Of all the hypothetical objects in the universe predicted by scientific theories, black holes make the most eerie impression. And, although assumptions about their existence began to be expressed almost a century and a half before Einstein's publication of general relativity, convincing evidence of the reality of their existence was obtained quite recently.
Let's start by looking at how general relativity addresses the question of the nature of gravity. Newton's law of gravity states that a force of mutual attraction acts between any two massive bodies in the Universe. Because of this gravitational attraction, the Earth revolves around the Sun. General relativity forces us to look at the Sun-Earth system differently. According to this theory, in the presence of such a massive celestial body as the Sun, space-time seems to be perforated under its weight, and the uniformity of its tissue is disturbed. Imagine an elastic trampoline with a heavy ball (for example, from a bowling alley) resting on it. The stretched fabric bends under its weight, creating a vacuum around it. In the same way, the Sun pushes space-time around itself.
According to this picture, the Earth simply rolls around the formed funnel (except that a small ball rolling around a heavy one on a trampoline will inevitably lose speed and spiral closer to a large one). And what we habitually perceive as the force of gravity in our everyday life is also nothing more than a change in the geometry of space-time, and not a force in Newtonian understanding. To date, no more successful explanation of the nature of gravity than the general theory of relativity gives us has not been invented.
Now imagine what will happen if we - within the framework of the proposed picture - increase and increase the mass of a heavy ball without increasing its physical size? Being absolutely elastic, the funnel will deepen until its upper edges converge somewhere high above the completely heavy ball, and then it simply ceases to exist when viewed from the surface. In the real Universe, having accumulated a sufficient mass and density of matter, the object slams a space-time trap around itself, the fabric of space-time closes, and it loses its connection with the rest of the Universe, becoming invisible to it. This is how a black hole appears.
Schwarzschild and his contemporaries believed that such strange space objects did not exist in nature. Einstein himself not only held 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 spent nuclear fuel sheds its shell and turns into a slowly cooling white dwarf only if its mass is less than 1.4 times the mass of the Sun. 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 the work of Chandrasekhar, it was obvious that only stars with a mass of more than 1.4 solar masses can undergo such an evolution. Therefore, a natural question arose - is there an upper mass limit for supernovae that leave behind neutron stars?
In the late 1930s, the future father of the American atomic bomb, Robert Oppenheimer, established that such a limit does exist and does not exceed a few 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 Ms. But even from the approximate calculations of Oppenheimer and his graduate student George Volkov, it followed that the most massive descendants of supernovae do not become neutron stars, but go into some other state. In 1939, Oppenheimer and Hartland Snyder, using an idealized model, proved that a massive collapsing star is contracting 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.
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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 substance. As a result, a singularity arises, a "superconcentrate" of the gravitational field, closed in an infinitely small volume. For a stationary hole, this is a point, for a rotating one, a ring. The curvature of space-time and, consequently, the gravitational force near the singularity tend to infinity. At the end of 1967, the American physicist John Archibald Wheeler was the first to call such a final stellar collapse a black hole. The new term fell in love with 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).
The most important property of a black hole is that whatever gets into it, it won't come back. This even applies to light, which is why black holes got their name: a body that absorbs all the light falling on it and does not emit its own seems to be absolutely black. According to general relativity, if an object approaches the center of a black hole at a critical distance - this distance is called the Schwarzschild radius - it can never go back. (The German astronomer Karl Schwarzschild (1873-1916) in the last years of his life, using the equations of Einstein's general theory of relativity, calculated the gravitational field around a mass of zero volume.) For the mass of the Sun, the Schwarzschild radius is 3 km, that is, to turn our The sun is in a black hole, you need to compact its entire mass to the size of a small town!
Inside the Schwarzschild radius, the theory predicts even stranger phenomena: all the matter of a black hole collects into an infinitely small point of infinite density at its very center - mathematicians call such an object a singular perturbation. With an infinite density, any finite mass of matter, mathematically speaking, occupies zero spatial volume. Whether this phenomenon actually occurs inside a black hole, we, naturally, cannot experimentally check, since everything that got inside the Schwarzschild radius does not come back.
Thus, not having the opportunity to “examine” a black hole in the traditional sense of the word “look”, we, nevertheless, can detect its presence by indirect signs of the influence of its super-powerful and completely unusual gravitational field on the matter around it.
Supermassive black holes
At the center of our Milky Way and other galaxies is an incredibly massive black hole millions of times heavier than the Sun. These supermassive black holes (as they got this name) were discovered by observing the nature of the movement of interstellar gas near the centers of galaxies. Gases, judging by observations, rotate at a close distance from a supermassive object, and simple calculations using the laws of Newtonian mechanics show that the object that attracts them, with a meager diameter, has a monstrous mass. Only a black hole can spin the interstellar gas in the center of the galaxy this way. In fact, astrophysicists have already found dozens of such massive black holes in the centers of neighboring galaxies, and strongly suspect that the center of any galaxy is a black hole.
Stellar mass black holes
According to our current ideas about the evolution of stars, when a star with a mass exceeding about 30 times the mass of the Sun dies in a supernova explosion, its outer shell scatters, and its inner layers rapidly collapse towards the center and form a black hole in place of the star that has used up its fuel reserves. It is practically impossible to detect a black hole of this origin isolated in interstellar space, since it is in a rarefied vacuum and does not manifest itself in any way in terms of gravitational interactions. However, if such a hole was part of a binary star system (two hot stars orbiting around their center of mass), the black hole will still exert a gravitational effect on its twin star. Astronomers today have more than a dozen candidates for the role of star systems of this kind,although strong evidence has not been obtained for any of them.
In a binary system with a black hole in its composition, the substance of the "living" star will inevitably "flow" in the direction of the black hole. And the substance sucked out by the black hole will swirl when falling into the black hole in a spiral, disappearing when crossing the Schwarzschild radius. When approaching the fatal boundary, however, the substance sucked into the black hole's funnel will inevitably thicken and heat up due to the increased frequency of collisions between the particles absorbed by the hole, until it warms up to the energies of wave radiation in the X-ray range of the electromagnetic spectrum. Astronomers can measure the periodicity of changes in the intensity of X-rays of this kind and calculate, comparing it with other available data, the approximate mass of an object "pulling" matter onto itself. If the mass of the object exceeds the Chandrasekhar limit (1.4 solar masses),this object cannot be a white dwarf, in which our star is destined to degenerate. In most of the identified cases of observation of such binary X-ray stars, a neutron star is a massive object. However, more than a dozen cases have already been counted when the only reasonable explanation is the presence of a black hole in a binary star system.
All other types of black holes are much more speculative and based solely on theoretical research - there is no experimental evidence of their existence at all. First, these are black mini-holes with a mass comparable to the mass of a mountain and compressed to the radius of a proton. The idea of their origin at the initial stage of the formation of the Universe immediately after the Big Bang was expressed by the English cosmologist Stephen Hawking (see The Hidden Principle of the Irreversibility of Time). Hawking suggested that mini-hole explosions could explain the truly mysterious phenomenon of chiseled gamma-ray bursts in the Universe. Secondly, some theories of elementary particles predict the existence in the Universe - at the micro-level - of a real sieve of black holes, which are a kind of foam from the waste of the universe. The diameter of such micro-holes is supposedly about 10–33 cm - they are billions of times smaller than a proton. At the moment, we do not have any hopes for experimental verification of even the very fact of the existence of such black hole particles, let alone somehow investigating their properties.
And what happens to the observer if he suddenly finds himself on the other side of the gravitational radius, otherwise called the event horizon. This is where the most amazing property of black holes begins. It is not for nothing that we have always mentioned time, or rather space-time, when speaking of black holes. According to Einstein's theory of relativity, the faster a body moves, the more its mass becomes, but the slower time begins to pass! At low speeds, under normal conditions, this effect is invisible, but if the body (spacecraft) moves at a speed close to the speed of light, then its mass increases, and time slows down! When the speed of the body is equal to the speed of light, the mass goes to infinity, and time stops! This is evidenced by rigorous mathematical formulas. Let's go back to the black hole. Let's imagine a fantastic situationwhen a spaceship with astronauts on board approaches its gravitational radius or event horizon. It is clear that the event horizon is so named because we can observe any events (generally observe something) only up to this border. That we are not in a position to observe this border. Nevertheless, being inside the spacecraft approaching the black hole, the astronauts will feel the same as before, because on their watch the time will run "normally". The spacecraft will calmly cross the event horizon and move on. But since its speed will be close to the speed of light, the spaceship will reach the center of the black hole, literally, in a moment.that we can observe any events (generally observe something) only up to this border. That we are not in a position to observe this border. Nevertheless, being inside the spacecraft approaching the black hole, the astronauts will feel the same as before, because on their watch the time will run "normally". The spacecraft will calmly cross the event horizon and move on. But since its speed will be close to the speed of light, the spaceship will reach the center of the black hole, literally, in a moment.that we can observe any events (generally observe something) only up to this border. That we are not in a position to observe this border. Nevertheless, being inside the spacecraft approaching the black hole, the astronauts will feel the same as before, because on their watch the time will run "normally". The spacecraft will calmly cross the event horizon and move on. But since its speed will be close to the speed of light, the spaceship will reach the center of the black hole, literally, in a moment. But since its speed will be close to the speed of light, the spaceship will reach the center of the black hole, literally, in a moment. But since its speed will be close to the speed of light, the spaceship will reach the center of the black hole, literally, in a moment.
And for an outside observer, the spacecraft will simply stop on the event horizon, and will stay there almost forever! This is the paradox of the colossal gravitation of black holes. The question is natural, will the astronauts survive, going to infinity according to the clock of an external observer. Not. And the point is not at all the enormous gravitation, but the tidal forces, which in such a small and massive body vary greatly at small distances. When an astronaut is 1 m 70 cm tall, the tidal forces at his head will be much less than at his feet and he will simply be torn apart on the event horizon. So, in general terms, we figured out what black holes are, but so far we were talking about black holes of stellar mass. Currently, astronomers have managed to find supermassive black holes, the mass of which can be a billion suns!Supermassive black holes do not differ in properties from their smaller counterparts. They are only much more massive and, as a rule, are located in the centers of galaxies - the stellar islands of the Universe. In the center of Our Galaxy (Milky Way) there is also a supermassive black hole. The colossal mass of such black holes will make it possible to search for them not only in Our Galaxy, but also in the centers of distant galaxies located at a distance of millions and billions of light years from the Earth and the Sun. European and American scientists have conducted a global search for supermassive black holes, which, according to modern theoretical calculations, should be located in the center of every galaxy. The colossal mass of such black holes will make it possible to search for them not only in Our Galaxy, but also in the centers of distant galaxies located at a distance of millions and billions of light years from the Earth and the Sun. European and American scientists have conducted a global search for supermassive black holes, which, according to modern theoretical calculations, should be located in the center of every galaxy. The colossal mass of such black holes will make it possible to search for them not only in Our Galaxy, but also in the centers of distant galaxies located at a distance of millions and billions of light years from the Earth and the Sun. European and American scientists have conducted a global search for supermassive black holes, which, according to modern theoretical calculations, should be located in the center of every galaxy.
Modern technology makes it possible to detect the presence of these collapsars in neighboring galaxies, but very few of them have been detected. This means that either black holes are simply hiding in dense gas and dust clouds in the central part of galaxies, or they are located in more distant corners of the Universe. So, black holes can be detected by the X-ray radiation emitted during the accretion of matter on them, and in order to census such sources, satellites with X-ray telescopes on board were launched into near-Earth comic space. While searching for X-ray sources, the space observatories Chandra and Rossi found that the sky was filled with background X-rays and was millions of times brighter than visible light. Much of this background X-ray radiation from the sky must come from black holes. Usually in astronomy they talk about three types of black holes. The first is black holes of stellar masses (about 10 solar masses). They are formed from massive stars when they run out of thermonuclear fuel. The second is supermassive black holes at the centers of galaxies (masses from a million to billions of the sun). And finally, there are primordial black holes formed at the beginning of the life of the Universe, the masses of which are small (of the order of the mass of a large asteroid). Thus, a large range of possible black hole masses remains unfilled. But where are these holes? By filling the space with X-rays, they nevertheless do not want to show their true "face". But in order to build a clear theory of the relationship between background X-ray radiation and black holes, you need to know their number. At the moment, space telescopes have managed to detect only a small number of supermassive black holes, the existence of which can be considered proven. Indirect signs allow us to bring the number of observed black holes responsible for background radiation to 15%. One has to assume that the rest of the supermassive black holes are simply hiding behind a thick layer of dust clouds that only transmit high-energy X-rays or are too far to be detected by modern observing means.that the rest of the supermassive black holes are simply hiding behind a thick layer of dusty clouds that only allow high-energy X-rays to pass through or are too far away to be detected by modern observing devices.that the rest of the supermassive black holes are simply hiding behind a thick layer of dusty clouds that only allow high-energy X-rays to pass through, or are too far away to be detected by modern observing devices.
Supermassive black hole (neighborhood) at the center of galaxy M87 (X-ray image). An ejection (jet) from the event horizon is visible. Image from the site www.college.ru/astronomy
Finding hidden black holes is one of the main challenges of modern X-ray astronomy. The latest breakthroughs in this area, associated with research with the Chandra and Rossi telescopes, however, cover only the low-energy range of X-rays - approximately 2000–20,000 electron-volts (for comparison, the energy of optical radiation is about 2 electron-volts). volt). Essential amendments to these studies can be made by the European space telescope "Integral", which is able to penetrate into the still insufficiently studied region of X-rays with energies of 20,000-300,000 electron-volts. The importance of studying this type of X-rays is that, although the X-ray background of the sky is of low energy, multiple peaks (points) of radiation with an energy of about 30,000 electron-volts appear against this background. Scientists are still just opening the veil of the mystery of what gives rise to these peaks, and Integral is the first sufficiently sensitive telescope capable of finding such sources of X-rays. According to astronomers, high-energy rays give rise to the so-called Compton-thick objects, that is, supermassive black holes enveloped in a dusty shell. It is the Compton objects that are responsible for the 30,000 electron-volt X-ray peaks in the background radiation field. It is the Compton objects that are responsible for the 30,000 electron-volt X-ray peaks in the background radiation field. It is the Compton objects that are responsible for the 30,000 electron-volt X-ray peaks in the background radiation field.
But, continuing research, scientists came to the conclusion that Compton objects make up only 10% of the number of black holes that should create high-energy peaks. This is a serious obstacle to the further development of the theory. So the missing X-rays are not coming from Compton-thick, but from ordinary supermassive black holes? Then what about the dust curtains for low energy X-rays? The answer seems to lie in the fact that many black holes (Compton objects) have had enough time to absorb all the gas and dust that enveloped them, but before that they had the opportunity to declare themselves with high-energy X-rays. After absorbing all the matter, such black holes were already unable to generate X-rays on the event horizon. It becomes clear why these black holes cannot be detected,and it becomes possible to attribute the missing sources of background radiation to their account, since although the black hole no longer emits, the radiation previously created by it continues its journey through the Universe. However, it is entirely possible that the missing black holes are more hidden than astronomers assume, that is, the fact that we do not see them does not mean that they are not. We just don't have enough observing power to see them. Meanwhile, NASA scientists plan to expand the search for hidden black holes even further into the universe. It is there that the underwater part of the iceberg is located, they say. For several months, research will be carried out as part of the Swift mission. Penetration into the deep universe will reveal hiding black holes,find the missing link for background radiation and shed light on their activity in the early Universe.
Some black holes are considered more active than their quiet neighbors. Active black holes absorb the surrounding matter, and if a "gape" star flying past gets into the flight of gravity, it will certainly be "eaten" in the most barbaric way (torn to shreds). The absorbed substance, falling onto the black hole, heats up to enormous temperatures, and experiences a flash in the gamma, X-ray and ultraviolet ranges. There is also a supermassive black hole in the center of the Milky Way, but it is more difficult to study than holes in nearby or even distant galaxies. This is due to a dense wall of gas and dust that stands in the way of the center of our Galaxy, because the solar system is located almost at the edge of the galactic disk. Therefore, observations of the activity of black holes are much more effective in those galaxies whose core is clearly visible. When observing one of the distant galaxies located in the constellation Bootes at a distance of 4 billion light years, astronomers for the first time managed to trace from the beginning and almost to the end the process of absorption of a star by a supermassive black hole. For thousands of years, this giant collapsar rested quietly in the center of an unnamed elliptical galaxy, until one of the stars dared to get close enough to it.
The black hole's powerful gravity tore the star apart. Clumps of matter began to fall on the black hole and, upon reaching the event horizon, flare up brightly in the ultraviolet range. These flares were recorded by NASA's new space telescope Galaxy Evolution Explorer, which studies the sky in ultraviolet light. The telescope continues to observe the behavior of the distinguished object even today. the black hole's meal is not over yet, and the remains of the star continue to fall into the abyss of time and space. Observations of such processes will ultimately help to better understand how black holes evolve with their parent galaxies (or, conversely, galaxies evolve with their parent black hole). Earlier observations show that such excesses are not uncommon in the universe. Scientists have calculatedthat, on average, a star is absorbed by a supermassive black hole of a typical galaxy once every 10,000 years, but since there are a large number of galaxies, star absorption can be observed much more often.