Black holes are one of the strangest phenomena in the universe. In any case, at this stage of human development. This is an object with infinite mass and density, and hence attraction, beyond which even light cannot escape - therefore, the hole is black. A supermassive black hole can suck in an entire galaxy and not choke, and beyond the event horizon, our familiar physics begins to screech and twist into a knot. On the other hand, black holes can become potential transition "holes" from one space node to another. The question is, how close can we get to the black hole, and will it be fraught with consequences?

The supermassive black hole Sagittarius A *, located in the center of our galaxy, not only sucks in nearby objects, but also emits powerful radio waves. Scientists have long tried to make out these rays, but they were hampered by the diffused light surrounding the hole. Finally, they were able to break through the light noise using 13 telescopes, which combined into a single powerful system. Subsequently, they discovered interesting information about previously mysterious rays.

A few days ago, on March 14, one of the most outstanding physicists of our time left this world,

Every person who gets acquainted with astronomy sooner or later experiences a strong curiosity about the most mysterious objects of the Universe - black holes. These are the real masters of darkness, capable of "swallowing" any passing nearby atom and not letting even the light escape - their attraction is so powerful. These objects present a real challenge for physicists and astronomers. The former still cannot understand what is happening with the substance that has fallen into the black hole, and the latter, although they explain the most energy-consuming phenomena of space by the existence of black holes, have never had the opportunity to observe any of them directly. We will tell you about these most interesting celestial objects, find out what has already been discovered and what remains to be learned in order to lift the veil of secrecy.

What is a black hole?

The name "black hole" (in English - black hole) was proposed in 1967 by the American theoretical physicist John Archibald Wheeler (see photo on the left). It served to designate a celestial body, the attraction of which is so strong that it does not even let the light go from itself. That is why it is "black" because it does not emit light.

Indirect observations

This is the reason for this mystery: since black holes do not glow, we cannot see them directly and are forced to search and study them, using only indirect evidence that their existence leaves in the surrounding space. In other words, if a black hole engulfs a star, we do not see the black hole, but we can observe the devastating effects of its powerful gravitational field.

Laplace's intuition

Despite the fact that the expression "black hole" to denote the hypothetical final stage of the evolution of a star that collapsed into itself under the influence of gravity appeared relatively recently, the idea of ​​the possibility of the existence of such bodies arose more than two centuries ago. The Englishman John Michell and the Frenchman Pierre-Simon de Laplace independently put forward the hypothesis of the existence of "invisible stars"; while they were based on the usual laws of dynamics and Newton's law of universal gravitation. Today black holes have received their correct description based on Einstein's general theory of relativity.

In his work "Exposition of the system of the world" (1796) Laplace wrote: "A bright star of the same density as the Earth, with a diameter of 250 times the diameter of the Sun, due to its gravitational attraction, would not allow light rays to reach us. Therefore, it is possible that the largest and brightest celestial bodies for this reason are invisible. "

Invincible gravity

Laplace's idea was based on the concept of escape velocity (second cosmic velocity). A black hole is such a dense object that its attraction is capable of holding back even light, which develops the highest speed in nature (almost 300,000 km / s). In practice, it takes a speed higher than the speed of light to escape from a black hole, but this is not possible!

This means that a star of this kind will be invisible, since even light will not be able to overcome its powerful gravity. Einstein explained this fact through the phenomenon of deflection of light under the influence of a gravitational field. In reality, near the black hole, space-time is so curved that the trajectories of light rays are also closed on themselves. In order to turn the Sun into a black hole, we will have to concentrate all of its mass in a ball with a radius of 3 km, and the Earth will have to turn into a ball with a radius of 9 mm!

Types of black holes

About ten years ago, observations made it possible to assume the existence of two types of black holes: stellar, the mass of which is comparable to the mass of the Sun or slightly exceeds it, and supermassive, the mass of which ranges from several hundred thousand to many millions of solar masses. However, relatively recently, X-ray images and high-resolution spectra obtained from artificial satellites such as Chandra and HMM-Newton brought to the fore a third type of black hole - with an average mass thousands of times greater than the mass of the Sun.

Stellar black holes

Stellar black holes became known earlier than others. They are formed when a star of large mass at the end of its evolutionary path runs out of nuclear fuel and collapses into itself due to its own gravity. A stunning star explosion (known as a "supernova explosion") has catastrophic consequences: if the core of a star is more than 10 times the mass of the Sun, no nuclear force can withstand the gravitational collapse that will result in the appearance of a black hole.

Supermassive black holes

Supermassive black holes, first noted in the cores of some active galaxies, have a different origin. There are several hypotheses regarding their birth: a stellar black hole, which devours all the surrounding stars for millions of years; a merged cluster of black holes; a colossal cloud of gas collapsing directly into a black hole. These black holes are some of the most energetic objects in space. They are located in the centers of many, if not all, galaxies. Our Galaxy also has such a black hole. Sometimes, due to the presence of such a black hole, the nuclei of these galaxies become very bright. Galaxies with black holes in the center, surrounded by a large amount of falling matter and, therefore, capable of producing colossal amounts of energy, are called "active", and their nuclei - "active galactic nuclei" (AGN). For example, quasars (the most distant space objects available to our observation) are active galaxies, in which we see only a very bright core.

Medium and mini

Another mystery remains medium-mass black holes, which, according to recent studies, may be in the center of some globular clusters, such as M13 and NCC 6388. Many astronomers are skeptical about these objects, but some recent research suggests the presence of black holes medium in size even near the center of our Galaxy. English physicist Stephen Hawking also put forward a theoretical assumption about the existence of a fourth type of black hole - a "mini-hole" with a mass of only a billion tons (which is approximately equal to the mass of a large mountain). We are talking about primary objects, that is, those that appeared in the first moments of the life of the Universe, when the pressure was still very high. However, not a single trace of their existence has yet been found.

How to find a black hole

Just a few years ago, a light came on over black holes. Thanks to constantly improving instruments and technologies (both ground-based and space-based), these objects are becoming less and less mysterious; more precisely, the space around them becomes less mysterious. Indeed, since the black hole itself is invisible, we can only recognize it if it is surrounded by a sufficient amount of matter (stars and hot gas) orbiting around it at a short distance.

Watching binary systems

Some stellar black holes have been discovered while observing the orbital motion of a star around an invisible binary companion. Close binary systems (that is, consisting of two stars very close to each other), one of the companions in which is invisible, are a favorite object of observations of astrophysicists looking for black holes.

An indication of the presence of a black hole (or neutron star) is the strong emission of X-rays caused by a complex mechanism that can be schematically described as follows. Thanks to its powerful gravity, a black hole can pluck matter from a companion star; this gas is distributed in the form of a flat disk and spirals into the black hole. Friction resulting from the collision of particles of the falling gas heats the inner layers of the disk to several million degrees, which causes powerful X-rays to be emitted.

X-ray observations

For decades, X-ray observations of objects in our Galaxy and neighboring galaxies have made it possible to detect compact binary sources, about a dozen of which are systems containing black hole candidates. The main problem is to determine the mass of an invisible celestial body. The value of mass (albeit not very accurate) can be found by studying the movement of the companion or, much more difficult, by measuring the intensity of the X-ray radiation of the incident material. This intensity is related by the equation to the mass of the body on which this substance falls.

Nobel laureate

Something similar can be said for the supermassive black holes observed in the cores of many galaxies, the masses of which are estimated by measuring the orbital velocities of gas falling into the black hole. In this case, the rapid increase in the velocity of gas clouds orbiting in the center of galaxies, caused by the powerful gravitational field of a very large object, is revealed by observations in the radio range, as well as in optical rays. X-ray observations can confirm the increased release of energy caused by the fall of matter into the black hole. In the early 1960s, research in X-rays was begun by Riccardo Giaconi, an Italian working in the United States. The Nobel Prize awarded to him in 2002 recognized his "pioneering contributions to astrophysics that led to the discovery of X-ray sources in space."

Swan X-1: first candidate

Our Galaxy is not immune to the presence of objects-candidates for black holes. Fortunately, none of these objects are close enough to us to pose a threat to the existence of the Earth or the solar system. Despite the large number of noted compact X-ray sources (and these are the most likely candidates for finding black holes there), we are not sure that they actually contain black holes. The only one among these sources that does not have an alternative version is the close binary system Cygnus X-1, that is, the brightest X-ray source in the constellation Cygnus.

Massive stars

This system, with an orbital period of 5.6 days, consists of a very bright blue star of large size (its diameter is 20 times the solar one, and its mass is about 30 times), easily distinguishable even in your telescope, and an invisible second star, the mass which is estimated at several solar masses (up to 10). Located 6500 light-years away, the second star would be perfectly visible if it were an ordinary star. Its invisibility, powerful X-rays emitted by the system, and finally its mass estimate lead most astronomers to think that this is the first confirmed case of a stellar black hole.

Doubts

However, there are also skeptics. Among them is one of the largest researchers of black holes, physicist Stephen Hawking. He even made a bet with his American counterpart Keel Thorne, an ardent advocate of classifying Cygnus X-1 as a black hole.

The dispute over the nature of the object Swan X-1 is not Hawking's only bet. Having devoted several nine years to theoretical studies of black holes, he became convinced of the erroneousness of his previous ideas about these mysterious objects .. In particular, Hawking assumed that after falling into a black hole, matter disappears forever, and with it all his information baggage disappears. He was so sure of this that in 1997 he entered into a bet on this topic with his American colleague John Preskill.

Admitting a mistake

On July 21, 2004, Hawking admitted Preskill was right in his speech at the Congress on the Theory of Relativity in Dublin. Black holes do not lead to the complete disappearance of matter. Moreover, they have a certain kind of "memory". They may well contain traces of what they have absorbed. Thus, by "evaporating" (that is, slowly emitting radiation due to the quantum effect), they can return this information to our Universe.

Black holes in the Galaxy

Astronomers still harbor many doubts about the presence of stellar black holes in our Galaxy (such as the one belonging to the Cygnus X-1 binary); but there is much less doubt about supermassive black holes.

In the center

There is at least one supermassive black hole in our Galaxy. Its source, known as Sagittarius A *, is precisely located in the center of the plane of the Milky Way. Its name is due to the fact that it is the most powerful radio source in the constellation Sagittarius. It is in this direction that both the geometric and physical centers of our galactic system are located. At a distance of about 26,000 light-years from us, a supermassive black hole associated with the source of radio waves Sagittarius A * has a mass that is estimated at about 4 million solar masses, enclosed in space, the volume of which is comparable to the volume of the solar system. Its relative proximity to us (this supermassive black hole is undoubtedly the closest to Earth) has become the reason that in recent years the object has undergone a particularly deep study using the Chandra space observatory. It turned out, in particular, that it is also a powerful source of X-ray radiation (but not as powerful as sources in active galactic nuclei). Sagittarius A * is possibly the "dormant" remnant of what millions or billions of years ago was the active core of our Galaxy.

Second black hole?

However, some astronomers believe that there is another surprise in our Galaxy. This is a second medium-mass black hole that holds together a cluster of young stars and prevents them from falling into a supermassive black hole located in the center of the Galaxy itself. How can it be that at a distance of less than one light-year from it there could be a star cluster aged just 10 million years, that is, by astronomical standards, very young? According to the researchers, the answer is that the cluster was born in the wrong place (the environment around the central black hole is too hostile for star formation), but was "pulled" there due to the existence of a second black hole inside it, which has a mass of average values.

In orbit

The individual stars of the cluster, attracted by the supermassive black hole, began to shift towards the galactic center. However, instead of being dispersed in space, they remain clumped together thanks to the gravitational pull of a second black hole located in the center of the cluster. The mass of this black hole can be estimated based on its ability to "leash" an entire star cluster. A medium-sized black hole appears to orbit the central black hole in about 100 years. This means that continuous observation over many years will allow us to "see" it.

Due to the relatively recent increase in interest in making popular science films on the topic of space exploration, the modern viewer has heard a lot about such phenomena as the singularity, or black hole. However, movies, obviously, do not reveal the entire nature of these phenomena, and sometimes even distort the constructed scientific theories for greater effectiveness. For this reason, the idea of ​​many modern people about these phenomena is either completely superficial or completely erroneous. One of the solutions to the problem is this article, in which we will try to understand the existing research results and answer the question - what is a black hole?

In 1784, the English priest and naturalist John Michell first mentioned in a letter to the Royal Society some hypothetical massive body that has such a strong gravitational attraction that the second cosmic speed for it will exceed the speed of light. The second cosmic speed is the speed that a relatively small object will need to overcome the gravitational attraction of a celestial body and go beyond the closed orbit around this body. According to his calculations, a body with the density of the Sun and a radius of 500 solar radii will have on its surface a second cosmic speed equal to the speed of light. In this case, even the light will not leave the surface of such a body, and therefore this body will only absorb the incoming light and remain invisible to the observer - a kind of black spot against the background of dark space.

However, Michell's concept of a supermassive body did not attract much interest, until the work of Einstein. Let us recall that the latter defined the speed of light as the limiting speed of information transmission. In addition, Einstein expanded the theory of gravitation for speeds close to the speed of light (). As a result, it was no longer relevant to apply Newtonian theory to black holes.

Einstein's equation

As a result of the application of general relativity to black holes and the solution of Einstein's equations, the main parameters of a black hole were identified, of which there are only three: mass, electric charge and angular momentum. It should be noted the significant contribution of the Indian astrophysicist Subramanian Chandrasekhar, who created the fundamental monograph: "The Mathematical Theory of Black Holes."

Thus, the solution to Einstein's equations is presented by four options for four possible types of black holes:

• BH without rotation and without charge - Schwarzschild's solution. One of the first descriptions of a black hole (1916) using Einstein's equations, but without taking into account two of the three body parameters. The solution of the German physicist Karl Schwarzschild makes it possible to calculate the external gravitational field of a spherical massive body. The peculiarity of the concept of BH by the German scientist is the presence of an event horizon and the one hidden behind it. Also, Schwarzschild first calculated the gravitational radius, which received his name, which determines the radius of the sphere on which the event horizon for a body with a given mass would be located.
• BH without rotation with charge - Reisner-Nordström solution. A solution put forward in 1916-1918, taking into account the possible electric charge of the black hole. This charge cannot be arbitrarily large and is limited due to the resulting electrical repulsion. The latter should be compensated by gravitational attraction.
• BH with rotation and without charge - Kerr's solution (1963). A rotating Kerr black hole differs from a static one by the presence of the so-called ergosphere (read about this and other components of the black hole below).
• BH with rotation and charge - Kerr - Newman solution. This solution was calculated in 1965 and is currently the most complete, since it takes into account all three BH parameters. However, it is still assumed that in nature black holes have an insignificant charge.

Black hole formation

There are several theories about how a black hole forms and appears, the most famous of which is the formation of a star with sufficient mass as a result of gravitational collapse. This compression can end the evolution of stars with a mass of more than three solar masses. Upon completion of thermonuclear reactions inside such stars, they begin to rapidly collapse into superdense. If the gas pressure of the neutron star cannot compensate for the gravitational forces, that is, the mass of the star overcomes the so-called. the Oppenheimer-Volkov limit, then the collapse continues, with the result that matter is compressed into a black hole.

The second scenario, describing the birth of a black hole, is the compression of protogalactic gas, that is, interstellar gas that is at the stage of transformation into a galaxy or some kind of cluster. If there is insufficient internal pressure to compensate for the same gravitational forces, a black hole can arise.

Two other scenarios remain hypothetical:

• The occurrence of BH as a result - the so-called. primordial black holes.
• Occurrence as a result of nuclear reactions at high energies. An example of such reactions is collider experiments.

Structure and physics of black holes

The Schwarzschild structure of a black hole includes only two elements, which were mentioned earlier: the singularity and the event horizon of the black hole. Briefly speaking about the singularity, it can be noted that it is impossible to draw a straight line through it, and also that within it most of the existing physical theories do not work. Thus, the physics of the singularity remains a mystery to scientists today. a black hole is a kind of border, crossing which, a physical object loses the ability to return back beyond its limits and will definitely "fall" into the singularity of the black hole.

The structure of a black hole becomes somewhat more complicated in the case of the Kerr solution, namely, in the presence of rotation of the BH. Kerr's solution assumes that the hole has an ergosphere. The ergosphere is a certain region outside the event horizon, inside which all bodies move in the direction of rotation of the black hole. This area is not yet exciting and it is possible to leave it, unlike the event horizon. The ergosphere is probably a kind of analogue of the accretion disk, which is rotating matter around massive bodies. If a static Schwarzschild black hole is represented as a black sphere, then the Kerry BH, due to the presence of the ergosphere, has the shape of an oblate ellipsoid, in the form of which we often saw BH in drawings, in old movies or video games.

• How much does a black hole weigh? - The greatest theoretical material on the origin of a black hole is available for the scenario of its appearance as a result of the collapse of a star. In this case, the maximum mass of a neutron star and the minimum mass of a black hole are determined by the Oppenheimer-Volkov limit, according to which the lower limit of the BH mass is 2.5 - 3 solar masses. The heaviest black hole ever discovered (in the galaxy NGC 4889) has a mass of 21 billion solar masses. However, one should not forget about BHs, hypothetically arising as a result of nuclear reactions at high energies, such as those at colliders. The mass of such quantum black holes, in other words, "Planck black holes", has an order of magnitude, namely 2 · 10 −5 g.
• The size of the black hole. The minimum BH radius can be calculated from the minimum mass (2.5 - 3 solar masses). If the gravitational radius of the Sun, that is, the area where the event horizon would be located, is about 2.95 km, then the minimum BH radius of 3 solar masses will be about nine kilometers. Such a relatively small size does not fit into the head when it comes to massive objects that attract everything around. However, for quantum black holes, the radius is - 10 −35 m.
• The average density of a black hole depends on two parameters: mass and radius. The density of a black hole with a mass of the order of three solar masses is about 6 · 10 26 kg / m³, while the density of water is 1000 kg / m³. However, such small black holes have not been found by scientists. Most of the detected BHs have a mass of more than 10 5 solar masses. There is an interesting pattern according to which the more massive a black hole, the lower its density. In this case, a change in mass by 11 orders of magnitude leads to a change in density by 22 orders of magnitude. Thus, a black hole with a mass of 1 · 10 9 solar masses has a density of 18.5 kg / m³, which is one unit less than the density of gold. And BHs with a mass of more than 10 10 solar masses can have an average density less than the density of air. Based on these calculations, it is logical to assume that the formation of a black hole occurs not due to the compression of matter, but as a result of the accumulation of a large amount of matter in a certain volume. In the case of quantum BHs, their density can be about 1094 kg / m³.
• The temperature of a black hole is also inversely proportional to its mass. This temperature is directly related to. The spectrum of this radiation coincides with the spectrum of an absolutely black body, that is, a body that absorbs all incident radiation. The radiation spectrum of an absolutely black body depends only on its temperature, then the BH temperature can be determined from the Hawking radiation spectrum. As mentioned above, the smaller the black hole, the more powerful this radiation is. In this case, Hawking radiation remains hypothetical, since it has not yet been observed by astronomers. It follows from this that if Hawking radiation exists, then the temperature of the observed BHs is so low that it does not allow registering the indicated radiation. According to calculations, even the temperature of a hole with a mass on the order of the mass of the Sun is negligible (1 · 10 -7 K or -272 ° C). The temperature of quantum black holes can reach about 10 12 K, and with their rapid evaporation (about 1.5 minutes), such BHs can emit energy of the order of ten million atomic bombs. But, fortunately, the creation of such hypothetical objects will require an energy 10 14 times greater than that achieved today at the Large Hadron Collider. In addition, such phenomena have never been observed by astronomers.

What does a black hole consist of?

Another question worries, both scientists and those who are simply fond of astrophysics - what does a black hole consist of? There is no unambiguous answer to this question, since it is not possible to look beyond the event horizon surrounding any black hole. In addition, as mentioned earlier, theoretical models of a black hole provide for only 3 of its components: the ergosphere, the event horizon and the singularity. It is logical to assume that in the ergosphere there are only those objects that were attracted by the black hole, and which now revolve around it - various kinds of cosmic bodies and cosmic gas. The event horizon is only a thin implicit border, after falling beyond which, the same cosmic bodies are irretrievably attracted towards the last main component of the BH - the singularity. The nature of the singularity has not been studied today and it is too early to talk about its composition.

According to some assumptions, the black hole may be composed of neutrons. If we follow the scenario of a black hole as a result of the contraction of a star to a neutron star with its subsequent contraction, then, probably, the main part of the black hole consists of neutrons, of which the neutron star itself consists. In simple words: when a star collapses, its atoms contract in such a way that electrons combine with protons, thereby forming neutrons. A similar reaction actually takes place in nature, while neutrino emission occurs with the formation of a neutron. However, these are only assumptions.

What happens if you fall into a black hole?

Falling into an astrophysical black hole stretches the body. Consider a hypothetical suicide astronaut walking into a black hole in nothing but a spacesuit, feet first. Crossing the event horizon, the astronaut will not notice any changes, despite the fact that he no longer has the opportunity to get out. At some point, the astronaut will reach a point (slightly behind the event horizon) at which deformation of his body will begin to occur. Since the gravitational field of a black hole is inhomogeneous and is represented by a force gradient increasing towards the center, the astronaut's legs will be subjected to a noticeably greater gravitational effect than, for example, the head. Then, due to gravity, or rather, tidal forces, the legs will "fall" faster. Thus, the body begins to gradually stretch in length. To describe this phenomenon, astrophysicists have come up with a rather creative term - spaghettification. Further stretching of the body is likely to decompose it into atoms, which, sooner or later, will reach a singularity. What a person will feel in this situation is anyone's guess. It is worth noting that the stretching effect of a body is inversely proportional to the mass of the black hole. That is, if a BH with a mass of three Suns instantly stretches / breaks the body, then the supermassive black hole will have lower tidal forces and, there are suggestions that some physical materials could “endure” such a deformation without losing their structure.

As you know, time flows more slowly near massive objects, which means that time for a suicide astronaut will flow much slower than for earthlings. In this case, perhaps he will outlive not only his friends, but also the Earth itself. Calculations will be required to determine how much time will slow down for the astronaut; however, from the above, it can be assumed that the astronaut will fall into the black hole very slowly and, perhaps, simply will not live to see the moment when his body begins to deform.

It is noteworthy that for an observer outside, all bodies that have flown up to the event horizon will remain at the edge of this horizon until their image disappears. The reason for this is the gravitational redshift. Simplifying somewhat, we can say that the light falling on the body of a suicide cosmonaut “frozen” at the event horizon will change its frequency due to its slowed down time. As time passes more slowly, the frequency of light will decrease and the wavelength will increase. As a result of this phenomenon, at the exit, that is, for an external observer, the light will gradually shift towards the low-frequency - red. A shift of light along the spectrum will take place, as the suicide astronaut moves further and further from the observer, albeit almost imperceptibly, and his time passes more and more slowly. Thus, the light reflected by his body will soon go beyond the visible spectrum (the image will disappear), and in the future the astronaut's body can be caught only in the infrared region, and later in the radio frequency, and as a result, the radiation will be completely elusive.

Despite the above, it is assumed that in very large supermassive black holes, tidal forces do not change so much with distance and act almost uniformly on the falling body. In this case, the falling spaceship would retain its structure. A reasonable question arises - where does the black hole lead? This question can be answered by the work of some scientists, linking two such phenomena as wormholes and black holes.

Back in 1935, Albert Einstein and Nathan Rosen, taking into account, put forward a hypothesis about the existence of so-called wormholes, connecting two points of space-time by a path in places of significant curvature of the latter - the Einstein-Rosen bridge or a wormhole. For such a powerful curvature of space, bodies with a gigantic mass will be required, with the role of which black holes would perfectly cope.

The Einstein-Rosen Bridge is considered an impassable wormhole because it is small and unstable.

A traversable wormhole is possible within the framework of the theory of black and white holes. Where the white hole is the output of information trapped in a black hole. The white hole is described in the framework of general relativity, but today it remains hypothetical and has not been discovered. Another model of a wormhole, proposed by American scientists Kip Thorne and his graduate student, Mike Morris, can be walkable. However, as in the case of the Morris-Thorne wormhole, and in the case of black and white holes, the possibility of travel requires the existence of so-called exotic matter, which has negative energy and also remains hypothetical.

Black holes in the universe

The existence of black holes was confirmed relatively recently (September 2015); however, up to that time, there was already considerable theoretical material on the nature of BHs, as well as many candidate objects for the role of a black hole. First of all, the size of the BH should be taken into account, since the very nature of the phenomenon depends on them:

• Stellar mass black hole... Such objects are formed as a result of the collapse of a star. As mentioned earlier, the minimum mass of a body capable of forming such a black hole is 2.5 - 3 solar masses.
• Medium-mass black holes... A conditional intermediate type of black holes that have increased due to the absorption of nearby objects, such as a gas accumulation, a nearby star (in two-star systems) and other cosmic bodies.
• Supermassive black hole... Compact objects with 10 5 -10 10 solar masses. The distinctive properties of such BHs are the paradoxically low density, as well as the weak tidal forces, which were mentioned earlier. It is such a supermassive black hole at the center of our Milky Way galaxy (Sagittarius A *, Sgr A *), as well as most other galaxies.

Candidates for the Black House

The nearest black hole, or rather a candidate for the role of a BH, is an object (V616 Unicorn), which is located at a distance of 3000 light years from the Sun (in our galaxy). It consists of two components: a star with a mass of half the solar mass, as well as an invisible small body, the mass of which is 3 - 5 solar masses. If this object turns out to be a small black hole of stellar mass, then by right it will be the nearest BH.

Following this object, the second closest black hole is the Cyg X-1 object, which was the first candidate for the role of a BH. The distance to it is approximately 6070 light years. It is well studied: it has a mass of 14.8 solar masses and an event horizon radius of about 26 km.

According to some sources, another closest candidate for the role of a BH may be a body in the star system V4641 Sagittarii (V4641 Sgr), which, according to 1999 estimates, was located at a distance of 1600 light years. However, subsequent studies increased this distance by at least 15 times.

How many black holes are there in our galaxy?

There is no exact answer to this question, since it is rather difficult to observe them, and for the entire time of the study of the sky, scientists have managed to find about a dozen black holes within the Milky Way. Without indulging in calculations, we note that there are about 100 - 400 billion stars in our galaxy, and about every thousandth star has enough mass to form a black hole. It is likely that millions of black holes could have formed during the existence of the Milky Way. Since it is easier to register huge black holes, it is logical to assume that most of the BHs in our galaxy are most likely not supermassive. It is noteworthy that the 2005 NASA studies suggest the presence of a swarm of black holes (10-20 thousand) orbiting the center of the galaxy. In addition, in 2016, Japanese astrophysicists discovered a massive satellite near the object * - a black hole, the core of the Milky Way. Due to the small radius (0.15 light years) of this body, as well as its huge mass (100,000 solar masses), scientists suggest that this object is also a supermassive black hole.

The core of our galaxy, the black hole of the Milky Way (Sagittarius A *, Sgr A * or Sagittarius A *) is supermassive and has a mass of 4.31 10 6 solar masses, and a radius of 0.00071 light years (6.25 light years . or 6.75 billion km). The temperature of Sagittarius A * together with the cluster around it is about 1 · 10 7 K.

The largest black hole

The largest black hole in the Universe that scientists have discovered is a supermassive black hole, FSRQ blazar, in the center of galaxy S5 0014 + 81, at a distance of 1.2 · 10 10 light years from Earth. According to preliminary results of observation, using the Swift space observatory, the mass of the BH was 40 billion (40 · 10 9) solar masses, and the Schwarzschild radius of such a hole was 118.35 billion kilometers (0.013 light years). It is also estimated to have originated 12.1 billion years ago (1.6 billion years after the Big Bang). If this giant black hole does not absorb the surrounding matter, then it will survive to the era of black holes - one of the epochs of the development of the Universe, during which black holes will dominate in it. If the nucleus of the galaxy S5 0014 + 81 continues to grow, then it will become one of the last black holes that will exist in the Universe.

The other two known black holes, although they do not have their own names, are of the greatest importance for the study of black holes, since they confirmed their existence experimentally, and also gave important results for the study of gravity. We are talking about the event GW150914, which is called the collision of two black holes into one. This event made it possible to register.

Detecting black holes

Before considering methods for detecting black holes, one should answer the question - why is a black hole black? - the answer to it does not require deep knowledge in astrophysics and cosmology. The fact is that a black hole absorbs all radiation incident on it and does not emit at all, if we do not take into account the hypothetical. If we consider this phenomenon in more detail, we can assume that processes that lead to the release of energy in the form of electromagnetic radiation do not take place inside black holes. Then, if the BH does radiate, then it is in the Hawking spectrum (which coincides with the spectrum of a heated, absolutely black body). However, as mentioned earlier, this radiation was not detected, which suggests a completely low temperature of black holes.

Another generally accepted theory says that electromagnetic radiation is not at all capable of leaving the event horizon. It is most likely that photons (light particles) are not attracted by massive objects, since, according to the theory, they themselves have no mass. However, the black hole still "attracts" the photons of light by distorting space-time. If we imagine a black hole in space as a kind of depression on the smooth surface of space-time, then there is a certain distance from the center of the black hole, approaching to which the light will no longer be able to move away. That is, roughly speaking, the light begins to “fall” into the “pit”, which does not even have a “bottom”.

In addition to this, if we take into account the effect of gravitational redshift, then it is possible that light in a black hole loses its frequency, shifting along the spectrum to the region of low-frequency long-wavelength radiation, until it loses energy at all.

So, a black hole is black and therefore difficult to detect in space.

Detection methods

Consider the methods astronomers use to detect a black hole:

In addition to the methods mentioned above, scientists often associate objects such as black holes and. Quasars are some kind of clusters of cosmic bodies and gas, which are one of the brightest astronomical objects in the Universe. Since they have a high intensity of luminescence at relatively small sizes, there is reason to believe that the center of these objects is a supermassive black hole, which attracts surrounding matter. Due to such a powerful gravitational attraction, the attracted matter is so hot that it radiates intensely. Finding such objects is usually compared to finding a black hole. Sometimes quasars can radiate in two directions jets of heated plasma - relativistic jets. The reasons for the appearance of such jets (jets) are not completely clear, however, they are probably caused by the interaction of the magnetic fields of the BH and the accretion disk, and are not emitted by the direct black hole.

Jet in the galaxy M87 striking from the center of the BH

Summing up the above, one can imagine, up close: it is a spherical black object, around which strongly heated matter revolves, forming a luminous accretion disk.

Merging and colliding black holes

One of the most interesting phenomena in astrophysics is the collision of black holes, which also makes it possible to detect such massive astronomical bodies. Such processes are of interest not only to astrophysicists, since phenomena poorly studied by physicists become their consequence. The most striking example is the previously mentioned event called GW150914, when two black holes approached so much that they merged into one as a result of mutual gravitational attraction. An important consequence of this collision was the emergence of gravitational waves.

According to the definition of gravitational waves, these are changes in the gravitational field that propagate in a wave-like manner from massive moving objects. When two such objects approach each other, they begin to revolve around a common center of gravity. As they approach each other, their rotation around their own axis increases. Such variable fluctuations of the gravitational field at some point can form one powerful gravitational wave, which can propagate in space for millions of light years. So at a distance of 1.3 billion light years, two black holes collided, forming a powerful gravitational wave, which reached the Earth on September 14, 2015 and was recorded by the LIGO and VIRGO detectors.

How do black holes die?

Obviously, for a black hole to cease to exist, it will need to lose all of its mass. However, according to its definition, nothing can leave the limits of a black hole if it has crossed its event horizon. It is known that the Soviet theoretical physicist Vladimir Gribov was the first to mention the possibility of a black hole emitting particles in his discussion with another Soviet scientist Yakov Zeldovich. He argued that from the point of view of quantum mechanics, a black hole is capable of emitting particles through the tunneling effect. Later, with the help of quantum mechanics, the English theoretical physicist Stephen Hawking built his own, somewhat different theory. You can read more about this phenomenon. In short, in a vacuum there are so-called virtual particles that are constantly born in pairs and annihilate with each other, while not interacting with the outside world. But if such pairs appear on the event horizon of a black hole, then strong gravity is hypothetically capable of separating them, with one particle falling inside the BH, and the other going away from the black hole. And since the particle escaping from the hole can be observed, and therefore has positive energies, the particle falling into the hole must have negative energies. Thus, the black hole will lose its energy and there will be an effect called the evaporation of the black hole.

According to the available models of a black hole, as mentioned earlier, as its mass decreases, its radiation becomes more intense. Then, at the final stage of the existence of a BH, when it may decrease to the size of a quantum black hole, it will release a huge amount of energy in the form of radiation, which may be equivalent to thousands or even millions of atomic bombs. This event is somewhat reminiscent of the explosion of a black hole, like the same bomb. According to calculations, as a result of the Big Bang, primordial black holes could have arisen, and those of them, whose mass is about 10 12 kg, should have evaporated and exploded around our time. Be that as it may, such explosions have never been noticed by astronomers.

Despite Hawking's proposed mechanism for destroying black holes, the properties of Hawking's radiation cause a paradox in the framework of quantum mechanics. If a black hole absorbs a body, and then loses the mass resulting from the absorption of this body, then regardless of the nature of the body, the black hole will not differ from what it was before the absorption of the body. In this case, information about the body is forever lost. From the point of view of theoretical calculations, the transformation of the initial pure state into the obtained mixed ("thermal") state does not correspond to the current theory of quantum mechanics. This paradox is sometimes called the disappearance of information in a black hole. A definitive solution to this paradox has not been found. Known options for solving the paradox:

• Inconsistency of Hawking's theory. This entails the impossibility of the destruction of the black hole and its constant growth.
• The presence of white holes. In this case, the absorbed information does not disappear, but is simply thrown out into another Universe.
• Inconsistency of the generally accepted theory of quantum mechanics.

Unsolved problems of black hole physics

Apparently, what was described earlier, although black holes have been studied for a relatively long time, they still have many features, the mechanisms of which are still unknown to scientists.

• In 1970, an English scientist formulated the so-called. "The principle of cosmic censorship" - "Nature abhors a naked singularity." This means that the singularity is formed only in places hidden from view, like the center of a black hole. However, this principle has not yet been proven. There are also theoretical calculations according to which a "naked" singularity can occur.
• Nor has the “no hair theorem” been proven, according to which black holes have only three parameters.
• A complete theory of the black hole magnetosphere has not been developed.
• The nature and physics of gravitational singularity have not been studied.
• It is not known for certain what happens at the final stage of the existence of a black hole, and what remains after its quantum decay.

Interesting facts about black holes

Summing up the above, there are several interesting and unusual features of the nature of black holes:

• BHs have only three parameters: mass, electric charge, and angular momentum. As a result of such a small number of characteristics of this body, the theorem that asserts this is called the "no-hair theorem". This also gave rise to the phrase "a black hole has no hair", which means that two black holes are absolutely identical, their three parameters mentioned are the same.
• The BH density can be less than the air density, and the temperature is close to absolute zero. From this, it can be assumed that the formation of a black hole occurs not due to the compression of matter, but as a result of the accumulation of a large amount of matter in a certain volume.
• Time for bodies absorbed by BH runs much slower than for an external observer. In addition, the absorbed bodies are significantly stretched inside the black hole, which was called by scientists - spaghettification.
• There may be about a million black holes in our galaxy.
• There is probably a supermassive black hole at the center of every galaxy.
• In the future, according to the theoretical model, the universe will reach the so-called era of black holes, when black holes will become the dominant bodies in the universe.



BLACK HOLE
a region in space resulting from the complete gravitational collapse of matter, in which the gravitational attraction is so great that neither matter, nor light, nor other information carriers can leave it. Therefore, the interior of the black hole is not causally related to the rest of the universe; the physical processes taking place inside the black hole cannot influence the processes outside it. The 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 Earth, our further presentation is based mainly on theoretical results. Black holes predicted by general relativity (the theory of gravity proposed by Einstein in 1915) and other more modern theories of gravitation 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 have not taken them seriously for 25 years. However, astronomical discoveries in the mid-1960s made black holes look like a possible physical reality. Their discovery and study can fundamentally change our understanding of space and time.
Formation of black holes. While thermonuclear reactions take place in the interior of the star, they maintain high temperature and pressure, preventing the star from contracting under the influence of its own gravity. Over time, however, 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 a star is more than three solar masses, 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 circumference 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 constant of gravity. A black hole with a mass of 3 solar 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 contracting faster and faster, but as its surface approaches the gravitational radius, the compression will begin to slow down until it stops completely. In this case, the light coming from the star will fade and turn red until it goes out completely. This is because in the struggle with the gigantic force of gravity, light loses energy and it takes more and more time for it to reach the observer. When the surface of the star reaches the gravitational radius, the light that leaves it will take an infinite time to reach the observer (and in this case the photons will completely lose their energy). Consequently, the astronomer will never wait for this moment, much less see what is happening to the star under the event horizon. But theoretically this process can be investigated. The calculation of the idealized spherical collapse shows that in a short time the star is compressed to a point where infinitely large values ​​of density and gravity are achieved. This point is called the "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 is applicable down to very small spatial scales, which we are not yet sure of. In the microcosm, quantum laws operate, and the quantum theory of gravity has not yet been created. It is clear that quantum effects cannot stop a star from collapsing 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, very large black holes can be found 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, had to evaporate, losing their mass in the form of radiation and particle flows. But "primordial black holes" with a mass of more than 1015 g could have survived to this day. All calculations of the collapse of stars are made under the assumption of a slight deviation from spherical symmetry and show that the 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 that we discussed above. Physical laws near a bare singularity can have 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 the clock of a distant observer), 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. In 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 proved within the framework of general relativity by W. Israel, B. Carter, S. Hawking, and D. Robinson. According to general 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 kind of physical clock and rulers. For example, a molecule with a certain vibration frequency can play the role of a clock, the number of which between two events can be called a "time interval". It is remarkable that gravity acts on 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 near it is so great that the rays of light can move around it in a circle. Far from the black hole, its gravitational field is exactly described by Newton's theory for a body of the same mass, but near the black hole, gravity becomes much stronger than Newton's theory predicts. Any body falling on a black hole, long before crossing the event horizon, will be torn apart by powerful tidal gravitational forces arising from the difference in attraction 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 by a simple Hawking principle: the area of ​​the event horizon of a black hole never decreases, if one does not take into account the quantum creation 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). Under the influence of this idea, Hawking showed in 1974 that black holes can emit matter and radiation, but this will be noticeable only if the mass of the black hole itself is relatively small. Such black holes could be born immediately after the Big Bang, from which the expansion of the Universe began. The masses of these primordial black holes should be no more than 1015 g (like a small asteroid), and a size of 10-15 m (like a proton or neutron). The powerful gravitational field near the black hole creates particle-antiparticle pairs; one of the particles of each pair is absorbed by the hole, and the second is emitted outside. A black hole with a mass of 1015 g should behave like a body with a temperature of 1011 K. The idea of ​​"evaporation" of black holes completely contradicts the classical idea of ​​them as bodies incapable of radiating.
Search for black holes. Calculations within the framework of Einstein's general theory of relativity indicate only the possibility of the existence of black holes, but by no means 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 won't be able to spot a small dark object against a backdrop of cosmic blackness. But there is hope to detect a black hole by its interaction with the surrounding astronomical bodies, by its characteristic influence on them. Supermassive black holes can be located in the centers of galaxies, continuously devouring stars there. Having concentrated around the black hole, the stars should form central brightness peaks in the galactic cores; their searches are now 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 this is a black hole. In this way, in 1996, J. Moran and 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 the search for a black hole in binary systems, where it, together with a normal star, can revolve around a common center of mass. From the periodic Doppler shift of the lines in the spectrum of the star, one can understand that it is paired with a certain body and even estimate the mass of the latter. If this mass exceeds 3 times the mass of the Sun, and it is not possible to notice the radiation of the body itself, then it is very possible that this is a black hole. In a compact binary system, a black hole can trap gas from the surface of a normal star. Orbiting the black hole, this gas forms a disk and, spiraling closer to the black hole, heats up strongly and becomes a source of powerful X-ray radiation. Rapid fluctuations of this radiation should indicate that the gas is rapidly moving in a small radius orbit around the tiny massive object. Since the 1970s, several X-ray sources have been discovered in binary systems with clear indications of the presence of black holes. The most promising is the X-ray binary V 404 Cygnus, the mass of the invisible component of which is estimated at no less than 6 solar masses. Other notable black hole candidates are found in the binary X-ray systems Cygnus X-1, LMCX-3, V 616 Unicorn, QZ Chanterelles, and the X-ray novae Ophiuchus 1977, Fly 1981, and Scorpio 1994. With the exception of LMCX-3, located in the Large Magellanic Cloud, they are all located in our Galaxy at distances of about 8000 sv. years from Earth.
see also
COSMOLOGY;
GRAVITY;
GRAVITY COLLAPSE;
RELATIVITY;
EXTRA ATMOSPHERIC ASTRONOMY.
LITERATURE
Cherepashchuk A.M. Black hole masses in binary systems. Advances in Physical Sciences, vol. 166, p. 809, 1996

Collier's Encyclopedia. - Open Society. 2000 .

Synonyms:

See what "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

Cosmich. an object resulting from the compression of the body of gravity. forces to sizes smaller than its gravitational radius rg = 2g / c2 (where M is the mass of the body, G is a gravitational constant, with the numerical value of the speed of light). The prediction of the existence in ... ... Physical encyclopedia

Noun., Number of synonyms: 2 stars (503) unknown (11) ASIS synonym dictionary. V.N. Trishin. 2013 ... Synonym dictionary

Mysterious and elusive black holes. The laws of physics confirm the possibility of their existence in the universe, but many questions still remain. Numerous observations show that holes exist in the universe and there are more than a million of these objects.

What are black holes?

Back in 1915, when solving Einstein's equations, such a phenomenon as "black holes" was predicted. However, the scientific community became interested in them only in 1967. They were then called "collapsed stars", "frozen stars".

Now a black hole is called a region of time and space, which have such gravity that even a ray of light cannot get out of it.

How do black holes form?

There are several theories of the appearance of black holes, which are divided into hypothetical and realistic. The simplest and most widespread realistic theory is the theory of gravitational callapse of large stars.

When a sufficiently massive star before "death" grows in size and becomes unstable, consuming the last fuel. At the same time, the mass of the star remains unchanged, but its size decreases as the so-called compaction occurs. In other words, during compaction, the heavy nucleus "falls" into itself. In parallel with this, the compaction leads to a sharp increase in temperature inside the star and the outer layers of the celestial body are torn off, from which new stars are formed. At the same time in the center of the star - the core falls into its own "center". As a result of the action of the forces of gravity, the center collapses into a point - that is, the forces of gravity are so strong that they absorb the compacted core. This is how a black hole is born, which begins to distort space and time, so that even light cannot escape from it.

There is a supermassive black hole at the centers of all galaxies. According to Einstein's theory of relativity:

"Any mass distorts space and time."

Now imagine how much a black hole distorts time and space, because its mass is huge and at the same time squeezed into an ultra-small volume. This ability creates the following oddity:

“Black holes have the ability to practically stop time and compress space. Because of this extreme distortion, the holes become invisible to us. "

If black holes are not visible, how do we know they exist?

Yes, even though the black hole is invisible, but it should be noticeable due to the matter that falls into it. And also the stellar gas, which is attracted by the black hole, when approaching the event horizon, the gas temperature begins to rise to superhigh values, which leads to a glow. This is why black holes glow. Thanks to this, albeit weak glow, astronomers and astrophysicists explain the presence in the center of the galaxy of an object with a small volume, but a huge mass. At the moment, as a result of observations, about 1000 objects have been discovered that are similar in behavior to black holes.

Black holes and galaxies

How can black holes affect galaxies? This question plagues scientists around the world. There is a hypothesis according to which it is the black holes in the center of the galaxy that affect its shape and evolution. And that when two galaxies collide, black holes merge and during this process such a huge amount of energy and matter is ejected that new stars are formed.

Types of black holes

• According to the existing theory, there are three types of black holes: stellar, supermassive, miniature. And each of them was formed in a special way.
• - Black holes of stellar masses, it grows to a huge size and collapses.
  - Supermassive black holes, which can have a mass equivalent to millions of Suns, most likely exist in the centers of almost all galaxies, including our Milky Way. Scientists still have different hypotheses for the formation of supermassive black holes. So far, only one thing is known - supermassive black holes are a by-product of the formation of galaxies. Supermassive black holes - they differ from ordinary black holes in that they have a very large size, but paradoxically low density.
• - No one has yet been able to detect a miniature black hole that would have a mass less than the Sun. It is possible that miniature holes could have formed soon after the "Big Bang", which is the initial exact existence of our universe (about 13.7 billion years ago).
• - More recently, a new concept has been introduced as "white black holes". This is still a hypothetical black hole, which is the opposite of a black hole. Stephen Hawking actively studied the possibility of the existence of white holes.
• - Quantum black holes - they exist so far only in theory. Quantum black holes can form when ultra-small particles collide in a nuclear reaction.
• - Primordial black holes are also a theory. They were formed immediately after emergence.

At the moment, there are a large number of open questions that future generations have yet to answer. For example, can there really be so-called "wormholes" with which you can travel through space and time. What exactly happens inside a black hole and what laws do these phenomena obey. And what about the disappearance of information in a black hole?