« Science fiction can be useful - it stimulates the imagination and eliminates fear of the future. However scientific facts may turn out to be much more amazing. Science fiction never even imagined the existence of such things as black holes»
Stephen Hawking
In the depths of the universe there are countless mysteries and secrets hidden for humans. One of them is black holes - objects that even people cannot understand. greatest minds humanity. Hundreds of astrophysicists are trying to uncover the nature of black holes, but at this stage we have not even proven their existence in practice.
Film directors dedicate their films to them, and among ordinary people black holes have become such a cult phenomenon that they are identified with the end of the world and inevitable death. They are feared and hated, but at the same time they are idolized and worshiped by the unknown that these strange fragments of the Universe conceal within themselves. Agree, being swallowed up by a black hole is such a romantic thing. With their help, it is possible, and they can also become guides for us in.
The yellow press often speculates on the popularity of black holes. Finding headlines in newspapers related to the end of the world due to another collision with a supermassive black hole is not a problem. Much worse is that the illiterate part of the population takes everything seriously and raises a real panic. To bring some clarity, we will take a journey to the origins of the discovery of black holes and try to understand what they are and how to approach them.
Invisible stars
It so happened that modern physicists describe the structure of our Universe using the theory of relativity, which Einstein carefully provided to humanity at the beginning of the 20th century. Black holes become even more mysterious, at the event horizon of which all the laws of physics known to us, including Einstein’s theory, cease to apply. Isn't this wonderful? In addition, the conjecture about the existence of black holes was expressed long before Einstein himself was born.
In 1783 there was a significant increase in scientific activity in England. In those days, science went side by side with religion, they got along well together, and scientists were no longer considered heretics. Moreover, priests were engaged in scientific research. One of these servants of God was the English pastor John Michell, who wondered not only about questions of existence, but also completely scientific tasks. Michell was a very titled scientist: initially he was a teacher of mathematics and ancient linguistics at one of the colleges, and after that he was accepted into the Royal Society of London for a number of discoveries.
John Michell studied seismology, but in his spare time he liked to think about the eternal and the cosmos. So he came up with the idea that somewhere in the depths of the Universe there could be supermassive bodies with such powerful gravity that in order to overcome the gravitational force of such a body it is necessary to move at a speed equal to or higher than the speed of light. If we accept such a theory as true, then even light will not be able to develop a second escape velocity (the speed necessary to overcome the gravitational attraction of the leaving body), so such a body will remain invisible to the naked eye.
Michell called his new theory “dark stars,” and at the same time tried to calculate the mass of such objects. He expressed his thoughts on this matter in open letter London royal society. Unfortunately, in those days such research was not of particular value for science, so Michell’s letter was sent to the archives. Only two hundred years later, in the second half of the 20th century, it was discovered among thousands of other records carefully stored in the ancient library.
The first scientific evidence for the existence of black holes
After Einstein's General Theory of Relativity was published, mathematicians and physicists seriously began solving the equations presented by the German scientist, which were supposed to tell us a lot of new things about the structure of the Universe. The German astronomer and physicist Karl Schwarzschild decided to do the same thing in 1916.
The scientist, using his calculations, came to the conclusion that the existence of black holes is possible. He was also the first to describe what was later called the romantic phrase "event horizon" - the imaginary boundary of space-time at a black hole, after crossing which there is a point of no return. Nothing will escape from the event horizon, not even light. It is beyond the event horizon that the so-called “singularity” occurs, where the laws of physics known to us cease to apply.
Continuing to develop his theory and solving equations, Schwarzschild discovered new secrets of black holes for himself and the world. Thus, he was able, solely on paper, to calculate the distance from the center of the black hole, where its mass is concentrated, to the event horizon. This distance Schwarzschild called it the gravitational radius.
Despite the fact that mathematically, Schwarzschild's solutions were extremely correct and could not be refuted, the scientific community of the early 20th century could not immediately accept such a shocking discovery, and the existence of black holes was written off as a fantasy, which appeared every now and then in the theory of relativity. For the next decade and a half, space exploration for the presence of black holes was slow, and only a few adherents of the German physicist’s theory were engaged in it.
Stars giving birth to darkness
After Einstein's equations were sorted into pieces, it was time to use the conclusions drawn to understand the structure of the Universe. In particular, in the theory of stellar evolution. It's no secret that in our world nothing lasts forever. Even stars have their own life cycle, albeit longer than a person.
One of the first scientists to become seriously interested in stellar evolution was the young astrophysicist Subramanyan Chandrasekhar, a native of India. In 1930 he released scientific work, which described the supposed internal structure stars, as well as their life cycles.
Already at the beginning of the 20th century, scientists guessed about such a phenomenon as gravitational compression(gravitational collapse). At a certain point in its life, the star begins to shrink at tremendous speed under the influence of gravitational forces. As a rule, this happens at the moment of the death of a star, but during gravitational collapse there are several ways for the continued existence of a hot ball.
Chandrasekhar's thesis advisor Ralph Fowler, a respected theoretical physicist in his day, suggested that during gravitational collapse any star turns into a smaller and hotter one - a white dwarf. But it turned out that the student “broke” the teacher’s theory, which was shared by most physicists at the beginning of the last century. According to the work of a young Indian, the demise of a star depends on its initial mass. For example, only those stars whose mass does not exceed 1.44 times the mass of the Sun can become white dwarfs. This number was called the Chandrasekhar limit. If the mass of the star exceeded this limit, then it dies in a completely different way. Under certain conditions, such a star at the moment of death can be reborn into a new, neutron star - another mystery modern universe. The theory of relativity tells us another option - compression of the star to ultra-small values, and this is where the fun begins.
In 1932, an article appeared in one of the scientific journals in which genius physicist from the USSR Lev Landau suggested that during collapse a supermassive star is compressed into a point with an infinitesimal radius and infinite mass. Despite the fact that such an event is very difficult to imagine from the point of view of an unprepared person, Landau was not far from the truth. The physicist also suggested that, according to the theory of relativity, gravity at such a point will be so great that it will begin to distort space-time.
Astrophysicists liked Landau's theory, and they continued to develop it. In 1939, in America, thanks to the efforts of two physicists - Robert Oppenheimer and Hartland Snyder - a theory emerged that described in detail a supermassive star at the time of collapse. As a result of such an event, a real black hole should have appeared. Despite the convincing arguments, scientists continued to deny the possibility of the existence similar bodies, as well as the transformation of stars into them. Even Einstein distanced himself from this idea, believing that a star was not capable of such phenomenal transformations. Other physicists did not skimp on their statements, calling the possibility of such events absurd.
However, science always reaches the truth, you just have to wait a little. And so it happened.
The brightest objects in the Universe
Our world is a collection of paradoxes. Sometimes things coexist in it, the coexistence of which defies any logic. For example, the term “black hole” would not be associated by a normal person with the expression “incredibly bright,” but a discovery in the early 60s of the last century allowed scientists to consider this statement to be incorrect.
With the help of telescopes, astrophysicists were able to discover hitherto unknown objects in the starry sky, which behaved very strangely despite the fact that they looked like ordinary stars. While studying these strange luminaries, the American scientist Martin Schmidt drew attention to their spectrography, the data of which showed results different from scanning other stars. Simply put, these stars were not like others we are used to.
Suddenly it dawned on Schmidt, and he noticed a shift in the spectrum in the red range. It turned out that these objects are much further from us than the stars that we are used to observing in the sky. For example, the object observed by Schmidt was located two and a half billion light years from our planet, but shone as brightly as a star some hundred light years away. It turns out that the light from one such object is comparable to the brightness of an entire galaxy. This discovery was a real breakthrough in astrophysics. The scientist called these objects “quasi-stellar” or simply “quasar”.
Martin Schmidt continued to study new objects and found that such a bright glow can only be caused by one reason - accretion. Accretion is the process of absorption of surrounding matter by a supermassive body using gravity. The scientist came to the conclusion that at the center of quasars there is a huge black hole, which incredible strength draws into itself the matter surrounding it in space. As matter is absorbed by the hole, the particles accelerate to enormous speeds and begin to glow. A kind of luminous dome around a black hole is called an accretion disk. Its visualization was well demonstrated in Christopher Nolan's film Interstellar, which gave rise to many questions: “how can a black hole glow?”
To date, scientists have already found thousands of quasars in the starry sky. These strange ones are incredible bright objects are called beacons of the Universe. They allow us to imagine the structure of the cosmos a little better and come closer to the moment from which it all began.
Although astrophysicists had been receiving indirect evidence for many years of the existence of supermassive invisible objects in the Universe, the term “black hole” did not exist until 1967. To avoid complex names, American physicist John Archibald Wheeler proposed calling such objects “black holes.” Why not? To some extent they are black, because we cannot see them. Besides, they attract everything, you can fall into them, just like into a real hole. Yes, and get out of such a place according to modern laws physics is simply impossible. However, Stephen Hawking claims that when traveling through a black hole, you can get to another Universe, another world, and this is hope.
Fear of Infinity
Due to the excessive mystery and romanticization of black holes, these objects have become a real horror story among people. The yellow press likes to speculate on the illiteracy of the population, publishing amazing stories about how a huge black hole is moving towards our Earth, which in a matter of hours will swallow solar system, or simply emits waves of toxic gas towards our planet.
The topic of destroying the planet with the help of the Large Hadron Collider, which was built in Europe in 2006 on the territory of the European Council for Nuclear Research (CERN), is especially popular. The wave of panic began as someone's stupid joke, but grew like a snowball. Someone started a rumor that a black hole could form in the particle accelerator of the collider, which would swallow our planet entirely. Of course, the indignant people began to demand a ban on experiments at the LHC, fearing this outcome of events. The European Court began to receive lawsuits demanding that the collider be closed and the scientists who created it punished to the fullest extent of the law.
In fact, physicists do not deny that when particles collide in the Large Hadron Collider, objects similar in properties to black holes can arise, but their size is at the level of the size of elementary particles, and such “holes” exist for such a short time that we can’t even record their occurrence.
One of the main experts who are trying to dispel the wave of ignorance in front of people is Stephen Hawking, a famous theoretical physicist who, moreover, is considered a real “guru” regarding black holes. Hawking proved that black holes do not always absorb the light that appears in the accretion disks, and some of it is scattered into space. This phenomenon was called Hawking radiation, or black hole evaporation. Hawking also established a relationship between the size of a black hole and the rate of its “evaporation” - the smaller it is, the less time it exists. This means that all opponents of the Large Hadron Collider should not worry: black holes in it will not be able to survive even a millionth of a second.
Theory not proven in practice
Unfortunately, human technology at this stage of development does not allow us to test most of the theories developed by astrophysicists and other scientists. On the one hand, the existence of black holes has been quite convincingly proven on paper and derived using formulas in which everything fits with each variable. On the other hand, in practice we have not yet been able to see a real black hole with our own eyes.
Despite all the disagreements, physicists suggest that in the center of each galaxy there is a supermassive black hole, which gathers stars into clusters with its gravity and forces them to travel around the Universe in a large and friendly company. In our Milky Way galaxy, according to various estimates, there are from 200 to 400 billion stars. All these stars are orbiting something that has enormous mass, something that we can't see with a telescope. WITH a large share It's probably a black hole. Should we be afraid of her? – No, at least not in the next few billion years, but we can make another interesting film about it.
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. Most clear example in the history of modern physics - a long-term lack of interest in black holes and extreme states 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 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 Church of England, was completely undeservedly lost among the stars English science XVIII 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 tiny particles. Michell suggested that light corpuscles, like ordinary matter, obey the laws of mechanics. The consequence of this hypothesis turned out to be quite nontrivial - celestial bodies can turn into light traps.
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 critical value 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, 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 at all in terms of 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 nuclear fuel sheds its shell and turns into a slowly cooling star. 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. Therefore, a natural question arose: is there upper limit masses for the 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 rough calculations by Oppenheimer and his graduate student George Volkow, it followed that the most massive supernova descendants do not become neutron stars, but pass into some other state. In 1939, Oppenheimer and Hartland Snyder used an idealized model to prove that a massive collapsing star is pulled toward 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 the right area, 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 electric 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 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 direct relation to fate material bodies, falling deep into 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 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 the same way as absolutely black body, heated to a temperature 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 length Planck-Wheeler, the hole loses stability and explodes, releasing the same energy as a 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 upper limit masses 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 constant h, speed of light C and 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 strict evidence The presence of at least one such object in space has not yet been found. However, it is very likely that in some dual systems The sources of X-ray radiation 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 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 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 additional dimensions, because they are looped on such a small scale that our instruments do not 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 dimensions it is 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, which will be easy 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 such holes will also be able to be detected by orbital detectors. cosmic rays new generation.
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 that we talked about are completely atypical. real world. Collapsed stars typically rotate and may also have an electrical charge.
Theorem about baldness
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 true, special case 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, however, 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, That centrifugal forces, on the contrary, contribute to their care in open 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 gas molecule, particle 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, inner zone The disk is held 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 there is. The degree of chaos is expressed quite concretely 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? Alas, 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. Entropy of the ordinary physical body more or less proportional to its volume, and the entropy of the 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. This 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 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 hard surface, but the hole does not have one. The fall of matter onto the surface of a neutron star entails thermonuclear explosions, which generate periodic X-ray flashes 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. This is what the professor of theoretical physics at the University of California told us. Institute of Technology Kip Thorne:
“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 recent years, considerable attention has been paid to models of black holes in multidimensional spaces, which naturally appear in string theory. But these studies no longer belong to classical studies, but to quantum holes, has not yet been discovered. The main result recent years- 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 earthly matter. Stephen Hawking recently sent out a preprint of a paper showing that the thermal radiation from a black hole is completely returned to outside 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 were confident 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.”
The hypothesis of the existence of black holes was first put forward by the English astronomer J. Michell in 1783 based on corpuscular theory light and Newton's theory of gravity. At that time, Huygens' wave theory and his famous wave principle were simply forgotten. Didn't help wave theory support of some venerable scientists, in particular famous St. Petersburg academicians M.V. Lomonosov and L. Euler. The logic of reasoning that led Michell to the concept of a black hole is very simple: if light consists of particles-corpuscles of the luminiferous ether, then these particles should experience, like other bodies, attraction from the gravitational field. Consequently, the more massive the star (or planet), the greater the attraction from its side the corpuscles should experience and the more difficult it is for light to leave the surface of such a body.
Further logic suggests that such massive stars, the attraction of which the corpuscles will no longer be able to overcome, and they will always appear black to an external observer, although they themselves can glow with a dazzling brilliance, like the Sun. Physically, this means that the second escape velocity on the surface of such a star should be no less than the speed of light. Michell's calculations show that light will never leave a star if its radius at average solar density is equal to 500 solar. This kind of star can already be called a black hole.
After 13 years, the French mathematician and astronomer P.S. Laplace, most likely, independently of Michell, expressed a similar hypothesis about the existence of such exotic objects. Using a cumbersome calculation method, Laplace found the radius of a ball for a given density, on the surface of which the parabolic speed is equal to the speed of light. According to Laplace, corpuscles of light, being gravitating particles, should be delayed by massive stars emitting light, which have a density equal to that of the Earth, and a radius 250 times greater than that of the Sun.
This theory of Laplace was included only in the first two lifetime editions of his famous book “Exposition of the World System,” published in 1796 and 1799. Yes, perhaps, the Austrian astronomer F. K. von Zach became interested in Laplace’s theory, publishing it in 1798 under the title “Proof of the theorem that the gravitational force of a heavy body can be so great that light cannot flow out of it.”
At this point, the history of black hole research paused for more than 100 years. It seems that Laplace himself quietly abandoned such an extravagant hypothesis, since he excluded it from all others lifetime publications his book, which was published in 1808, 1813 and 1824. Perhaps Laplace did not want to further replicate the almost fantastic hypothesis about colossal stars that do not release light. Perhaps he was stopped by new astronomical data on the invariability of the magnitude of light aberration in different stars, which contradicted some of the conclusions of his theory, on the basis of which he based his calculations. But most probable cause the fact that everyone has forgotten about the mysterious hypothetical objects of Michell-Laplace is the triumph of the wave theory of light, triumphal procession which began with the first years XIX V.
This triumph began with the Booker lecture of the English physicist T. Young “The Theory of Light and Color”, published in 1801, where Young boldly, contrary to Newton and other famous supporters of the corpuscular theory (including Laplace), outlined the essence of the wave theory of light, saying that the light emitted consists of the wave-like movements of the luminiferous ether. Laplace, inspired by the discovery of the polarization of light, began to “save” corpuscles by constructing a theory of double refraction of light in crystals based on the double action of crystal molecules on light corpuscles. But subsequent works of physicists O.Zh. Fresnel, F.D. Aragon, J. Fraunhofer and others left no stone unturned from the corpuscular theory, which was seriously remembered only a century later, after the discovery of quanta. All discussions about black holes within the framework of the wave theory of light looked ridiculous at that time.
They did not immediately remember about black holes even after the “rehabilitation” of the corpuscular theory of light, when they started talking about it in the new quality level thanks to the hypothesis of quanta (1900) and photons (1905). Black holes were rediscovered for the second time only after the creation of General Relativity in 1916, when the German theoretical physicist and astronomer K. Schwarzschild, a few months after the publication of Einstein’s equations, used them to study the structure of curved space-time in the vicinity of the Sun. He ended up rediscovering the phenomenon of black holes, but on a deeper level.
The final theoretical discovery of black holes came in 1939, when Oppenheimer and Snyder made the first explicit solution of Einstein's equations to describe the formation of a black hole from a collapsing cloud of dust. The term “black hole” itself was first introduced into science by the American physicist J. Wheeler in 1968, during the years of rapid revival of interest in general relativity, cosmology and astrophysics, caused by the achievements of extra-atmospheric (in particular, X-ray) astronomy, the discovery cosmic microwave background radiation, pulsars and quasars.
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 the history of modern physics is the 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 initial speed will exceed the value now called the second escape velocity and escape speed. 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 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 pulled toward 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 will never 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 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—the physical vacuum—is actually not empty at all. Due to quantum fluctuations of various fields in a vacuum, many virtual particles. 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 the 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 radiation 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 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 high energy so that their collision would create 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 superstring theory, which includes quantum theory gravity (though far from complete). According to this theory, space has not three dimensions, but at least nine. We do not notice additional dimensions because they are looped on such a small scale that our instruments do not 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. 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. More on this in the next issue.
