Black hole astronomy. Black hole in space
BLACK HOLE
a region in space resulting from the complete gravitational collapse of matter, in which the gravitational attraction is so strong that neither matter, nor light, nor other information carriers can leave it. Therefore, the interior of a black hole is not causally connected to the rest of the Universe; Physical processes occurring inside a black hole cannot influence processes outside it. A black hole is surrounded by a surface with the property of a unidirectional membrane: matter and radiation freely fall through it into the black hole, but nothing can escape from there. This surface is called the "event horizon". Since there are still only indirect indications of the existence of black holes at distances of thousands of light years from the Earth, our further presentation is based mainly on theoretical results. Black holes, predicted by the general theory of relativity (the theory of gravity proposed by Einstein in 1915) and other, more modern theories of gravity, were mathematically substantiated by R. Oppenheimer and H. Snyder in 1939. But the properties of space and time in the vicinity of these objects turned out to be so unusual, that astronomers and physicists did not take them seriously for 25 years. However, astronomical discoveries in the mid-1960s brought black holes to the surface as a possible physical reality. Their discovery and study can fundamentally change our ideas about space and time.
Formation of black holes. While thermonuclear reactions occur in the bowels of the star, they maintain high temperature and pressure, preventing the star from collapsing under the influence of its own gravity. However, over time, the nuclear fuel is depleted, and the star begins to shrink. Calculations show that if the mass of a star does not exceed three solar masses, then it will win the “battle with gravity”: its gravitational collapse will be stopped by the pressure of “degenerate” matter, and the star will forever turn into a white dwarf or neutron star. But if the mass of the star is more than three solar, then nothing can stop its catastrophic collapse and it will quickly go under the event horizon, becoming a black hole. For a spherical black hole of mass M, the event horizon forms a sphere with a circle at the equator 2p times larger than the “gravitational radius” of the black hole RG = 2GM/c2, where c is the speed of light and G is the gravitational constant. A black hole with a mass of 3 solar masses has a gravitational radius of 8.8 km.
If an astronomer observes a star at the moment of its transformation into a black hole, then at first he will see how the star is compressing faster and faster, but as its surface approaches the gravitational radius, the compression will begin to slow down until it stops completely. At the same time, the light coming from the star will weaken and redden until it goes out completely. This happens because, in the fight against the gigantic force of gravity, the light loses energy and it takes more and more time for it to reach the observer. When the star's surface reaches the gravitational radius, the light that leaves it will take an infinite amount of time to reach the observer (and the photons will lose all their energy). Consequently, the astronomer will never wait for this moment, much less see what is happening to the star below the event horizon. But theoretically this process can be studied. Calculation of idealized spherical collapse shows that a short time the star contracts to a point where it reaches infinitely large values density and gravity. Such a point is called "singularity". Moreover, general mathematical analysis shows that if an event horizon has arisen, then even a non-spherical collapse leads to a singularity. However, all this is true only if general relativity applies down to very small spatial scales, which we are not yet sure of. Quantum laws operate in the microworld, but the quantum theory of gravity has not yet been created. It is clear that quantum effects cannot stop the collapse of a star into a black hole, but they could prevent the appearance of a singularity. The modern theory of stellar evolution and our knowledge of the stellar population of the Galaxy indicate that among its 100 billion stars there should be about 100 million black holes formed during the collapse of the most massive stars. In addition, black holes of very large masses can be located in the cores of large galaxies, including ours. As already noted, in our era, only a mass more than three times the solar mass can become a black hole. However, immediately after the Big Bang, from which approx. 15 billion years ago, the expansion of the Universe began, black holes of any mass could be born. The smallest of them, due to quantum effects, should have evaporated, losing their mass in the form of radiation and particle flows. But “primary black holes” with a mass of more than 1015 g could survive to this day. All calculations of stellar collapse are made under the assumption of a slight deviation from spherical symmetry and show that an event horizon is always formed. However, with a strong deviation from spherical symmetry, the collapse of a star can lead to the formation of a region with infinitely strong gravity, but not surrounded by an event horizon; it is called the “naked singularity.” This is no longer a black hole in the sense we discussed above. Physical laws near a naked singularity can take a very unexpected form. Currently, a naked singularity is considered an unlikely object, while most astrophysicists believe in the existence of black holes.
Properties of black holes. To an outside observer, the structure of a black hole looks extremely simple. During the collapse of a star into a black hole in a small fraction of a second (according to a remote observer's clock), all its external features associated with the inhomogeneity of the original star are emitted in the form of gravitational and electromagnetic waves. The resulting stationary black hole “forgets” all information about the original star, except for three quantities: total mass, angular momentum (associated with rotation), and electric charge. By studying a black hole, it is no longer possible to know whether the original star consisted of matter or antimatter, whether it had the shape of a cigar or a pancake, etc. Under real astrophysical conditions, a charged black hole will attract particles of the opposite sign from the interstellar medium, and its charge will quickly become zero. The remaining stationary object will either be a non-rotating "Schwarzschild black hole", which is characterized only by mass, or a rotating "Kerr black hole", which is characterized by mass and angular momentum. The uniqueness of the above types of stationary black holes was proven within the framework of the general theory of relativity by W. Israel, B. Carter, S. Hawking and D. Robinson. According to the general theory of relativity, space and time are curved by the gravitational field of massive bodies, with the greatest curvature occurring near black holes. When physicists talk about intervals of time and space, they mean numbers read from some physical clock or ruler. For example, the role of a clock can be played by a molecule with a certain vibration frequency, the number of which between two events can be called a “time interval”. It is remarkable that gravity affects all physical systems in the same way: all clocks show that time is slowing down, and all rulers show that space is stretching near a black hole. This means that the black hole bends the geometry of space and time around itself. Far from the black hole, this curvature is small, but close to it it is so large that light rays can move around it in a circle. Far from a black hole, its gravitational field is exactly described by Newton's theory for a body of the same mass, but close to it, gravity becomes much stronger than Newton's theory predicts. Any body falling into a black hole will be torn apart long before crossing the event horizon by powerful tidal gravitational forces arising from differences in gravity at different distances from the center. A black hole is always ready to absorb matter or radiation, thereby increasing its mass. Its interaction with the outside world is determined simple principle Hawking: The area of the event horizon of a black hole never decreases, unless one takes into account the quantum production of particles. J. Bekenstein in 1973 suggested that black holes obey the same physical laws as physical bodies, emitting and absorbing radiation (the “absolutely black body” model). Influenced by this idea, Hawking showed in 1974 that black holes can emit matter and radiation, but this will only be noticeable if the mass of the black hole itself is relatively small. Such black holes could be born immediately after the Big Bang, which began the expansion of the Universe. The masses of these primary black holes should be no more than 1015 g (like a small asteroid), and their size should be 10-15 m (like a proton or neutron). The powerful gravitational field near a black hole produces particle-antiparticle pairs; one of the particles of each pair is absorbed by the hole, and the second is emitted outward. A black hole with a mass of 1015 g should behave like a body with a temperature of 1011 K. The idea of \u200b\u200b“evaporation” of black holes completely contradicts the classical concept of them as bodies that are not capable of radiating.
Search for black holes. Calculations within the framework of Einstein's general theory of relativity only indicate the possibility of the existence of black holes, but do not at all prove their presence in the real world; the discovery of a real black hole would be an important step in the development of physics. Finding isolated black holes in space is hopelessly difficult: we will not be able to notice a small dark object against the background of cosmic blackness. But there is hope to detect a black hole by its interaction with surrounding astronomical bodies, by its characteristic influence on them. Supermassive black holes can reside in the centers of galaxies, continuously devouring stars there. Concentrated around the black hole, the stars should form central brightness peaks in the galactic nuclei; Their search is now actively underway. Another search method is to measure the speed of stars and gas around a central object in the galaxy. If their distance from the central object is known, then its mass and average density can be calculated. If it significantly exceeds the density possible for star clusters, then it is believed that it is a black hole. Using this method, in 1996 J. Moran and his colleagues determined that in the center of the galaxy NGC 4258 there is probably a black hole with a mass of 40 million solar. The most promising is to search for a black hole in binary systems, where it, paired with a normal star, can orbit around a common center of mass. By the periodic Doppler shift of lines in the spectrum of a star, one can understand that it is orbiting in tandem with a certain body and even estimate the mass of the latter. If this mass exceeds 3 solar masses, and the radiation of the body itself cannot be detected, then it is very possible that it is a black hole. In a compact binary system, the black hole can capture gas from the surface of a normal star. Moving in orbit around the black hole, this gas forms a disk and, as it spirals toward the black hole, it becomes very hot and becomes a source of powerful X-ray radiation. Rapid fluctuations in this radiation should indicate that the gas is rapidly moving in a small radius orbit around a tiny, massive object. Since the 1970s, several X-ray sources have been discovered in binary systems with clear signs the presence of black holes. The most promising is the X-ray binary V 404 Cygni, the mass of the invisible component of which is estimated to be no less than 6 solar masses. Other remarkable black hole candidates are in the X-ray binary systems Cygnus X-1, LMCX-3, V 616 Monoceros, QZ Chanterelles, and the X-ray novae Ophiuchus 1977, Mucha 1981, and Scorpio 1994. The exception is LMCX-3, located in the Bolshoi Magellanic Cloud, all of them are located in our Galaxy at distances of about 8000 light years. years from Earth.
see also
COSMOLOGY;
GRAVITY;
GRAVITATIONAL COLLAPSE;
RELATIVITY;
EXTRA-ATMOSPHERE ASTRONOMY.
LITERATURE
Cherepashchuk A.M. Masses of black holes in binary systems. Advances in Physical Sciences, vol. 166, p. 809, 1996
Collier's Encyclopedia. - Open Society. 2000 .
Synonyms:See what a “BLACK HOLE” is in other dictionaries:
BLACK HOLE, a localized area of outer space from which neither matter nor radiation can escape, in other words, the first cosmic speed exceeds the speed of light. The boundary of this area is called the event horizon.... ... Scientific and technical encyclopedic dictionary
Cosmic an object that arises as a result of the compression of a body by gravity. forces to sizes smaller than its gravitational radius rg=2g/c2 (where M is the mass of the body, G is the gravitational constant, c is the numerical value of the speed of light). Prediction about the existence of... ... Physical encyclopedia
Noun, number of synonyms: 2 star (503) unknown (11) ASIS Dictionary of Synonyms. V.N. Trishin. 2013… Synonym dictionary
A black hole is a special region in space. This is a certain accumulation of black matter, capable of drawing into itself and absorbing other objects in space. The phenomenon of black holes is still not. All available data are just theories and assumptions of scientists astronomers.
The name "black hole" was coined by the scientist J.A. Wheeler in 1968 at Princeton University.
There is a theory that black holes are stars, but unusual ones, like neutron ones. A black hole - - because it has a very high luminescence density and sends out absolutely no radiation. Therefore, it is invisible neither in infrared, nor in x-rays, nor in radio rays.
The French astronomer P. Laplace discovered this situation 150 years before black holes. According to his arguments, if it has a density equal to the density of the Earth and a diameter 250 times greater than the diameter of the Sun, then it does not allow light rays to spread throughout the Universe due to its gravity, and therefore remains invisible. Thus, it is assumed that black holes are the most powerful emitting objects in the Universe, but they do not have a solid surface.
Properties of black holes
All supposed properties of black holes are based on the theory of relativity, derived in the 20th century by A. Einstein. Any traditional approach to studying this phenomenon does not provide any convincing explanation for the phenomenon of black holes.
The main property of a black hole is the ability to bend time and space. Any moving object caught in its gravitational field will inevitably be pulled in, because... in this case, a dense gravitational vortex, a kind of funnel, appears around the object. At the same time, the concept of time is transformed. Scientists, by calculation, are still inclined to conclude that black holes are not celestial bodies in the generally accepted sense. These are really some kind of holes, wormholes in time and space, capable of changing and compacting it.
A black hole is a closed region of space into which matter is compressed and from which nothing can escape, not even light.
According to astronomers' calculations, with the powerful gravitational field that exists inside black holes, not a single object can remain unharmed. It will instantly be torn into billions of pieces before it even gets inside. However, this does not exclude the possibility of exchanging particles and information with their help. And if a black hole has a mass at least a billion times greater than the mass of the Sun (supermassive), then it is theoretically possible for objects to move through it without being torn apart by gravity.
Of course, these are only theories, because scientists’ research is still too far from understanding what processes and capabilities black holes hide. It is quite possible that something similar could happen in the future.
Astronomers have discovered the most massive this moment object in the entire Universe. It turned out to be a superheavy black hole in the center of the galaxy NGC 1277 in the constellation Perseus, 228 million light years away from Earth.
The discovery was made by a group of German scientists from the Institute of Astronomy in Heidelberg during analyzes of images of the galaxy obtained using the infrared spectrometer of the Hobby-Eberly telescope. The black hole in the constellation Perseus contains a huge amount of matter - from 14 to 20 billion masses of our Sun, writes Rossiyskaya Gazeta.
It turned out that this mass is more than 14 percent of the mass of the entire galaxy, while supermassive black holes usually include about 0.1 percent. Previously, the heaviest object was considered to be a black hole in the galaxy NGC 4889, whose mass is 9.8 billion solar masses.
“This is a very strange galaxy indeed. It consists almost entirely of a black hole. “We may have discovered the first object from the class of black hole galaxies,” said astronomer Karl Gebhardt, one of the authors of the study. According to scientists, the results of the study can change the theory of the formation and growth of black holes.
According to scientists, the results of the study can change the theory of the formation and growth of black holes, notes the BBC.
Astrophysicists believe that there is always at least one black hole at the center of most massive galaxies. The nature of the formation of these objects is not yet completely clear. Black holes are thought to form through unlimited gravitational compression, often after the death of large stars. They create such a strong gravitational attraction that no substance, not even light, can leave them, the Saboteur clarifies.
Another discovery was made by astronomers at the European Southern Observatory, writes ukrinform.ua. They discovered an object also associated with a black hole - a quasar. With its gravity, the black hole destroys passing stars. The resulting stellar gas is gradually pulled into the hole, while simultaneously rotating. Compression and rapid rotation of the central part of the disk leads to its heating and powerful radiation. The black hole does not have time to absorb part of the matter, and it partially leaves it in the form of narrowly directed flows of gas and cosmic rays - this is called a quasar.
The found quasar is 5 times more powerful than those previously observed by scientists. The rate of ejection of matter from this quasar is two trillion times higher than the radiation of the Sun, and 100 times that of our entire galaxy. “I have been looking for such a monster for 10 years,” said one of the researchers, Professor Nahum Arav.
It is noted that the quasar is located 1000 light years from the supermassive black hole, and moves at a speed of 8 thousand kilometers per second.
Black holes in the Universe
In popular science literature and articles about the Universe you can often find the term “black hole”. The reader who reads this phrase for the first time immediately has an image of, say, a hole in the wall separating a dark room, otherwise, an ordinary hole. The mention of holes in the Universe is also initially associated with a certain hole in the heavens. The last judgment is partly true, but the physical essence of a black hole is much more complex than it might seem at first glance. So what is a black hole? IN modern science A black hole is usually called a region of space-time in which the gravitational field (gravity) is so strong that not a single object (even radiation) can escape from it. The name “black hole” was coined in 1968 by American physicist John A. Wheeler in his article about these amazing celestial objects. The new term immediately became popular, replacing the previously used names “collapsar” and “frozen star.” So, these celestial objects are simply something like a star (black balls?), but with a very strong gravitational field? But this will be too simple (and not entirely correct) description of perhaps the most mysterious objects in the Universe. To better understand what it is, let's go back briefly to the time of the great physicist Isaac Newton, who discovered the law of universal gravitation. The legend of the apple falling on Newton's head may be controversial, but be that as it may, genius guess scientist allowed us to deduce the law of universal force, to the action of which absolutely everything is subject! The gravitational field acts not only on volumetric bodies that are attracted to each other, but on microparticles and even light. This is very important point, most fundamentally related to the study of the properties of black holes. The first to admit the existence of invisible stars was the 18th-19th century scientist Pierre Simon Laplace (1749 - 1827), famous for creating the theory of the formation of planets in the solar system from rarefied matter (clouds). Laplace first wrote about invisible stars in 1795. Guided by the law of universal gravitation, he came to the conclusion that a star with a density equal to that of the Earth and a diameter 250 times greater than the diameter of the Sun does not allow a single light ray to reach us due to its gravity; Therefore, it is possible that the brightest celestial bodies in the Universe are invisible for this reason.
Look also at images of black holes (period - February 2004*February 2005) from the server of our colleagues Universe Today
Nowadays, any schoolchild who knows the basics of physics can prove this. Indeed, the larger the cosmic body, the greater the speed you need to gain in order to leave it forever. This speed is called the second cosmic speed, and for the Earth it is equal to 11 km/sec. But the greater the mass and the smaller the radius of the celestial body, the greater the second cosmic velocity, because With increasing mass, gravity increases, and with increasing distance from the center it weakens. On the Sun, the 2nd escape velocity is 620 km/sec, but on its surface. If we imagine that the Sun was compressed to a radius of 10 kilometers, while leaving the mass the same, then the 2nd cosmic speed will increase to half the speed of light or 150 thousand kilometers per second! This means that if the radius of the Sun is reduced even further (leaving the mass unchanged), then a moment will come when the second cosmic speed reaches light speed or 300,000 km/sec! Laplace, of course, did not take into account the compression of celestial bodies, which plays the most important role important role in the formation of black holes, but he made it possible to understand the main thing: a celestial body on the surface of which the second cosmic velocity exceeds the speed of light becomes invisible to an external observer! Otherwise, light tries to escape into space, but gravity does not allow it to do this, and from the outside we can only see black spot in space, to put it simply, a kind of hole! Similar conclusions were made by Laplace's contemporary, the English geologist J. Michell, in 1783, but his works are less known.
So, we are convinced that there can be invisible celestial bodies that actually exist, but cannot be observed from Earth due to the lack of radiation from them. All this seemed convincing before scientific world At the beginning of the 20th century, I did not become acquainted with the theory of another great physicist - Albert Einstein. But the persuasiveness of Laplace and Mitchell was still shaky for the simple reason that in their times they did not yet know that speeds higher than the speed of light simply do not exist in nature. The general theory of relativity has made it possible to take a big step towards defining a black hole in its modern understanding. To understand the essence of the difference between gravity according to Newton and gravity according to Einstein, let us return to the experiment with the compression of the Sun. Newton's law states that when we compress a body by half, gravity quadruples, but Einstein was able to brilliantly prove that gravity will increase faster, and the further we compress a body, the faster gravity will increase. If we follow Newtonian gravity, then gravity will become infinitely large if the radius becomes equal to 0. Einstein found that gravity becomes infinite at the so-called gravitational radius of the celestial body. The sphere is described by such a radius, also called the Schwarzschild sphere. Otherwise, the body will not shrink into a point, it will have certain dimensions, but gravity tends to infinity. The gravitational radius directly depends on the mass of the celestial body. For example, the gravitational radius of the Earth is 10 mm (currently 6400 km), and for the Sun it is 3000 m (700,000 km). So, the theory states that any celestial body (star, planet) that has contracted to a gravitational radius ceases to be a source of radiation, because light or any other radiation cannot leave given body due to the fact that the 2nd cosmic velocity from the gravitational radius and less will be higher than the speed of light. One question remains: what and how can compress a star to its gravitational radius. Answer: the star itself! While the star “lives,” thermonuclear reactions occur inside it, creating radiation fluxes to the surface of the gas ball. But the substance (hydrogen) for reactions is limited, and runs out over a period of several tens of millions to billions of years.
After the hydrogen fuel is consumed, the internal pressure created earlier by the reactions will disappear, and the star will begin to shrink under the influence of its own gravity, much like we squeeze a large piece of cotton wool with our hands. Some stars are contracting very quickly—catastrophically. A so-called gravitational collapse occurs. Having resolved the question of the compression of stars, we come to the most important thing - the question of the existence of black holes. We found out that theoretically such objects can exist, but how to find them practically? After all, according to the famous philosopher Confucius, you have to look for a black cat in a dark room, and it is unknown whether it is there at all. The search for mysterious objects began with X-ray radiation sources, i.e. those that emit the well-known X-ray rays, widely used in medicine to photograph bones and internal organs person. X-ray sources have a remarkable property: they emit only when the surrounding gas is heated to overheating. high temperatures. But to heat a gas to such a temperature, the gravitational field must be very strong. Such fields are possessed by collapsed stars (white dwarfs, neutron stars and... black holes!). But if white dwarfs can be observed directly, how can we detect a black hole? Astronomers have solved this problem too. It turns out that if a collapsed star has a mass twice that of the Sun, then it is the most likely candidate for a black hole. It is easiest to measure the mass of a celestial body if it exists in tandem with another, in other words, in a binary system by its orbital motion. The search for such binary systems, which also emit X-rays, has been successful. Astronomers found such a system in the constellation Cygnus, finding that at least one of the components has a mass exceeding the critical mass, i.e. more than two solar masses. The constellation Cygnus is best observed in summer and autumn, when it is visible directly overhead. The object was named Cygnus X-1, and is the first black hole candidate object. It is located 6,000 light-years from Earth and consists of two bodies: a normal giant star with a mass of about 20 suns and an invisible object with a mass of 10 suns that emits X-rays. But excuse me, you say, how can a black hole radiate if we just said that nothing can leave it! Yes, this is true, but the fact is that it is not the black hole itself that emits, but only the matter falling onto the black hole. It is by the radiation of the falling matter that we can assess the presence of a black hole.
Possessing powerful gravity, a black hole takes away part of the matter from its companion, as if sucking out matter, which spirals towards the black hole. The closer the extracted matter is to the black hole, the more it heats up and, finally, begins to emit in the X-ray range, which is detected by terrestrial radiation detectors. When reaching the vicinity of the gravitational radius (from where radiation can still escape), the gas heats up to 10 million degrees, and the X-ray luminosity of this gas is thousands of times greater than the luminosity of the Sun in all ranges! Flashes of radiation are visible no less than 200 kilometers from the center of the black hole, and its actual size is about 30 kilometers. So, black holes exist, and in fact they are an extremely compressed region of space-time (for simplicity, a super-dense ball), which no radiation can leave. It should be noted that due to the unusual nature of black holes, the media speculate on their ability to absorb surrounding matter. Having passed near the Earth, a black hole may well change the shape of the Earth with its gravity and begin to pull its matter inside itself. But such an event is extremely unlikely, especially since, as was said, the closest of them are located at a distance of several thousand light years. Therefore, even if we assume that a black hole suddenly heads towards the Earth, it will be able to reach it only after several thousand years, and this despite the fact that it will move at the speed of light. In this case, the condition of exact orientation towards the Earth must be observed, which at such a distance loses all meaning. Therefore, with full confidence we can say that humanity is not threatened with death from a black hole... When talking about black holes, we always talked about an external observer, i.e. tried to detect a black hole from the outside.
And what will happen to the observer if he suddenly finds himself on the other side of the gravitational radius, otherwise called the event horizon. This is where it all begins amazing property black holes. It’s not for nothing that when talking about black holes, we always mentioned time, or more precisely space-time. According to Einstein's theory of relativity, the faster a body moves, the greater its mass becomes, but the slower time begins to pass! At low speeds under normal conditions this effect is not noticeable, but if the body ( spaceship) 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! Strict mathematical formulas speak about this. Let's return to the black hole. Let's imagine a fantastic situation when a starship with astronauts on board approaches the gravitational radius or event horizon. It is clear that the event horizon is so named because we can observe any events (observe anything at all) only up to this boundary. That we are not able to observe beyond this border. However, being inside a ship approaching a black hole, the astronauts will feel the same as before, because... According to their watch, 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 spacecraft will reach the center of the black hole literally in an instant.
And for an external observer, the spacecraft will simply stop at the event horizon, and will remain there almost forever! This is the paradox of the colossal gravity of black holes. The natural question is whether the astronauts who are going into infinity according to the clock of an external observer will remain alive. No. And the point is not at all in enormous gravity, but in tidal forces, which for such a small and massive body change greatly over short distances. With an astronaut's height of 1 m 70 cm, the tidal forces at his head will be much less than at his feet and he will simply be torn apart already at the event horizon. So we're in general outline found out what black holes are, but so far we were talking about stellar-mass black holes. Currently, astronomers have discovered supermassive black holes whose mass may be a billion suns! Supermassive black holes are no different 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. At 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 conducted a global search for supermassive black holes, which, according to modern theoretical calculations, should be located at the center of every galaxy.
Modern technologies make it possible to detect the presence of these collapsars in neighboring galaxies, but very few of them have been discovered. This means that either black holes are simply hidden 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 onto them, and to make a census of such sources, satellites with X-ray telescopes on board were launched into near-Earth cosmic space. While searching for sources of X-rays, the Chandra and Rossi space observatories discovered that the sky was filled with background X-ray radiation that was millions of times brighter than visible radiation. Much of this background X-ray emission from the sky must come from black holes. Usually in astronomy there are three types of black holes. The first is black holes of stellar masses (about 10 solar masses). They form from massive stars when they run out of thermonuclear fuel. The second is supermassive black holes in the centers of galaxies (millions to billions of solar masses). And finally, the primary black holes, formed at the beginning of the life of the Universe, whose masses are small (on 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? Filling space with X-rays, they, however, do not want to show their true “face”. But in order to build a clear theory of the connection between background X-ray radiation and black holes, it is necessary to know their number. At the moment, space telescopes have only been able to detect Not a large number of supermassive black holes, the existence of which can be considered proven. Indirect signs make it possible to increase the number of observed black holes responsible for background radiation to 15%. We have to assume that the remaining supermassive black holes are simply hiding behind thick layers of dust clouds that transmit only high-energy X-rays or are too far away to be detected modern means observations.
Supermassive black hole (surroundings) at the center of the M87 galaxy (X-ray image). The ejection (jet) from the event horizon is visible. Image from www.college.ru/astronomy
Finding hidden black holes is one of the main tasks of modern X-ray astronomy. Recent breakthroughs in this area, associated with research using the Chandra and Rossi telescopes, however, cover only the low-energy X-ray range - approximately 2000-20,000 electron volts (for comparison, the energy of optical radiation is about 2 electrons). volt). Significant amendments to these studies can be made by the European space telescope Integral, which is capable of penetrating into the still insufficiently studied region of X-ray radiation with an energy 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 has low energy, multiple peaks (points) of radiation with an energy of about 30,000 electron-volts appear against this background. Scientists are still lifting the lid on what produces these peaks, and Integral is the first telescope sensitive enough to detect such X-ray sources. According to astronomers, high-energy rays generate so-called Compton-thick objects, that is, supermassive black holes shrouded in a dust shell. It is Compton objects that are responsible for X-ray peaks of 30,000 electron volts in the background radiation field.
But, continuing their 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 for further development theories. So, the missing X-rays are not supplied by Compton-thick, but by ordinary supermassive black holes? Then what about dust curtains for low-energy X-rays? The answer seems to lie in the fact that many black holes (Compton objects) had enough time to absorb all the gas and dust that enveloped them, but before that they had the opportunity to make themselves known with high-energy X-rays. After consuming all the matter, such black holes were no longer capable of generating X-rays at 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 them, since although the black hole no longer emits, the radiation it previously created continues to travel through the Universe. However, it is possible that the missing black holes are more hidden than astronomers realize, meaning that just because we don't see them doesn't mean they aren't there. We just don’t have enough observational power yet to see them. Meanwhile, NASA scientists plan to expand the search for hidden black holes even further into the Universe. This is where the underwater part of the iceberg is located, they believe. Over the course of several months, research will be carried out as part of the Swift mission. Penetrating into the deep Universe will reveal hidden black holes, find the missing link to background radiation, and shed light on their activity in the early era of the Universe.
ADDITION
Counting black holes has begun
The sky in gamma rays (dots indicate sources of gamma radiation). Image from http://www.esa.int/
The largest of the black holes are supermassive ones, which are millions to billions of times the mass of the Sun, and each of them is located at the center of most galaxies. These gravitational monsters have a huge “appetite”. Increasingly increasing their mass, they have already absorbed the surrounding matter to the “sum” of millions of Suns, but have not yet been saturated, continuing their formation further. The permanent menu of a black hole includes: gas, dust, planets and stars, but sometimes adherents of the collapse allow themselves to feast on “delicacies”. For dessert, black holes prefer compact massive objects, such as stellar-mass black holes, neutron stars and white dwarfs that accidentally fall into the gravitational field of a supermassive object. It is these objects that emit the loudest screams into the Universe in the X-ray and gamma-ray range when the black hole “feasts” on them. It would seem that it is enough to launch a space telescope with gamma-ray detectors into orbit and begin a successful search for gamma-ray bursts from black holes, thus rewriting all such objects. For these purposes, at the end of 2002, the Integral satellite of the ESA space agency, capable of viewing the sky in the gamma range, was launched into orbit. But here, too, the Universe forces scientists to wade through thorns.
Since the entire sky is filled with background gamma-ray radiation, this makes it difficult to detect faint gamma-ray bursts from very distant sources, thus underestimating the actual number of black holes, which affects the validity of cosmological theories. To get around this obstacle, an international team including Russian scientists Evgeniy Churazov and Rashid Sunyaev from the Space Research Institute proposed calibrating Integral's instruments to take into account the level of background gamma radiation. To do this, they decided to direct the Integral radiation receivers towards the Earth, which “with its body” would cover the general background of the sky. This event was very risky due to the brightness of the Earth for Intregal devices operating in the optical range. The optics of the space observatory could “blind”, because... tuned to distant space, which is several orders of magnitude fainter than the nearby planet. But scientists conducted the experiment without “losses”, and the risk was justified. Using a natural radiation shield, astronomers measured the level of incoming radiation and compared the resulting observational records with earlier ones. This made it possible to find the “zero” point of radiation, from which the reading will now be made when analyzing the new data obtained. Thus, by excluding the general gamma-ray background, researchers will be able to more accurately identify the location of black holes, clarifying their number and distribution in space. Before the launch of Integral, only a few dozen objects were observed in the gamma ray range. To date, with the help of this space telescope it has been possible to find 300 individual sources in our Galaxy and about 100 of the “brightest” black holes in other galaxies. But this is just the tip of the iceberg. Astronomers are confident that there are tens of millions of black holes, the radiation from which merges with the background. All of them will have to be discovered by Intergral, which will make it possible to establish ideal order in cosmological theories.
Interesting facts from the life of black holes
An artist's impression of a star being swallowed up by a black hole. Image: NASA/JPL
Some black holes are thought to be more active than their quiet neighbors. Active black holes absorb the surrounding matter, and if a “unwary” star flying by gets caught in the flight of gravity, it will certainly be “eaten” in the most barbaric way (torn to shreds). The absorbed material, falling into a black hole, is heated to enormous temperatures and experiences a flare in the gamma, x-ray and ultraviolet range. There is also a supermassive black hole at the center of the Milky Way, but it is more difficult to study than holes in neighboring or even distant galaxies. This is due to the 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 black hole activity are much more effective in those galaxies whose cores are clearly visible. While observing one of the distant galaxies, located in the constellation Boötes at a distance of 4 billion light years, astronomers were for the first time able to track from the beginning to almost the end the process of absorption of a star by a supermassive black hole. For thousands of years, this giant collapsar rested quietly and peacefully in the center of an unnamed elliptical galaxy, until one of the stars dared to get close enough to it.
The powerful gravity of the black hole tore the star apart. Clots of matter began to fall onto the black hole and, upon reaching the event horizon, flared brightly in the ultraviolet range. These flares were recorded by NASA's new Galaxy Evolution Explorer space telescope, which studies the sky in ultraviolet light. The telescope continues to observe the behavior of the distinguished object today, because The black hole's meal has not yet ended, 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 together with their host galaxies (or, conversely, galaxies evolve with a parent black hole). Earlier observations indicate that such excesses are not uncommon in the Universe. Scientists have calculated that, on average, a star is consumed by a supermassive black hole in 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.
Multimedia video on the topic. Black holes, jets and quasars, movie file (mov, 8.3Mb, 71 sec) Black holes are so dense and heavy that nothing - not even light - can escape from it. These objects are very mysterious. Black holes can consume surrounding gas and stars. They are found at the centers of galaxies and quasars and can create powerful, high-energy jets from the spiraling disks that surround them. This video shows some observations of black holes, jets and quasars. Schematic representation of a black hole (35.2Kb, photo)
Black holes are perhaps the most mysterious and enigmatic astronomical objects in our Universe; since their discovery, they have attracted the attention of scientists and excite the imagination of science fiction writers. What are black holes and what do they represent? Black holes are extinct stars, due to their physical characteristics, which have such high density and such powerful gravity that even light cannot escape beyond them.
History of the discovery of black holes
For the first time, the theoretical existence of black holes, long before their actual discovery, was suggested by a certain D. Michel (an English priest from Yorkshire, who is interested in astronomy in his spare time) back in 1783. According to his calculations, if we take ours and compress it (in modern computer language, archive it) to a radius of 3 km, such a large (simply enormous) gravitational force will be formed that even light will not be able to leave it. This is how the concept of a “black hole” appeared, although in fact it is not black at all; in our opinion, the term “dark hole” would be more appropriate, because it is precisely the absence of light that occurs.
Later, in 1918, the great scientist Albert Einstein wrote about the issue of black holes in the context of the theory of relativity. But it was only in 1967, through the efforts of the American astrophysicist John Wheeler, that the concept of black holes finally won a place in academic circles.
Be that as it may, D. Michel, Albert Einstein, and John Wheeler in their works assumed only the theoretical existence of these mysterious celestial objects in outer space, but the real discovery of black holes took place in 1971, it was then that they were first noticed in telescope.
This is what a black hole looks like.
How black holes form in space
As we know from astrophysics, all stars (including our Sun) have some limited supply of fuel. And although the life of a star can last billions of light years, sooner or later this conditional supply of fuel comes to an end, and the star “goes out”. The process of “fading” of a star is accompanied by intense reactions, during which the star undergoes a significant transformation and, depending on its size, can turn into a white dwarf, a neutron star or a black hole. Moreover, the largest stars, with incredibly impressive sizes, usually turn into a black hole - due to the compression of these most incredible sizes, there is a multiple increase in the mass and gravitational force of the newly formed black hole, which turns into a kind of galactic vacuum cleaner - absorbing everything and everyone around it.
A black hole swallows a star.
A small note - our Sun, by galactic standards, is not at all a large star and after its extinction, which will occur in about a few billion years, it most likely will not turn into a black hole.
But let's be honest with you - today, scientists do not yet know all the intricacies of the formation of a black hole; undoubtedly, this is an extremely complex astrophysical process, which in itself can last millions of light years. Although it is possible to advance in this direction could be the discovery and subsequent study of the so-called intermediate black holes, that is, stars in a state of extinction, in which the active process of black hole formation is taking place. By the way, a similar star was discovered by astronomers in 2014 in the arm of a spiral galaxy.
How many black holes are there in the Universe?
According to the theories of modern scientists, there may be up to hundreds of millions of black holes in our Milky Way galaxy. There may be no less of them in our neighboring galaxy, to which there is nothing to fly from our Milky Way - 2.5 million light years.
Black hole theory
Despite the enormous mass (which is hundreds of thousands of times greater than the mass of our Sun) and the incredible strength of gravity, it was not easy to see black holes through a telescope, because they do not emit light at all. Scientists managed to notice the black hole only at the moment of its “meal” - absorption of another star, at this moment characteristic radiation appears, which can already be observed. Thus, the black hole theory has found actual confirmation.
Properties of black holes
The main property of a black hole is its incredible gravitational fields, which do not allow the surrounding space and time to remain in their usual state. Yes, you heard right, time inside a black hole passes many times slower than usual, and if you were there, then when you returned back (if you were so lucky, of course), you would be surprised to notice that centuries have passed on Earth, and you haven’t even grown old made it in time. Although let’s be truthful, if you were inside a black hole, you would hardly survive, since the force of gravity there is such that any material object would simply be torn apart, not even into pieces, into atoms.
But if you were even close to a black hole, within the influence of its gravitational field, you would also have a hard time, since the more you resist its gravity, trying to fly away, the faster you would fall into it. The reason for this seemingly paradox is the gravitational vortex field that all black holes possess.
What if a person falls into a black hole
Evaporation of black holes
English astronomer S. Hawking discovered interesting fact: Black holes also appear to emit evaporation. True, this only applies to holes of relatively small mass. The powerful gravity around them gives birth to pairs of particles and antiparticles, one of the pair is pulled in by the hole, and the second is expelled out. Thus, the black hole emits hard antiparticles and gamma-rays. This evaporation or radiation from a black hole was named after the scientist who discovered it - “Hawking radiation”.
The largest black hole
According to the black hole theory, at the center of almost all galaxies there are huge black holes with masses from several million to several billion solar masses. And relatively recently, scientists discovered the two largest black holes known today; they are located in two nearby galaxies: NGC 3842 and NGC 4849.
NGC 3842 is the brightest galaxy in the constellation Leo, located 320 million light years away from us. At its center there is a huge black hole weighing 9.7 billion solar masses.
NGC 4849, a galaxy in the Coma cluster, 335 million light-years away, boasts an equally impressive black hole.
The gravitational field of these giant black holes, or in academic terms, their event horizon, is approximately 5 times the distance from the Sun to ! Such a black hole would eat our solar system and I wouldn’t even choke.
The smallest black hole
But in the vast family of black holes there are also very small representatives. So the most dwarf black hole discovered by scientists at currently its mass is only 3 times greater than the mass of our Sun. In fact, this is the theoretical minimum required for the formation of a black hole; if that star were slightly smaller, the hole would not have formed.
Black holes are cannibals
Yes, there is such a phenomenon, as we wrote above, black holes are a kind of “galactic vacuum cleaners” that absorb everything around them, including... other black holes. Recently, astronomers discovered that a black hole from one galaxy was being eaten by an even larger black glutton from another galaxy.
- According to the hypotheses of some scientists, black holes are not only galactic vacuum cleaners that suck everything into themselves, but under certain circumstances they can themselves give birth to new universes.
- Black holes can evaporate over time. We wrote above that the English scientist Stephen Hawking discovered that black holes have the property of radiation and after some very long period of time, when there is nothing left to absorb around, the black hole will begin to evaporate more, until over time it gives up all its mass into surrounding space. Although this is only an assumption, a hypothesis.
- Black holes slow down time and bend space. We have already written about time dilation, but space under the conditions of a black hole will also be completely curved.
- Black holes limit the number of stars in the Universe. Namely, their gravitational fields prevent the cooling of gas clouds in space, from which, as is known, new stars are born.
Black holes on the Discovery Channel, video
And in conclusion, we offer you an interesting scientific documentary about black holes from the Discovery Channel