Origin of the black hole. Black hole. What it is? The smallest black hole

A black hole is a region of space-time whose gravitational attraction is so strong that even objects moving at the speed of light, including quanta of light itself, cannot leave it. The boundary of this region is called the event horizon, and its characteristic size is called the gravitational radius.

The idea of ​​a “black hole” first appeared in 1916, when the physicist Schwarzschild was solving Einstein’s equations. Mathematics has led to the strange conclusion that there are compact objects around which an event horizon with interesting properties appears. But the term “black hole” did not yet exist. The event horizon is a region of space surrounding a black hole, once in which matter will never be able to leave this region and fall into the black hole. Light can still overcome the enormous force of gravity, send the last streams from the disappearing matter, but only for a short period of time, until the falling matter falls into the so-called singularity zone, for which it is no longer Karl Schwarzschild, a German astronomer, one of the founders of theoretical astrophysics

In the 1930s, Chadwick discovered the neutron. Soon, a hypothesis was put forward about the existence of neutrino stars, which, at large masses, turn out to be unstable and are compressed to a state of collapse. The term "black hole" still did not exist. It was only in the late 1960s that the American John Wheeler said “black hole.” This is a point in space where matter and energy disappear under the influence of gravitational forces. In this place, gravitational forces are so strong that everything nearby is literally sucked inside. Even light rays cannot escape from there, so the black hole is completely invisible. John Wheeler, American physicist.

A “black hole” can be detected by the specific X-ray radiation that is produced when it sucks in matter. In the 1970s, the American satellite "Uhuru" (in one of the African dialects - "Freedom") recorded specific x-ray radiation. Since then, the “black hole” has existed not only in calculations. It was for these studies that Riccardo Giacconi received the 2002 Nobel Prize. Riccardo Giacconi, American physicist of Italian origin, winner of the Nobel Prize in Physics in 2002 “for the creation of X-ray astronomy and the invention of the X-ray telescope”

At the moment, scientists have discovered about a thousand objects in the Universe that are classified as black holes. In total, scientists suggest, there are tens of millions of such objects. Currently, the only reliable way to distinguish a black hole from an object of another type is to measure the mass and size of the object and compare its radius with the gravitational radius, which is given by the formula =, where G is the gravitational constant, M is the mass of the object, c is Supermassive black holes speed of light. Overgrown very large black holes form the cores of most galaxies. These include the massive black hole at the core of our galaxy - Sagittarius A*, which is the closest supermassive black hole to the Sun. Currently, the existence of black holes of stellar and galactic scales is considered by most scientists to be reliably proven by astronomical observations. American astronomers have found that the masses of supermassive black holes may be significantly underestimated. Researchers have found that for stars to move in the way they are now observed in the M87 galaxy (which is located 50 million light-years from Earth), the mass of the central black hole must be as large as Radio Galaxy Picos A, an X-ray jet visible (blue) ) 300 thousand light years long, emanating from

Detection of supermassive black holes The most reliable evidence for the existence of supermassive black holes in the central regions of galaxies is considered to be the most reliable. Today, the resolution of telescopes is not sufficient to distinguish regions of space with a size on the order of the gravitational radius of a black hole. There are many ways to determine the mass and approximate dimensions of a supermassive body, but most of them are based on measuring the characteristics of the orbits of objects rotating around them (stars, radio sources, gas disks). In the simplest and fairly common case, rotation occurs along Keplerian orbits, as evidenced by the proportionality of the satellite's rotation speed to the square root of the semi-major axis of the orbit: . In this case, the mass of the central body is found according to the well-known formula.

There is sometimes a half-joking, sometimes serious debate between the French and the British: who should be considered the discoverer of the possibility of the existence of invisible stars - Frenchman P. Laplace or Englishman J. Michell? In 1973, the famous English theoretical physicists S. Hawking and G. Ellis, in a book devoted to modern special mathematical issues of the structure of space and time, cited the work of the Frenchman P. Laplace with proof of the possibility of the existence of black stars; At that time, the work of J. Michell was not yet known. In the fall of 1984, the famous English astrophysicist M. Rice, speaking at a conference in Toulouse, said that although it is not very convenient to say on the territory of France, he must emphasize that the Englishman J. Michell was the first to predict invisible stars, and showed a snapshot of the first page corresponding to his work. This historic remark was met with applause and smiles from those present.

How can one not recall the discussions between the French and the British about who predicted the position of the planet Neptune from disturbances in the movement of Uranus: the Frenchman W. Le Verrier or the Englishman J. Adams? As is known, both scientists independently correctly indicated the position new planet. Then the Frenchman W. Le Verrier was luckier. This is the fate of many discoveries. They are often done almost simultaneously and independently different people Usually priority is given to those who have penetrated deeper into the essence of the problem, but sometimes this is simply the whims of fortune.

But the prediction of P. Laplace and J. Michell was not yet a real prediction of a black hole. Why?

The fact is that in the time of P. Laplace it was not yet known that nothing in nature could move faster than light. It is impossible to outrun the light in emptiness! This was established by Einstein in the special theory of relativity already in our century. Therefore, for P. Laplace, the star he was considering was only black (non-luminous), and he could not know that such a star loses the ability to “communicate” with the outside world in any way, to “report” anything to distant worlds about the events taking place on it . In other words, he did not yet know that this was not only a “black”, but also a “hole” into which you could fall, but it was impossible to get out. Now we know that if light cannot come out of some region of space, then it means that nothing at all can come out, and we call such an object a black hole.

Another reason why P. Laplace’s reasoning cannot be considered rigorous is that he considered garvitation fields of enormous strength, in which falling bodies are accelerated to the speed of light, and the emerging light itself can be delayed, and applied the law of gravity Newton.

A. Einstein showed that Newton’s theory of gravitation is inapplicable for such fields, and created a new theory that is valid for superstrong fields, as well as for rapidly changing fields (for which Newton’s theory is also inapplicable!), etc. called it the general theory of relativity. It is the conclusions of this theory that should be used to prove the possibility of the existence of black holes and to study their properties.

General relativity is an amazing theory. She is so deep and slender that she evokes a feeling of aesthetic pleasure in everyone who gets to know her. Soviet physicists L. Landau and E. Lifshitz in their textbook “Field Theory” called it “the most beautiful of all existing physical theories.” German physicist Max Born said of the discovery of the theory of relativity: “I admire it as a work of art.” And the Soviet physicist V. Ginzburg wrote that it evokes “...a feeling... akin to that experienced when looking at the most outstanding masterpieces of painting, sculpture or architecture.”

Numerous attempts at popular presentation of Einstein's theory can, of course, give a general impression of it. But, frankly speaking, it is as little similar to the delight of knowing the theory itself as familiarity with a reproduction of the “Sistine Madonna” differs from the experience that arises when viewing the original created by the genius of Raphael.

And yet, when there is no opportunity to admire the original, you can (and should!) get acquainted with available reproductions, preferably good ones (and there are all kinds).

Novikov I.D.

History of black holes

Alexey Levin

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 1960-70s did people believe in their reality. However, the basic equation for the theory of black holes 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 its initial speed exceeds what is now called the second 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 a star that has consumed its nuclear fuel 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 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 it 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, 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 electrical charge. And all other characteristics of the predecessor star (structure, composition, spectral class, 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 the laws of 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 - a physical vacuum - is in fact 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 turns into a source of radiation and therefore loses energy and, consequently, 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 exactly 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 hypotheses, 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 should arise as a result of the atmosphere of an ordinary star being sucked away by the gravitational field of a 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 of the Milky Way, hidden by dust clouds, there is a hole with a mass of 3-4 million solar masses.

Stephen Hawking came to the conclusion that black holes of arbitrary mass could be born immediately after 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 time, set off cosmic fireworks in the form powerful flares 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 so 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 survive 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 will not be 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 that have a bunch of interesting properties. The results of the theoretical analysis of black hole radiation also led to a serious rethinking of the concept of entropy, which also deserves a separate discussion.

Space superflywheels

The static electrically neutral black holes we talked about are completely atypical of the real world. Collapsed stars typically rotate and may also have an electrical charge.

Baldness theorem

Giant holes in galactic nuclei are most likely formed from primary centers of gravitational condensation - a single “post-stellar” hole or several holes that merged as a result of collisions. Such seed holes swallow nearby stars and interstellar gas and thereby increase their mass many times over. The matter falling below the horizon again has both an electrical charge (cosmic gas and dust particles are easily ionized) and a rotational moment (the fall occurs with a twist, in a spiral). In any physical process the moment of inertia and charge are conserved, and therefore it is natural to assume that the formation of black holes is no exception.

But an even stronger statement is also true, a special case of which was formulated in the first part of the article (see A. Levin, The Amazing History of Black Holes, Popular Mechanics No. 11, 2005). Whatever the ancestors of a macroscopic black hole, it receives from them only mass, torque and electrical charge. According to John Wheeler, "a black hole has no hair." It would be more correct to say that no more than three “hairs” hang from the horizon of any hole, which was proven by the combined efforts of several theoretical physicists in the 1970s. True, a magnetic charge must also be preserved in the hole, the hypothetical carriers of which, magnetic monopoles, were predicted by Paul Dirac in 1931. However, these particles have not yet been discovered, and it is too early to talk about the fourth “hair”. In principle, there may be additional “hairs” associated with quantum fields, but in a macroscopic hole they are completely invisible.

And yet they spin

If a static star is recharged, the spacetime metric will change, but the event horizon will still remain spherical. However, for a number of reasons, stellar and galactic black holes cannot carry a large charge, so from the point of view of astrophysics this case is not very interesting. But the rotation of the hole entails more serious consequences. First, the shape of the horizon changes. Centrifugal forces compress it along the axis of rotation and stretch it in the equatorial plane, so that the sphere is transformed into something similar to an ellipsoid. In essence, the same thing happens with the horizon as with any rotating body, in particular with our planet - after all, the equatorial radius of the Earth is 21.5 km longer than the polar one. Secondly, rotation reduces the linear dimensions of the horizon. Recall that the horizon is the interface between events that may or may not send signals to distant worlds. If the hole's gravity captivates light quanta, then centrifugal forces, on the contrary, contribute to their escape into outer space. Therefore, the horizon of a rotating hole should be located closer to its center than the horizon of a static star with the same mass.

But that's not all. The hole in its rotation carries away the surrounding space. In the immediate vicinity of the hole, the entrainment is complete; at the periphery it gradually weakens. Therefore, the horizon of the hole is immersed in a special region of space - the ergosphere. The boundary of the ergosphere touches the horizon at the poles and moves farthest away from it in the equatorial plane. On this surface, the speed of space entrainment is equal to light speed; inside it it is greater than the speed of light, and outside it is less. Therefore any material body, be it a gas molecule, a particle of cosmic dust, or a reconnaissance probe, when it enters the ergosphere, it certainly begins to rotate around the hole, and in the same direction as itself.

Stellar Generators

The presence of an ergosphere, in principle, allows the hole to be used as a source of energy and. Let some object penetrate into the ergosphere and break up there into two fragments. It may turn out that one of them will fall under the horizon, and the other will leave the ergosphere, and its kinetic energy will exceed the initial energy of the whole body! The ergosphere also has the ability to amplify electromagnetic radiation that falls on it and is again scattered into space (this phenomenon is called superradiation).

However, the law of conservation of energy is unshakable - perpetual motion machines do not exist. When a hole feeds energy into particles or radiation, its own rotational energy decreases. The cosmic superflywheel gradually slows down, and in the end it may even stop. It is calculated that in this way up to 29% of the hole’s mass can be converted into energy. The only more effective process than this is the annihilation of matter and antimatter, since in this case the mass is completely converted into radiation. But solar thermonuclear fuel burns out with a much lower efficiency - about 0.6%.

Consequently, a rapidly rotating black hole is almost an ideal energy generator for cosmic supercivilizations (if, of course, such exist). In any case, nature has been using this resource since time immemorial. Quasars, the most powerful space “radio stations” (sources of electromagnetic waves), are powered by the energy of gigantic rotating holes located in the cores of galaxies. This hypothesis was put forward by Edwin Salpeter and Yakov Zeldovich back in 1964, and since then it has become generally accepted. The material approaching the hole forms a ring-shaped structure, the so-called accretion disk. Since the space near the hole is strongly twisted by its rotation, the inner zone of the disk is kept in the equatorial plane and slowly settles towards the event horizon. The gas in this zone is highly heated by internal friction and generates infrared, light, ultraviolet and x-ray radiation, and sometimes even gamma rays. Quasars also emit non-thermal radio emission, which is mainly due to the synchrotron effect.

Very shallow entropy

The bald hole theorem hides a very insidious pitfall. A collapsing star is a clump of superhot gas compressed by gravitational forces. The higher the density and temperature of stellar plasma, the less order and more chaos it contains. The degree of chaos is expressed by a very specific physical quantity - entropy. Over time, the entropy of any isolated object increases - this is the essence of the second law of thermodynamics. The entropy of the star before the collapse begins is prohibitively high, and the entropy of the hole seems to be extremely small, since only three parameters are needed to unambiguously describe the hole. Is the second law of thermodynamics violated during gravitational collapse?

Is it possible to assume that when a star turns into a supernova, its entropy is carried away along with the ejected shell? Unfortunately no. Firstly, the mass of the shell cannot be compared with the mass of the star, therefore the loss of entropy will be small. Secondly, it is not difficult to come up with an even more convincing mental “refutation” of the second law of thermodynamics. Let a body of non-zero temperature, possessing some kind of entropy, fall into the zone of attraction of a ready-made hole. Having fallen under the event horizon, it will disappear along with its entropy reserves, and the entropy of the hole, apparently, will not increase at all. It is tempting to argue that the alien's entropy does not disappear, but is transferred to the inside of the hole, but this is just a verbal trick. The laws of physics are fulfilled in the world accessible to us and our instruments, and the region below the event horizon for any external observer is terra incognita.

This paradox was resolved by Wheeler's graduate student Jacob Bekenstein. Thermodynamics has a very powerful intellectual resource - the theoretical study of ideal heat engines. Bekenstein came up with a mental device that transforms heat into useful work, using a black hole as a heater. Using this model, he calculated the entropy of a black hole, which turned out to be proportional to the area of ​​the event horizon. This area is proportional to the square of the hole's radius, which, recall, is proportional to its mass. When capturing any external object, the mass of the hole increases, the radius lengthens, the area of ​​the horizon increases and, accordingly, the entropy increases. Calculations have shown that the entropy of a hole that has swallowed an alien object exceeds the total entropy of this object and the hole before they met. Similarly, the entropy of a collapsing star is many orders of magnitude less than the entropy of the successor hole. In fact, from Bekenstein’s reasoning it follows that the surface of the hole has a non-zero temperature and therefore is simply obliged to emit thermal photons (and, if heated enough, other particles). However, Bekenstein did not dare to go that far (Stephen Hawking took this step).

What have we come to? Thinking about black holes not only leaves the second law of thermodynamics intact, but also allows us to enrich the concept of entropy. The entropy of an ordinary physical body is more or less proportional to its volume, and the entropy of a hole is proportional to the surface of the horizon. It can be strictly proven that it is greater than the entropy of any material object with the same linear dimensions. It means that maximum The entropy of a closed area of ​​space is determined solely by the area of ​​its outer boundary! As we see, a theoretical analysis of the properties of black holes allows us to draw very deep conclusions of a general physical nature.

Looking into the depths of the universe

How is the search for black holes in the depths of space carried out? Popular Mechanics asked this question to the famous astrophysicist and Harvard University professor Ramesh Narayan.

“The discovery of black holes should be considered one of the greatest achievements of modern astronomy and astrophysics. In recent decades, thousands of sources have been identified in space x-ray radiation, each of which consists of a normal star and a very small non-luminous object surrounded by an accretion disk. Dark bodies with masses ranging from one and a half to three solar masses are most likely neutron stars. However, among these invisible objects there are at least two dozen almost one hundred percent candidates for the role of a black hole. In addition, scientists have come to a consensus that at least two gigantic black holes are hidden in galactic nuclei. One of them is located in the center of our Galaxy; according to a publication last year by astronomers from the United States and Germany, its mass is 3.7 million solar masses (M s). Several years ago, my Harvard-Smithsonian Center for Astrophysics colleagues James Moran and Lincoln Greenhill made major contributions to weighing the hole at the center of the Seyfert galaxy NGC 4258, which pulled in at 35 million M s. In all likelihood, in the cores of many galaxies there are holes with a mass of from a million to several billion M s.

It is not yet possible to detect from Earth the truly unique signature of a black hole - the presence of an event horizon. However, we already know how to verify its absence. The radius of a neutron star is 10 kilometers; the same order of magnitude is the radius of the holes born as a result of stellar collapse. However, a neutron star has a solid surface, while a hole does not. The fall of matter onto the surface of a neutron star entails thermonuclear explosions, which generate periodic X-ray bursts lasting a second. And when the gas reaches the horizon of the black hole, it goes under it and does not manifest itself as any radiation. Therefore, the absence of short X-ray flashes is a powerful confirmation of the hole nature of the object. All two dozen binary systems supposedly containing black holes do not emit such flares.

It must be admitted that now we are forced to be content with negative evidence of the existence of black holes. The objects that we declare to be holes cannot be anything else from the point of view of generally accepted theoretical models. To put it differently, we consider them holes solely because we cannot reasonably consider them to be anything else. I hope that the next generations of astronomers will have a little better luck.”

To the words of Professor Narayan, we can add that astronomers have believed in the reality of the existence of black holes for quite some time. Historically, the first reliable candidate for this position was the dark satellite of the very bright blue supergiant HDE 226868, 6,500 light-years away. It was discovered in the early 1970s in the X-ray binary Cygnus X-1. According to the latest data, its mass is about 20 M s. It is worth noting that on September 20 of this year, data were published that almost completely dispelled doubts about the reality of another hole of galactic proportions, the existence of which astronomers first suspected 17 years ago. It is located in the center of the M31 galaxy, better known as the Andromeda Nebula. Galaxy M31 is very old, approximately 12 billion years old. The hole is also quite big - 140 million solar masses. By the fall of 2005, astronomers and astrophysicists were finally convinced of the existence of three supermassive black holes and a couple dozen more of their more modest companions.

Verdict of the theorists

Popular Mechanics also managed to talk with two of the most authoritative experts on the theory of gravity, who have devoted decades to research in the field of black holes. We asked them to list the most important achievements in this area. Here's what Caltech theoretical physics professor Kip Thorne told us:

“If we talk about macroscopic black holes, which are well described by the equations of general relativity, then in the field of their theory the main results were obtained back in the 60-80s of the 20th century. As for recent work, the most interesting of them made it possible to better understand the processes occurring inside a black hole as it ages. IN last years Considerable attention is paid to models of black holes in multidimensional spaces, which naturally appear in string theory. But these studies no longer relate to classical ones, but to quantum holes that have not yet been discovered. The main result of recent years is very convincing astrophysical confirmation of the reality of the existence of holes with a mass of several solar masses, as well as supermassive holes in the centers of galaxies. Today there is no longer any doubt that these holes really exist and that we well understand the processes of their formation.”

Valery Frolov, a student of Academician Markov and a professor at the University of the Canadian province of Alberta, answered the same question:

“First of all, I would name the discovery of a black hole in the center of our Galaxy. Theoretical studies of holes in spaces with additional dimensions are also very interesting, from which follows the possibility of the birth of miniholes in experiments at collider accelerators and in the processes of interaction of cosmic rays with terrestrial matter. Stephen Hawking recently sent out a preprint of a paper showing that the thermal radiation from a black hole is completely returned to external world information about the state of objects that have fallen under its horizon. Previously, he believed that this information was irreversibly disappearing, but now he came to the opposite conclusion. However, it must be emphasized that this problem can be finally solved only on the basis of the quantum theory of gravity, which has not yet been constructed.”

Hawking's work deserves a separate comment. From the general principles of quantum mechanics it follows that no information disappears without a trace, but only turns into a less “readable” form. However, black holes irreversibly destroy matter and, apparently, deal with information just as harshly. In 1976, Hawking published an article in which this conclusion was supported by mathematical apparatus. Some theorists agreed with him, some did not; in particular, string theorists believed that information was indestructible. Last summer, at a conference in Dublin, Hawking said that information is still preserved and leaves the surface of the evaporating hole along with thermal radiation. At this meeting, Hawking presented only a diagram of his new calculations, promising to publish them in full over time. And now, as Valery Frolov said, this work has become available in the form of a preprint.

Finally, we asked Professor Frolov to explain why he considers black holes one of the most fantastic inventions of human intelligence.

“Astronomers have long discovered objects that did not require significantly new physical ideas to understand. This applies not only to planets, stars and galaxies, but also to such exotic bodies as white dwarfs and neutron stars. But a black hole is something completely different, it is a breakthrough into the unknown. Someone said that its insides are the best place to place the underworld. The study of holes, especially singularities, simply forces the use of such non-standard concepts and models that until recently were practically not discussed in physics - for example, quantum gravity and string theory. Many problems arise here that are unusual for physics, even painful, but, as is now clear, absolutely real. Therefore, the study of holes constantly requires fundamentally new theoretical approaches, including those that are on the edge of our knowledge of the physical world.”

According to a recent statement by astronomers from Ohio University, the unusual double nucleus in the Andromeda galaxy is explained by a cluster of stars rotating in elliptical orbits around some massive object, most likely a black hole. These conclusions were made based on data obtained using the Hubble Space Telescope. Andromeda's binary core was first discovered in the 70s, but it wasn't until the mid-90s that the theory of black holes was put forward.

The idea that black holes exist in the cores of galaxies is not new.

There is even every reason to believe that the Milky Way - the galaxy to which the Earth belongs - has a large black hole in its core, the mass of which is 3 million times greater than the mass of the Sun. However, exploring the core of the Andromeda galaxy, which is located at a distance of 2 million light years, is easier than the core of our galaxy, to which light travels only 30 thousand years - you cannot see the forest for the trees.

Scientists simulate black hole collisions

Application of numerical simulation on supercomputers to clarify the nature and behavior of black holes, study of gravitational waves.

For the first time, scientists from the Institute of Gravitational Physics (Max-Planck-Institut fur Gravitationsphysik), also known as the Albert Einstein Institute and located in Golm, a suburb of Potsdam (Germany), simulated the merger of two black holes. The planned detection of gravitational waves emitted by two merging black holes requires full 3D simulations on supercomputers.

Black holes are so dense that they do not reflect or emit any light - which is why they are so difficult to detect. However, in a few years, scientists hope for a significant shift in this area.

Gravitational waves, which literally fill outer space, may be detected using new means at the beginning of the next century.

Scientists led by Professor Ed Seidel (Dr. Ed Seidel) are preparing numerical simulations for such studies, which will provide observers with a reliable way to detect the waves produced by black holes. “Collisions of black holes are one of the main sources of gravitational waves,” said Professor Seidel, who in recent years has conducted successful research in simulating gravitational waves that appear when black holes collapse in direct collisions.

However, the interaction of two spiraling black holes and their merger are more common than direct collisions and are of greater importance in astronomy. Such tangential collisions were first calculated by Bernd Brugman, working at the Albert Einstein Institute.

However, due to a lack of computing power at the time, he was unable to calculate crucial details such as the exact trace of the gravitational waves emitted, which contains important information about the behavior of black holes during a collision. Brugman published the latest results in the International Journal of Modern Physics.

In his first calculations, Brugman used the institute's Origin 2000 server. It includes 32 separate processors running in parallel with a total peak performance of 3 billion operations per second. And in June of this year, an international team consisting of Brugman, Seidel and other scientists was already working with a much more powerful 256-processor Origin 2000 supercomputer at the National Center for Supercomputing Applications (NCSA). The group also included scientists from

St. Louis University (USA) and from the Konrad-Zuse-Zentrum research center in Berlin. This supercomputer provided the first detailed simulation of tangential collisions of unequal-mass black holes, as well as their rotations, which Brugman had previously studied. Werner Benger from Konrad-Zuse-Zentrum even managed to reproduce a stunning picture of the collision process. It was demonstrated how “black monsters” with masses ranging from one to several hundred million solar masses merged, creating bursts of gravitational waves that could soon be detected by special means.

One of the most important results of this research work was the discovery of enormous energy emitted during the collision of black holes in the form of gravitational waves. If two objects with masses equivalent to 10 and 15 solar masses come within 30 miles of each other and collide, the amount of gravitational energy corresponds to 1% of their mass. "This is a thousand times more than all the energy released by our Sun over the past five billion years." - Brugman noted. Since most large collisions in the universe occur very far from earth, the signals should become very weak the moment they reach earth.

Construction of several high-precision detectors has begun around the world.

One of them, constructed by the Max Planck Institute as part of the German-British Geo 600 project, is a laser interferometer 0.7 miles long. Scientists hope to measure the short gravitational perturbations that occur during black hole collisions, but they expect only one such collision per year, and at a distance of about 600 million light years. Computer models are needed to provide observers with reliable information about detecting waves produced by black holes. Thanks to improvements in supercomputer simulation capabilities, scientists are on the verge of a new type of experimental physics.

Astronomers say they know the location of many thousands of black holes, but we are not able to do any experiments with them on earth. “Only in one case will we be able to study the details and construct a numerical model of them in our computers and observe it,” explained Professor Bernard Schutz, director of the Albert Einstein Institute. "I believe that the study of black holes will be a key research topic for astronomers in the first decade of the next century."

The companion star allows you to see the dust from the supernova.

Black holes cannot be seen directly, but astronomers can see evidence of their existence when gases spew onto a companion star.

If dynamite is detonated, tiny fragments of explosive will embed deeply into nearby objects, thus leaving permanent evidence of the explosion.

Astronomers have found a similar imprint on a star orbiting a black hole, not unreasonably believing that the black hole - a former star that collapsed so badly that not even light can overcome its gravitational pull - was created by a supernova explosion.

The light in the darkness.

By this time, astronomers had observed supernova explosions and discovered spotted objects in their place, which, in their opinion, were black holes. The new discovery is the first real evidence of a connection between one event and another. (Black holes cannot be seen directly, but their presence can sometimes be inferred by the effect of their gravitational field on nearby objects.

The star-and-black-hole system, designated GRO J1655-40, is located approximately 10,000 light-years away within our galaxy milky way. Discovered in 1994, it attracted the attention of astronomers with its strong flares. x-rays and a barrage of radio waves as the black hole pushed gases toward its companion star 7.4 million miles away.

Researchers from Spain and America began to take a closer look at the companion star, believing that it could retain some trace indicating the process of formation of a black hole.

Star-sized black holes are thought to be the bodies of large stars that simply shrunk to that size after using up all their hydrogen fuel. But for reasons still unclear, the dying star transforms into a supernova before exploding.

Observations by GRO J1655-40 in August and September 1994 showed that the ejected gas flowed at speeds up to 92% of the speed of light, providing partial evidence of the presence of a black hole.

Star dust.

If scientists are not mistaken, then some of the exploding stars, which were probably 25-40 times larger than our Sun, turned into surviving satellites.

This is exactly the data that astronomers discovered.

The companion star's atmosphere contained higher-than-normal concentrations of oxygen, magnesium, silicon and sulfur—heavy elements that can only be created in large quantities at the multibillion-degree temperatures reached during a supernova explosion. This was the first evidence that truly supported the theory that some black holes first appeared as supernovae, since what was seen could not have been born from the star that astronomers observed.

The concept of a black hole is known to everyone - from schoolchildren to the elderly; it is used in scientific and fantastic literature, in the tabloid media and at scientific conferences. But what exactly such holes are is not known to everyone.

From the history of black holes

1783 The first hypothesis of the existence of such a phenomenon as a black hole was put forward in 1783 by the English scientist John Michell. In his theory, he combined two of Newton's creations - optics and mechanics. Michell's idea was this: if light is a stream of tiny particles, then, like all other bodies, the particles should experience the attraction of a gravitational field. It turns out that the more massive the star, the more difficult it is for light to resist its attraction. 13 years after Michell, the French astronomer and mathematician Laplace put forward (most likely independently of his British colleague) a similar theory.

1915 However, all their works remained unclaimed until the beginning of the 20th century. In 1915, Albert Einstein published the General Theory of Relativity and showed that gravity is the curvature of spacetime caused by matter, and a few months later, German astronomer and theoretical physicist Karl Schwarzschild used it to solve a specific astronomical problem. He explored the structure of curved space-time around the Sun and rediscovered the phenomenon of black holes.

(John Wheeler coined the term "Black holes")

1967 American physicist John Wheeler outlined a space that can be crumpled, like a piece of paper, into an infinitesimal point and designated it with the term “Black Hole”.

1974 British physicist Stephen Hawking proved that black holes, although they absorb matter without return, can emit radiation and eventually evaporate. This phenomenon is called “Hawking radiation”.

2013 The latest research into pulsars and quasars, as well as the discovery of cosmic microwave background radiation, has finally made it possible to describe the very concept of black holes. In 2013, the gas cloud G2 came very close to the black hole and will most likely be absorbed by it, observing a unique process provides enormous opportunities for new discoveries of the features of black holes.

(The massive object Sagittarius A*, its mass is 4 million times greater than the Sun, which implies a cluster of stars and the formation of a black hole)

2017. A group of scientists from the multi-country collaboration Event Horizon Telescope, connecting eight telescopes from different points on the Earth’s continents, observed a black hole, which is a supermassive object located in the M87 galaxy, constellation Virgo. The mass of the object is 6.5 billion (!) solar masses, gigantic times greater than the massive object Sagittarius A*, for comparison, with a diameter slightly less than the distance from the Sun to Pluto.

Observations were carried out in several stages, starting in the spring of 2017 and throughout the periods of 2018. The volume of information amounted to petabytes, which then had to be decrypted and a genuine image of an ultra-distant object obtained. Therefore, it took another two whole years to thoroughly process all the data and combine them into one whole.

2019 The data was successfully decrypted and displayed, producing the first ever image of a black hole.

(The first ever image of a black hole in the M87 galaxy in the constellation Virgo)

The image resolution allows you to see the shadow of the point of no return in the center of the object. The image was obtained as a result of ultra-long baseline interferometric observations. These are so-called synchronous observations of one object from several radio telescopes interconnected by a network and located in different parts globe, directed in one direction.

What black holes actually are

A laconic explanation of the phenomenon goes like this.

A black hole is a space-time region whose gravitational attraction is so strong that no object, including light quanta, can leave it.

The black hole was once a massive star. As long as thermonuclear reactions maintain high pressure in its depths, everything remains normal. But over time, the energy supply is depleted and heavenly body, under the influence of its own gravity, begins to compress. The final stage of this process is the collapse of the stellar core and the formation of a black hole.

• 1. A black hole ejects a jet at high speed


• 2. A disk of matter grows into a black hole


• 3. Black hole


• 4. Detailed diagram of the black hole region


• 5. Size of new observations found

The most common theory is that similar phenomena exist in every galaxy, including the center of our Milky Way. The hole's enormous gravitational force is capable of holding several galaxies around it, preventing them from moving away from each other. The “coverage area” can be different, it all depends on the mass of the star that turned into a black hole, and can be thousands of light years.

Schwarzschild radius

The main property of a black hole is that any substance that falls into it can never return. The same applies to light. At their core, holes are bodies that completely absorb all light falling on them and do not emit any of their own. Such objects may visually appear as clots of absolute darkness.

• 1. Moving matter at half the speed of light


• 2. Photon ring


• 3. Inner photon ring


• 4. Event horizon in a black hole

Starting from General theory According to Einstein's relativity, if a body approaches a critical distance to the center of the hole, it will no longer be able to return. This distance is called the Schwarzschild radius. What exactly happens inside this radius is not known for certain, but there is the most common theory. It is believed that all the matter of a black hole is concentrated in an infinitesimal point, and at its center there is an object with infinite density, which scientists call a singular perturbation.

How does falling into a black hole happen?

(In the picture, the black hole Sagittarius A* looks like an extremely bright cluster of light)

Not so long ago, in 2011, scientists discovered a gas cloud, giving it the simple name G2, which emits unusual light. This glow may be due to friction in the gas and dust caused by the Sagittarius A* black hole, which orbits it as an accretion disk. Thus, we become observers of the amazing phenomenon of absorption of a gas cloud by a supermassive black hole.

According to recent studies, the closest approach to the black hole will occur in March 2014. We can recreate a picture of how this exciting spectacle will take place.

• 1. When first appearing in the data, a gas cloud resembles a huge ball of gas and dust.


• 2. Now, as of June 2013, the cloud is tens of billions of kilometers from the black hole. It falls into it at a speed of 2500 km/s.


• 3. The cloud is expected to pass by the black hole, but tidal forces caused by the difference in gravity acting on the leading and trailing edges of the cloud will cause it to take on an increasingly elongated shape.


• 4. After the cloud is torn apart, most of it will most likely flow into the accretion disk around Sagittarius A*, generating shock waves in it. The temperature will jump to several million degrees.


• 5. Part of the cloud will fall directly into the black hole. No one knows exactly what will happen to this substance next, but it is expected that as it falls it will emit powerful streams of X-rays and will never be seen again.

Video: black hole swallows a gas cloud

(Computer simulation of how much of the G2 gas cloud would be destroyed and consumed by the black hole Sagittarius A*)

What's inside a black hole

There is a theory that states that a black hole is practically empty inside, and all its mass is concentrated in an incredibly small point located at its very center - the singularity.

According to another theory, which has existed for half a century, everything that falls into a black hole passes into another universe located in the black hole itself. Now this theory is not the main one.

And there is a third, most modern and tenacious theory, according to which everything that falls into a black hole dissolves in the vibrations of strings on its surface, which is designated as the event horizon.

So what is an event horizon? It is impossible to look inside a black hole even with a super-powerful telescope, since even light, entering the giant cosmic funnel, has no chance of emerging back. Everything that can be at least somehow considered is located in its immediate vicinity.

The event horizon is a conventional surface line from under which nothing (neither gas, nor dust, nor stars, nor light) can escape. And this is the very mysterious point of no return in the black holes of the Universe.