say, developing the theory of superstrings, which includes the quantum theory of gravity (though far from complete). According to this theory, space has not three dimensions, but at least nine. We don't notice the extra dimensions because they are looped on such a small scale that our instruments don't perceive them. However, gravity is omnipresent, it penetrates into hidden dimensions. In three-dimensional space, the force of gravity is inversely proportional to the square of the distance, and in nine-dimensional space it is proportional to the eighth power. Therefore, in a multidimensional world, the intensity of the gravitational field increases much faster as the distance decreases than in the three-dimensional world. In this case, the Planck length increases many times, and the minimum mass of the hole drops sharply.

String theory predicts that a black hole with a mass of only 10 -20 g can be born in nine-dimensional space. The calculated relativistic mass of protons accelerated in the Cern superaccelerator is approximately the same. According to the most optimistic scenario, it will be able to produce one hole every second, which will live for about 10 -26 seconds. In the process of its evaporation, all kinds of elementary particles will be born, which will not be difficult to register. The disappearance of the hole will lead to the release of energy, which is not enough even to heat one microgram of water by a thousandth of a degree. Therefore, there is hope that the LHC will turn into a factory of harmless black holes. If these models are correct, then new generation orbital cosmic ray detectors will be able to detect such holes.

All of the above applies to stationary black holes. Meanwhile, there are also rotating holes with a bouquet most interesting properties. results theoretical analysis black hole radiation also led to a serious rethinking of the concept of entropy, which also deserves a separate discussion. More on this in the next issue.

S. TRANKOVSKY

Among the most important and interesting problems of modern physics and astrophysics, Academician V.L. Ginzburg named issues related to black holes (see “Science and Life” No. 11, 12, 1999). The existence of these strange objects was predicted more than two hundred years ago, the conditions leading to their formation were precisely calculated in the late 30s of the 20th century, and astrophysics began to seriously study them less than forty years ago. Today scientific journals Every year thousands of articles on black holes are published around the world.

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

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

The gravitational field of a black hole introduces severe 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 ARISE

Luminous heavenly 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 gravity, will not allow its light to reach us. Thus, it is possible that the largest luminous bodies in the Universe remain invisible precisely because of their size.
Pierre Simon Laplace.
Exposition of the world system. 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 looked at the conditions under which light would be unable to escape the star.

The logic of the scientists was simple. For any astronomical object (planet or star), you can calculate the so-called escape velocity, or second escape velocity, allowing any body or particle to leave it forever. And in the physics of that time, Newton’s theory reigned supreme, according to which light is a flow of particles (the theory of electromagnetic waves and quanta was still almost a hundred and fifty years away). The escape velocity of particles can be calculated based on the equality of the potential energy on the surface of the planet and the kinetic energy of a body that has “escaped” to an infinitely large distance. This speed is determined by the formula #1#

Where M- mass of the space object, R- its radius, G- gravitational constant.

From this we can easily obtain the radius of a body of a given mass (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 a 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 contracts to a radius of approximately 3 kilometers. The density of its substance will reach 10 16 g/cm 3 . The radius of the Earth, compressed into a black hole, would decrease to about one centimeter.

It seemed incredible that there could be forces in nature capable of compressing a star to such an insignificant size. Therefore, the conclusions from the works of Mitchell and Laplace were considered for more than a hundred years to be something of a mathematical paradox that had no physical meaning.

Rigorous mathematical proof that such an exotic object in space was possible was obtained only in 1916. German astronomer Karl Schwarzschild, after analyzing the equations general theory Albert Einstein's relativity, got an interesting result. Having studied the motion of a particle in the gravitational field of a massive body, he came to the conclusion: the equation loses its physical meaning (its solution turns to infinity) when r= 0 and r = r g.

The points at which the characteristics of the field become meaningless are called singular, that is, special. The singularity at the zero point reflects the pointwise, or, what is the same thing, the centrally symmetric structure of the field (after all, any spherical body - a star or a planet - can be represented as a material point). And 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 will become clear later).

Already based 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 who deal with matter at extreme values ​​of temperature, density and pressure consider them 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 30s derived a system of equations describing internal structure stars It follows from them that the star is in equilibrium under the influence of oppositely directed gravitational forces and internal pressure created by the movement of hot plasma particles inside the star and the pressure of radiation generated in its depths. This means that the star is a gas ball, in the center of which there is a high temperature, gradually decreasing towards the periphery. From the equations, in particular, it followed that the surface temperature of the Sun was about 5500 degrees (which was quite consistent with the data of astronomical measurements), and in its center it should be about 10 million degrees. This allowed Eddington to make a prophetic conclusion: at this temperature, a thermonuclear reaction “ignites”, 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 depths of the star: the temperature there was not enough 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: a thermonuclear reaction really takes place 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). But nevertheless, the reaction in the center of the star takes place, the star shines, and the radiation that arises keeps it in a stable state. But the nuclear “fuel” in the star burns out. The release of energy stops, the radiation goes out, and the force restraining gravitational attraction disappears. There is a limit on the mass of a star, after which the star begins to shrink irreversibly. Calculations show that this happens if the mass of the star exceeds two to 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 gravity is inversely proportional to the square of the distance. The compression becomes irreversible; there are no forces capable of counteracting self-gravity. This process is called gravitational collapse. The speed of movement of the star's shell 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, a so-called gravitational redshift occurs. This means that the frequency of radiation coming from a massive object is shifted towards lower frequencies. In the limit, at the boundary of the Schwarzschild sphere, the radiation frequency becomes zero. That is, an observer located 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 decreasing the frequency equals 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, stops instead of reaching the speed of light. From his point of view, the compression will stop as soon as the size of the star approaches gravitational
usu. He will never see even one particle “dive” under the Schwarzschiel sphere. But for a hypothetical observer falling into a black hole, everything will be over in a matter of moments on his watch. Thus, the time of gravitational collapse 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 faces trouble associated with the geometry of space-time near a black hole.

The observer finds himself in a curved space. Near the gravitational radius, 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 an ideal, hypothetical case. Any real body will be torn apart by tidal forces long before approaching the Schwarzschild sphere.

DIMENSIONS OF BLACK HOLES

The size of a black hole, or more precisely, 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 will 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, these are the kind of 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 (discussed below), there are black holes with a mass of about a billion (10 9) solar. Our Galaxy also apparently has its own black hole; Its mass was estimated quite accurately - 2.4. 10 6 ±10% of the mass of the Sun.

The theory suggests 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 an atomic nucleus) should also appear. They could appear in the first moments of the existence of the Universe as a manifestation of very strong inhomogeneity of space-time with colossal energy density. Today, researchers realize the conditions that existed in the Universe at that time at powerful colliders (accelerators using colliding beams). Experiments at CERN earlier this year produced quark-gluon plasma, matter that existed before the emergence 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 the accelerator in
CERN. The upcoming experiment has caused serious concern: will it create a mini-black hole that will bend our space and destroy the Earth?

This fear resonated so strongly that the US government was forced to convene an authoritative commission to examine this possibility. A commission consisting of prominent researchers concluded: the energy of the accelerator is too low for a black hole to arise (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 monitor the rotation of stars in clusters around a certain center of gravity. If it turns out that there is nothing in this center, and the stars seem to be spinning around an empty space, we can say quite confidently: in this “emptiness” there is a black hole. 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, and matter from nearby stars fall onto it in a spiral, forming a so-called accretion disk, similar to the ring of Saturn. (This is precisely the scarecrow in the Brookhaven experiment: a mini-black hole that appeared in the accelerator will begin to suck the Earth into itself, and this process could not be stopped by any force.) Approaching the Schwarzschild sphere, the particles experience acceleration and begin to emit 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 confidence 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 in the form gravitational waves energy equivalent to 1% of their total mass will be released. This is a thousand times more than the light, heat and other energy that the Sun emitted during its entire 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 dares to categorically assert that exactly one of them is located at a given point in space. Scientific ethics and the integrity of the researcher require an unambiguous answer to the question posed, one that 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 radius. And even within our Galaxy this problem is not yet solvable. That is why scientists show a certain restraint in reporting their discovery, and scientific journals are literally filled with reports of theoretical work and observations of effects that can shed light on their mystery.

However, black holes have one more property, theoretically predicted, which might make it possible to see them. But, however, under one condition: the mass of the black hole should be much less than the mass of the Sun.

A BLACK HOLE CAN ALSO 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, emit nothing. However, in 1974, the famous English theorist Stephen Hawking showed that black holes can be assigned a temperature, and therefore should radiate.

According to the concepts of quantum mechanics, vacuum is not emptiness, but a kind of “foam of space-time,” a mishmash of virtual (unobservable in our world) particles. However, quantum energy fluctuations can “eject” a particle-antiparticle pair from the vacuum. For example, in the collision of two or three gamma quanta, an electron and a positron will appear as if out of thin air. This and similar phenomena have been repeatedly observed in laboratories.

It is quantum fluctuations that determine the radiation processes of black holes. If a pair of particles with energies E And -E(the total energy of the pair is zero), appears 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 below the horizon, the observer will register another, and it will seem to him that it was generated by a black hole. At the same time, a black hole that absorbed a particle with energy -E, will reduce your energy, and with energy E- will increase.

Hawking calculated the rates at which all these processes occur and came to the conclusion: 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 kelvins, where M c - mass of the Sun (2.10 33 g), M- the mass of the black hole. This simple relationship shows that the temperature of a black hole with a mass six times that of the sun is equal to one hundred millionth of a degree. It is clear that such a cold body emits practically nothing, and all the above reasoning remains valid. Mini-holes are another matter. 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 white-hot! It should be noted right away, however, 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 an eternally frozen object, sooner or later disappears, evaporating. Moreover, as she “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. On last stage During their lifetime, their temperature reaches colossal values, so the products of evaporation must be particles of extremely high energy. Perhaps they are the ones that generate widespread air showers in the Earth's atmosphere - EAS. In any case, the origin of particles of anomalously high energy is another important and interesting problem that can be closely related to no less exciting questions in the physics of black holes.