In order for a black hole to form, it is necessary to compress the body to a certain critical density so that the radius of the compressed body is equal to its gravitational radius. The value of this critical density is inversely proportional to the square of the black hole's mass.
For a typical stellar mass black hole ( M=10M sun) the gravitational radius is 30 km, and the critical density is 2·10 14 g/cm 3 , that is, two hundred million tons per cubic centimeter. This density is very high compared to the average density of the Earth (5.5 g/cm3), it is equal to the density of the substance of the atomic nucleus.
For a black hole at the core of a galaxy ( M=10 10 M sun) the gravitational radius is 3 10 15 cm = 200 AU, which is five times the distance from the Sun to Pluto (1 astronomical unit - the average distance from the Earth to the Sun - is equal to 150 million km or 1.5 10 13 cm). The critical density in this case is equal to 0.2·10 -3 g/cm 3 , which is several times less than the density of air, equal to 1.3·10 -3 g/cm 3 (!).
For Earth ( M=3 10 –6 M sun) the gravitational radius is close to 9 mm, and the corresponding critical density is monstrously high: ρ cr = 2·10 27 g/cm 3 , which is 13 orders of magnitude higher than the density of the atomic nucleus.
If we take some imaginary spherical press and compress the Earth, keeping its mass, then when we reduce the radius of the Earth (6370 km) by four times, its second escape velocity will double and become equal to 22.4 km/s. If we compress the Earth so that its radius becomes approximately 9 mm, then the second cosmic velocity will take on a value equal to the speed of light c= 300000 km/s.
Further, the press will not be needed - the Earth compressed to such dimensions will already shrink itself. In the end, a black hole will form in place of the Earth, the radius of the event horizon of which will be close to 9 mm (if we neglect the rotation of the resulting black hole). In real conditions, of course, there is no super-powerful press - gravity "works". That is why black holes can only form when the interiors of very massive stars collapse, in which gravity is strong enough to compress matter to a critical density.
Star evolution
Black holes are formed in the final stages of the evolution of massive stars. Thermonuclear reactions take place in the depths of ordinary stars, huge energy is released and maintained heat(tens and hundreds of millions of degrees). The gravitational forces tend to compress the star, and the pressure forces of hot gas and radiation oppose this compression. Therefore, the star is in hydrostatic equilibrium.
In addition, a star can be in thermal equilibrium when the energy release due to thermonuclear reactions in its center is exactly equal to the power emitted by the star from the surface. As the star contracts and expands, the thermal equilibrium is disturbed. If the star is stationary, then its equilibrium is established in such a way that the negative potential energy of the star (the energy of gravitational contraction) is always twice the thermal energy in absolute value. Because of this, the star has an amazing property - negative heat capacity. Ordinary bodies have a positive heat capacity: a heated piece of iron, cooling down, that is, losing energy, lowers its temperature. In a star, the opposite is true: the more energy it loses in the form of radiation, the higher the temperature in its center becomes.
This strange, at first glance, feature finds a simple explanation: the star, radiating, slowly shrinks. When compressed, the potential energy is converted into the kinetic energy of falling layers of the star, and its interior is heated. And thermal energy, acquired by a star as a result of compression, is twice the energy that is lost in the form of radiation. As a result, the temperature of the interior of the star rises, and continuous thermonuclear fusion is carried out. chemical elements. For example, the reaction of converting hydrogen into helium in the current Sun takes place at a temperature of 15 million degrees. When, after 4 billion years, all hydrogen in the center of the Sun turns into helium, further synthesis of carbon atoms from helium atoms will require a much higher temperature, about 100 million degrees (the electric charge of helium nuclei is twice that of hydrogen nuclei, and in order to bring the nuclei closer together helium over a distance of 10–13 cm requires a much higher temperature). It is this temperature that will be provided due to the negative heat capacity of the Sun by the time of ignition in its depths of the thermonuclear reaction of converting helium into carbon.
white dwarfs
If the mass of the star is small, so that the mass of its core, affected by thermonuclear transformations, is less than 1.4 M sun , thermonuclear fusion of chemical elements may stop due to the so-called degeneracy of the electron gas in the star's core. In particular, the pressure of a degenerate gas depends on density, but does not depend on temperature, since the energy of quantum motions of electrons is much greater than the energy of their thermal motion.
The high pressure of the degenerate electron gas effectively counteracts the forces of gravitational contraction. Since pressure does not depend on temperature, the loss of energy by a star in the form of radiation does not lead to compression of its core. Therefore, gravitational energy is not released as additional heat. Therefore, the temperature in the evolving degenerate nucleus does not increase, which leads to the interruption of the chain of thermonuclear reactions.
The outer hydrogen shell, not affected by thermonuclear reactions, separates from the core of the star and forms a planetary nebula, glowing in the emission lines of hydrogen, helium and other elements. The central compact and relatively hot core of an evolved star of small mass is a white dwarf - an object with a radius of the order of the Earth's radius (~ 10 4 km), with a mass of less than 1.4 M sun and an average density of the order of a ton per cubic centimeter. White dwarfs are seen in in large numbers. Them total number in the Galaxy reaches 10 10 , that is, about 10% of the total mass of the observed matter in the Galaxy.
Thermonuclear combustion in a degenerate white dwarf can be unstable and lead to nuclear explosion a sufficiently massive white dwarf with a mass close to the so-called Chandrasekhar limit (1.4 M sun). Such explosions look like Type I supernova explosions, which have no hydrogen lines in the spectrum, but only lines of helium, carbon, oxygen and other heavy elements.
neutron stars
If the core of a star is degenerate, then as its mass approaches the limit of 1.4 M sun the usual degeneracy of the electron gas in the nucleus is replaced by the so-called relativistic degeneracy.
The quantum motions of degenerate electrons become so fast that their speeds approach the speed of light. In this case, the elasticity of the gas decreases, its ability to resist the forces of gravity decreases, and the star experiences a gravitational collapse. During the collapse, electrons are captured by protons, and matter is neutronized. This leads to the formation of a massive degenerate nucleus neutron star.
If the initial mass of the star's core exceeds 1.4 M sun , then a high temperature is reached in the nucleus, and electron degeneracy does not occur throughout its evolution. In this case, negative heat capacity works: as the star loses energy in the form of radiation, the temperature in its interior rises, and there is a continuous chain of thermonuclear reactions that convert hydrogen into helium, helium into carbon, carbon into oxygen, and so on, up to the elements of the iron group. The reaction of thermonuclear fusion of the nuclei of elements heavier than iron, is no longer with the release, but with the absorption of energy. Therefore, if the mass of the core of a star, consisting mainly of elements of the iron group, exceeds the Chandrasekhar limit of 1.4 M sun , but less than the so-called Oppenheimer–Volkov limit ~3 M sun , then at the end of the nuclear evolution of the star, a gravitational collapse of the core occurs, as a result of which the outer hydrogen shell of the star is thrown off, which is observed as a type II supernova explosion, in the spectrum of which powerful hydrogen lines are observed.
The collapse of the iron core leads to the formation of a neutron star.
When the massive core of a star that has reached a late stage of evolution is compressed, the temperature rises to gigantic values of the order of a billion degrees, when the nuclei of atoms begin to fall apart into neutrons and protons. Protons absorb electrons, turn into neutrons, and emit neutrinos. Neutrons, according to the Pauli quantum mechanical principle, under strong compression begin to effectively repel each other.
When the mass of the collapsing nucleus is less than 3 M sun , neutron velocities are much less than the speed of light, and the elasticity of matter, due to the effective repulsion of neutrons, can balance the forces of gravity and lead to the formation of a stable neutron star.
For the first time, the possibility of the existence of neutron stars was predicted in 1932 by the outstanding Soviet physicist Landau immediately after the discovery of the neutron in laboratory experiments. The radius of a neutron star is close to 10 km, its average density is hundreds of millions of tons per cubic centimeter.
When the mass of the collapsing stellar core is greater than 3 M sun , then, according to existing ideas, the resulting neutron star, cooling down, collapses into a black hole. The collapse of a neutron star into a black hole is also facilitated by the reverse fall of a part of the star's envelope thrown off during a supernova explosion.
A neutron star tends to rotate rapidly, because the normal star that gave birth to it can have significant angular momentum. When the core of a star collapses into a neutron star, the characteristic dimensions of the star decrease from R= 10 5 –10 6 km to R≈ 10 km. As the size of a star decreases, its moment of inertia decreases. To maintain the angular momentum, the speed of axial rotation must increase sharply. For example, if the Sun, which rotates with a period of about a month, is compressed to the size of a neutron star, then the rotation period will decrease to 10 -3 seconds.
Single neutron stars with a strong magnetic field manifest themselves as radio pulsars - sources of strictly periodic radio emission pulses that arise when the energy of the rapid rotation of a neutron star is converted into directed radio emission. In binary systems, accreting neutron stars exhibit the phenomenon of an X-ray pulsar and a Type 1 X-ray burster.
Strictly periodic radiation pulsations cannot be expected from a black hole, since a black hole has no observable surface and no magnetic field. As physicists often express, black holes do not have "hair" - all fields and all inhomogeneities near the event horizon are radiated during the formation of a black hole from collapsing matter in the form of a stream of gravitational waves. As a result, the formed black hole has only three characteristics: mass, angular momentum and electric charge. All the individual properties of the collapsing matter during the formation of a black hole are forgotten: for example, black holes formed from iron and from water have the same characteristics, other things being equal.
As General Relativity (GR) predicts, stars whose iron core masses at the end of their evolution exceed 3 M sun, experience unlimited compression (relativistic collapse) with the formation of a black hole. This is explained by the fact that in general relativity the gravitational forces tending to compress a star are determined by the energy density, and at the enormous matter densities achieved by compressing such a massive star core, the main contribution to the energy density is made not by the rest energy of particles, but by the energy of their motion and interaction . It turns out that in general relativity the pressure of matter at very high densities seems to "weigh" itself: the greater the pressure, the greater the energy density and, consequently, the greater the gravitational forces tending to compress the matter. In addition, under strong gravitational fields, the effects of space-time curvature become fundamentally important, which also contributes to the unlimited compression of the star's core and its transformation into a black hole (Fig. 3).
In conclusion, we note that black holes that formed in our era (for example, the black hole in the Cygnus X-1 system), strictly speaking, are not one hundred percent black holes, because due to the relativistic slowing down of time for a distant observer, their event horizons are still have not formed. The surfaces of such collapsing stars look to the earthly observer as frozen, approaching their event horizons for an infinitely long time.
In order for black holes from such collapsing objects to form completely, we must wait for everything indefinitely big time the existence of our universe. It should be emphasized, however, that already in the first seconds of the relativistic collapse, the surface of the collapsing star for an observer from Earth approaches very close to the event horizon, and all processes on this surface slow down infinitely.
A black hole is one of the most mysterious objects in the universe. Many famous scientists, including Albert Einstein, spoke about the possibility of the existence of black holes. Black holes owe their name to American astrophysicist John Wheeler. There are two types of black holes in the universe. The first is massive black holes - huge bodies, the mass of which is millions of times greater than the mass of the Sun. Such objects, as scientists suggest, are located in the center of galaxies. There is also a giant black hole at the center of our Galaxy. Scientists have not yet been able to find out the reasons for the appearance of such huge cosmic bodies.
Point of view
Modern science underestimates the importance of the concept of "energy of time", introduced into scientific use by the Soviet astrophysicist N.A. Kozyrev.
We have finalized the idea of the energy of time, as a result of which a new philosophical theory has appeared - "ideal materialism". This theory provides an alternative explanation for the nature and structure of black holes. Black holes in the theory of ideal materialism play a key role, and, in particular, in the processes of origin and balance of time energy. The theory explains why supermassive black holes are located at the centers of almost all galaxies. On the site it will be possible to get acquainted with this theory, but after appropriate preparation. see site materials).
The area in space and time, the attraction of gravity of which is so strong that even objects moving at the speed of light cannot leave it, is called black hole. The boundary of a black hole is referred to as the concept of "event horizon", and its size - as the radius of gravity. In the simplest case, it is equal to the Schwarzschild radius.
The fact that the existence of black holes is theoretically possible can be proven from some of Einstein's exact equations. The first of them was obtained in 1915 by the same Karl Schwarzschild. It is not known who was the first to invent the term. One can only say that the very designation of the phenomenon was popularized thanks to John Archibald Wheeler, who first published the lecture “Our Universe: the Known and Unknown (Our Universe: the Known and Unknown)”, where it was used. Much earlier, these objects were called "collapsed stars" or "collapsers".
The question of whether black holes actually exist is related to the real existence of gravity. AT modern science The most realistic theory of gravity is the general theory of relativity, which clearly defines the possibility of the existence of black holes. But, nevertheless, their existence is also possible within the framework of other theories, so the data is constantly analyzed and interpreted.
The statement about the existence of really existing black holes should be understood as confirmation of the existence of dense and massive astronomical objects, which can be interpreted as black holes of the theory of relativity. In addition to this, to similar phenomenon stars can be attributed to the late stages of the collapse. Modern astrophysicists do not attach importance to the difference between such stars and real black holes.
Many of those who have studied or are still studying astronomy know that what is a black hole and where does she come from. But still, for ordinary people For those who are not particularly interested in this, I will briefly explain everything.
Black hole- this is a certain area in the space of space or even time in it. Only this is not an ordinary area. It has a very strong gravity (attraction). Moreover, it is so strong that something cannot get out of a black hole if it gets there! Even the sun's rays cannot avoid falling into a black hole if it passes nearby. Although, be aware that the sun's rays (light) move at the speed of light - 300,000 km/sec.
Previously, black holes were called differently: collapsars, collapsed stars, frozen stars, and so on. Why? Because black holes are created by dead stars.
The fact is that when a star depletes all its energy, it becomes a very hot giant, and as a result, it explodes. Its core, with some probability, can shrink very strongly. And with incredible speed. In some cases, after the explosion of a star, a black, invisible hole is formed, which devours everything in its path. All objects that even move at the speed of light.
A black hole doesn't care what objects it absorbs. It could be like spaceships and the rays of the sun. It doesn't matter how fast the object is moving. The black hole also does not care what the mass of the object is. It can devour everything from cosmic microbes or dust all the way to the stars themselves.
Unfortunately, no one has yet figured out what is happening inside a black hole. Some suggest that an object that falls into a black hole breaks with incredible force. Others believe that the exit from the black hole can lead to another, some kind of second universe. Still others believe that (most likely) if you go from the entrance to the exit of a black hole, it can simply throw you into another part of the universe.
Black hole in space
Black hole- This space object incredible density, possessing absolute gravity, such that any cosmic body and even space and time itself are absorbed by it.
Black holes govern itself the evolution of the universe. they are in a central place, but you cannot see them, you can find their signs. Although black holes have the ability to destroy, they also help build galaxies.
Some scientists believe that black holes are the gateway to parallel universes. which may well be. There is an opinion that black holes have the opposite, the so-called white holes . having anti-gravity properties.
Black hole is born inside the largest stars, when they die, the force of gravity destroys them, thereby leading to powerful explosion supernova.
The existence of black holes was predicted by Karl Schwarzschild
Karl Schwarzschild was the first to apply Einstein's general theory of relativity to justify the existence of a "point of no return". Einstein himself did not think about black holes, although his theory makes it possible to predict their existence.
Schwarzschild made his suggestion in 1915, just after Einstein published his general theory of relativity. That's when the term "Schwarzschild radius" came about, a value that tells you how much you have to compress an object to make it a black hole.
Theoretically, anything can become a black hole, given enough compression. The denser the object, the stronger the gravitational field it creates. For example, the Earth would become a black hole if an object the size of a peanut had its mass.
Sources: www.alienguest.ru, cosmos-online.ru, kak-prosto.net, nasha-vselennaya.ru, www.qwrt.ru
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Black holes - perhaps the most mysterious and enigmatic astronomical objects in our Universe, have attracted the attention of pundits and excite the imagination of science fiction writers since their discovery. What are black holes and what do they look like? Black holes are extinguished stars, due to their physical features, which have such high density and gravity so powerful that not even light can escape.
The 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 someone D. Michel (an English priest from Yorkshire, who is fond of astronomy at his leisure) back in 1783. According to his calculations, if we take ours and compress it (in modern computer terms, archive it) to a radius of 3 km, such a large (just huge) gravitational force is formed that even light cannot leave it. This is how the concept of “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 takes place.
Later, in 1918, the great scientist Albert Einstein wrote about the issue of black holes in the context of the theory of relativity. But only in 1967, through the efforts of the American astrophysicist John Wheeler, the concept of black holes finally won a place in academic circles.
Be that as it may, both D. Michel, and Albert Einstein, and John Wheeler in their works assumed only the theoretical existence of these mysterious celestial objects in outer space, however, the true discovery of black holes took place in 1971, it was then that they were first noticed in space. telescope.
This is what a black hole looks like.
How do black holes form in space?
As we know from astrophysics, all stars (including our Sun) have some limited amount 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 "extinction" 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, which have incredibly impressive dimensions, usually turn into a black hole - due to the compression of these most incredible sizes, a multiple increase in the mass and gravitational force of the newly formed black hole occurs, which turns into a kind of galactic vacuum cleaner - absorbs everything and everything around it.
A black hole swallows a star.
A small remark - our Sun, by galactic standards, is not at all big star and after extinction, which will occur in about a few billion years, most likely it will not turn into a black hole.
But let's be honest with you - today, scientists still do not know all the intricacies of the formation of a black hole, undoubtedly, this is an extremely complex astrophysical process, which itself can last millions of light years. Although it is possible to move in this direction, the detection and subsequent study of the so-called intermediate black holes, that is, stars that are in a state of extinction, in which an active process of black hole formation is taking place, could be made. By the way, a similar star was discovered by astronomers in 2014 in the arm of a spiral galaxy.
How many black holes exist in the universe
According to the theories of modern scientists in our galaxy milky way There may be up to hundreds of millions of black holes. There may be no less of them in the galaxy next to us, to which there is nothing to fly from our Milky Way - 2.5 million light years.
Theory of black holes
Despite the huge 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 a black hole only at the moment of its "meal" - the absorption of another star, at this moment a 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 flows many times slower than usual, and if you were there, then returning back (if you were so lucky, of course) you would be surprised to notice that centuries have passed on Earth, and you won’t even grow old have time. Although let's be truthful, if you were inside a black hole, you would hardly have survived, since the gravitational force there is such that any material object would simply be torn apart, not even into parts, into atoms.
But if you were even close to a black hole, within the limits of its gravitational field, then you would also have a hard time, because the more you resisted its gravity, trying to fly away, the faster you would fall into it. The reason for this seemingly paradox is the gravitational vortex field, which 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 give off evaporation. True, this applies only to holes of relatively small mass. The powerful gravity around them creates pairs of particles and antiparticles, one of the pair is pulled inward by the hole, and the second is ejected outward. Thus, a black hole radiates hard antiparticles and gamma rays. This evaporation or radiation from a black hole was named after the scientist who discovered it - "Hawking radiation".
The biggest black hole
According to the theory of black holes, in 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 have discovered the two largest black holes known to date, they are in two nearby galaxies: NGC 3842 and NGC 4849.
NGC 3842 is the brightest galaxy in the constellation Leo, located at a distance of 320 million light-years from us. In the center of it there is a huge black hole with a mass of 9.7 billion solar masses.
NGC 4849 is a galaxy in the Coma cluster, 335 million light-years away, boasting an equally impressive black hole.
The zones of action of the gravitational field of these giant black holes, or in academic terms, their event horizon, is about 5 times the distance from the Sun to! Such a black hole would eat our solar system and wouldn't even flinch.
The smallest black hole
But there are very small representatives in the vast family of black holes. So the most dwarf black hole discovered by scientists at the moment in its mass is only 3 times the mass of our Sun. In fact, this is the theoretical minimum necessary for the formation of a black hole, if that star were a little 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 have discovered that a black hole from one galaxy is being eaten by another large 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 themselves can generate new universes.
- Black holes can evaporate over time. We wrote above that it was discovered by the English scientist Stephen Hawking that black holes have the property of radiation and after some very long period of time, when there is nothing to absorb around, the black hole will begin to evaporate more, until eventually 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 in the conditions of a black hole will 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 you know, 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.
Both for scientists of the past centuries, and for researchers of our time, the greatest mystery of space is a black hole. What is inside this completely unfamiliar system for physics? What laws apply there? How does time pass in a black hole, and why can't even light quanta escape from it? Now we will try, of course, from the point of view of theory, and not practice, to understand what is inside a black hole, why it, in principle, was formed and exists, how it attracts the objects that surround it.
First, let's describe this object.
So, a certain region of space in the Universe is called a black hole. It is impossible to single it out as a separate star or planet, since it is neither a solid nor a gaseous body. Without a basic understanding of what spacetime is and how these dimensions can change, it is impossible to comprehend what is inside a black hole. The fact is that this area is not only a spatial unit. which distorts both the three dimensions known to us (length, width and height) and the timeline. Scientists are sure that in the region of the horizon (the so-called area surrounding the hole), time takes on a spatial meaning and can move both forward and backward.
Learn the secrets of gravity
If we want to understand what is inside a black hole, we will consider in detail what gravity is. It is this phenomenon that is key in understanding the nature of the so-called "wormholes", from which even light cannot escape. Gravity is the interaction between all bodies that have a material basis. The strength of such gravity depends on the molecular composition of bodies, on the concentration of atoms, and also on their composition. The more particles collapse in a certain area of space, the greater the gravitational force. This is inextricably linked to the Big Bang Theory, when our universe was the size of a pea. It was a state of maximum singularity, and as a result of a flash of light quanta, space began to expand due to the fact that the particles repelled each other. Exactly the opposite is described by scientists as a black hole. What's inside such a thing according to TBZ? Singularity, which is equal to the indicators inherent in our Universe at the time of its birth.
How does matter get into a wormhole?
There is an opinion that a person will never be able to understand what is happening inside a black hole. Since, once there, he will be literally crushed by gravity and gravity. Actually this is not true. Yes, indeed, a black hole is a region of singularity, where everything is compressed to the maximum. But this is not a “space vacuum cleaner” at all, which is capable of drawing all the planets and stars into itself. Any material object that is on the event horizon will observe a strong distortion of space and time (so far, these units stand apart). The Euclidean system of geometry will begin to falter, in other words, they will intersect, the outlines of stereometric figures will cease to be familiar. As for time, it will gradually slow down. The closer you get to the hole, the slower the clock will go relative to Earth time, but you won't notice it. When hitting the "wormhole", the body will fall at zero speed, but this unit will be equal to infinity. curvature, which equates the infinite to zero, which finally stops time in the region of the singularity.
Response to emitted light
The only object in space that attracts light is a black hole. What is inside it and in what form it is there is unknown, but they believe that this is pitch darkness, which is impossible to imagine. Light quanta, getting there, do not just disappear. Their mass is multiplied by the mass of the singularity, which makes it even larger and magnifies it. Thus, if you turn on a flashlight inside the wormhole to look around, it will not glow. The emitted quanta will constantly multiply by the mass of the hole, and, roughly speaking, you will only aggravate your situation.
Black holes everywhere
As we have already figured out, the basis of education is gravity, the value of which there is millions of times greater than on Earth. Accurate Representation about what a black hole is, was given to the world by Karl Schwarzschild, who, in fact, discovered the very event horizon and the point of no return, and also established that zero in a singularity state is equal to infinity. In his opinion, a black hole can form anywhere in space. In this case, a certain material object having a spherical shape must reach the gravitational radius. For example, the mass of our planet must fit in the volume of one pea to become a black hole. And the Sun should have a diameter of 5 kilometers with its mass - then its state will become singular.
New world formation horizon
The laws of physics and geometry work perfectly on earth and in open space, where space approaches vacuum. But they completely lose their significance on the event horizon. That is why, from a mathematical point of view, it is impossible to calculate what is inside a black hole. The pictures that you can come up with if you bend space in accordance with our ideas about the world are certainly far from the truth. It has only been established that time here turns into a spatial unit and, most likely, some more dimensions are added to the existing ones. This makes it possible to believe that completely different worlds are formed inside the black hole (the photo, as you know, will not show this, since the light eats itself there). These universes may be composed of antimatter, which is currently unfamiliar to scientists. There are also versions that the sphere of no return is just a portal that leads either to another world or to other points in our Universe.
Birth and death
Much more than the existence of a black hole, is its birth or disappearance. The sphere that distorts space-time, as we have already found out, is formed as a result of collapse. This may be the explosion of a large star, the collision of two or more bodies in space, and so on. But how did matter, which could theoretically be felt, become a realm of time distortion? The puzzle is in progress. But it is followed by a second question - why do such spheres of no return disappear? And if black holes evaporate, then why doesn't that light and all the cosmic matter that they pulled in come out of them? When the matter in the singularity zone begins to expand, gravity gradually decreases. As a result, the black hole simply dissolves, and ordinary vacuum outer space remains in its place. Another mystery follows from this - where did everything that got into it go?
Gravity - our key to a happy future?
Researchers are confident that the energy future of mankind can be formed by a black hole. What is inside this system is still unknown, but it was possible to establish that on the event horizon any matter is transformed into energy, but, of course, partially. For example, a person, finding himself near the point of no return, will give 10 percent of his matter for its processing into energy. This figure is simply colossal, it has become a sensation among astronomers. The fact is that on Earth, when matter is processed into energy by only 0.7 percent.
S. TRANKOVSKY
Among the most important and interesting problems of modern physics and astrophysics, Academician V. L. Ginzburg named questions related to black holes (see Science and Life, Nos. 11, 12, 1999). The existence of these strange objects was predicted more than two hundred years ago, the conditions leading to their formation were precisely calculated in the late 30s of the XX century, and astrophysics came to grips with them less than forty years ago. Today scientific journals around the world publish thousands of articles on black holes every year.
The formation of a black hole can occur in three ways.
This is how it is customary to depict the processes taking place in the vicinity of a collapsing black hole. As time passes (Y), the space (X) around it (shaded area) shrinks towards the singularity.
The gravitational field of a black hole introduces strong distortions into the geometry of space.
A black hole, invisible through a telescope, reveals itself only by its gravitational influence.
In the powerful gravitational field of a black hole, particle-antiparticle pairs are born.
The birth of a particle-antiparticle pair in the laboratory.
HOW THEY APPEAR
A luminous celestial body with a density equal to that of the Earth and a diameter two hundred and fifty times greater than the diameter of the Sun, due to the force of its attraction, will not allow its light to reach us. Thus, it is possible that the largest luminous bodies in the universe, precisely because of their size, remain invisible.
Pierre Simon Laplace.
Presentation of the system of the world. 1796
In 1783, the English mathematician John Mitchell, and thirteen years later independently of him, the French astronomer and mathematician Pierre Simon Laplace conducted a very strange study. They considered the conditions under which light would not be able to leave a star.
The scientists' logic was simple. For any astronomical object (planet or star), you can calculate the so-called escape velocity, or the second cosmic speed, which allows any body or particle to leave it forever. And in the physics of that time, the Newtonian theory reigned supreme, according to which light is a stream of particles (before the theory electromagnetic waves and there were still almost a hundred and fifty years left). The escape velocity of particles can be calculated based on the equality potential energy on the surface of the planet and the kinetic energy of the body, "escaped" to an infinitely long distance. This speed is determined by the formula #1#
where M is the mass of the space object, R is its radius, G is the gravitational constant.
From here, the radius of a body of a given mass is easily obtained (later called the "gravitational radius r g "), at which the escape velocity is equal to the speed of light:
This means that a star compressed into a sphere with radius r g< 2GM/c 2 will stop emitting - the light will not be able to leave it. A black hole will appear in the universe.
It is easy to calculate that the Sun (its mass is 2.1033 g) will turn into a black hole if it shrinks to a radius of about 3 kilometers. The density of its substance in this case will reach 10 16 g/cm 3 . The radius of the Earth, compressed to the state of a black hole, would decrease to about one centimeter.
It seemed incredible that forces could be found in nature that could compress a star to such an insignificant size. Therefore, the conclusions from the work of Mitchell and Laplace for more than a hundred years were considered something like a mathematical paradox that has no physical meaning.
A rigorous mathematical proof that such an exotic object in space is possible was obtained only in 1916. German astronomer Karl Schwarzschild, after analyzing the equations general theory relativity of Albert Einstein, got an interesting result. Having studied the motion of a particle in the gravitational field of a massive body, he came to the conclusion that the equation loses its physical meaning (its solution goes to infinity) when r= 0 and r = r g.
The points at which the characteristics of the field lose their meaning are called singular, that is, special. The singularity at the zero point reflects a point, or, what is the same, a centrally symmetric field structure (after all, any spherical body - a star or a planet - can be represented as a material point). And the points located on a spherical surface with a radius r g , form the very surface from which the escape velocity is equal to the speed of light. In the general theory of relativity, it is called the Schwarzschild singular sphere or the event horizon (why - it will become clear later).
Already on the example of objects familiar to us - the Earth and the Sun - it is clear that black holes are very strange objects. Even astronomers dealing with matter at extreme temperatures, density and pressure consider them to be very exotic, and until recently not everyone believed in their existence. However, the first indications of the possibility of the formation of black holes were already contained in A. Einstein's general theory of relativity, created in 1915. The English astronomer Arthur Eddington, one of the first interpreters and popularizers of the theory of relativity, in the 1930s derived a system of equations describing internal structure stars. It follows from them that the star is in equilibrium under the action of oppositely directed gravitational forces and internal pressure created by the motion of hot plasma particles inside the luminary and by the pressure of radiation generated in its depths. And this means that the star is a gas ball, in the center of which there is a high temperature, gradually decreasing towards the periphery. From the equations, in particular, it followed that the surface temperature of the Sun is about 5500 degrees (which is quite consistent with the data of astronomical measurements), and in its center there should be about 10 million degrees. This allowed Eddington to make a prophetic conclusion: at such a temperature, a thermonuclear reaction is “ignited”, sufficient to ensure the glow of the Sun. Atomic physicists of that time did not agree with this. It seemed to them that it was too "cold" in the bowels of the star: the temperature there was insufficient for the reaction to "go". To this the enraged theorist replied: "Look for a hotter place!"
And in the end, he turned out to be right: a thermonuclear reaction really takes place in the center of the star (another thing is that the so-called "standard solar model", based on ideas about thermonuclear fusion, apparently turned out to be incorrect - see, for example, "Science and life" No. 2, 3, 2000). Nevertheless, the reaction in the center of the star takes place, the star shines, and the radiation that occurs in this case keeps it in a stable state. But now the nuclear "fuel" in the star burns out. The release of energy stops, the radiation goes out, and the force holding back the gravitational attraction disappears. There is a limit on the mass of a star, after which the star begins to irreversibly shrink. Calculations show that this happens if the mass of the star exceeds two or three solar masses.
GRAVITATIONAL COLLAPSE
At first, the rate of contraction of the star is small, but its rate continuously increases, since the force of attraction is inversely proportional to the square of the distance. Compression becomes irreversible, there are no forces capable of counteracting self-gravity. This process is called gravitational collapse. The speed of the shell of the star towards its center increases, approaching the speed of light. And here the effects of the theory of relativity begin to play a role.
The escape velocity was calculated based on Newtonian ideas about the nature of light. From the point of view of general relativity, phenomena in the vicinity of a collapsing star occur somewhat differently. In its powerful gravitational field, the so-called gravitational redshift occurs. This means that the frequency of radiation coming from a massive object is shifted towards low frequencies. In the limit, at the boundary of the Schwarzschild sphere, the radiation frequency becomes equal to zero. That is, an observer who is outside of it will not be able to find out anything about what is happening inside. That is why the Schwarzschild sphere is called the event horizon.
But reducing the frequency is tantamount to slowing down time, and when the frequency becomes zero, time stops. This means that an outside observer will see a very strange picture: the shell of a star falling with increasing acceleration, instead of reaching the speed of light, stops. From his point of view, the contraction will stop as soon as the size of the star approaches the gravitational radius
mustache. He will never see even one particle "diving" under the Schwarzschild sphere. But for a hypothetical observer falling into a black hole, everything will end in a matter of moments according to his watch. Thus, the gravitational collapse time of a star the size of the Sun will be 29 minutes, and a much denser and more compact neutron star - only 1/20,000 of a second. And here he is in trouble, connected with the geometry of space-time near a black hole.
The observer enters a curved space. Near the gravitational radius, the gravitational forces become infinitely large; they stretch the rocket with the astronaut-observer into an infinitely thin thread of infinite length. But he himself will not notice this: all his deformations will correspond to the distortions of space-time coordinates. These considerations, of course, refer to the ideal, hypothetical case. Any real body will be torn apart by tidal forces long before approaching the Schwarzschild sphere.
BLACK HOLES DIMENSIONS
The size of a black hole, or rather, the radius of the Schwarzschild sphere is proportional to the mass of the star. And since astrophysics does not impose any restrictions on the size of a star, a black hole can be arbitrarily large. If, for example, it arose during the collapse of a star with a mass of 10 8 solar masses (or due to the merger of hundreds of thousands, or even millions of relatively small stars), its radius would be about 300 million kilometers, twice the Earth's orbit. And the average density of the substance of such a giant is close to the density of water.
Apparently, it is precisely such black holes that are found in the centers of galaxies. In any case, astronomers today count about fifty galaxies, in the center of which, judging by indirect signs (we will talk about them below), there are black holes with a mass of about a billion (10 9) solar ones. Apparently, our Galaxy also has its own black hole; its mass was estimated quite accurately - 2.4. 10 6 ±10% of the mass of the Sun.
The theory assumes that, along with such supergiants, black mini-holes with a mass of about 10 14 g and a radius of about 10 -12 cm (the size of the atomic nucleus) should have arisen. They could appear in the first moments of the existence of the Universe as a manifestation of a very strong inhomogeneity of space-time with a colossal energy density. The conditions that existed then in the Universe are now realized by researchers at powerful colliders (accelerators on colliding beams). Experiments at CERN earlier this year made it possible to obtain quark-gluon plasma - matter that existed before the appearance of elementary particles. Research into this state of matter continues at Brookhaven, the American accelerator center. It is capable of accelerating particles to energies one and a half to two orders of magnitude higher than an accelerator in
CERN. The upcoming experiment caused serious anxiety: will a black mini-hole arise during its implementation, which will bend our space and destroy the Earth?
This fear caused such a strong response that the US government was forced to convene an authoritative commission to test this possibility. The commission, which consisted of prominent researchers, concluded that the energy of the accelerator is too low for a black hole to form (this experiment is described in the journal Nauka i Zhizn, No. 3, 2000).
HOW TO SEE THE INVISIBLE
Black holes emit nothing, not even light. However, astronomers have learned to see them, or rather, to find "candidates" for this role. There are three ways to detect a black hole.
1. It is necessary to follow the circulation of stars in clusters around a certain center of gravity. If it turns out that there is nothing in this center, and the stars revolve, as it were, around an empty place, we can say quite confidently: there is a black hole in this "emptiness". It was on this basis that the presence of a black hole in the center of our Galaxy was assumed and its mass was estimated.
2. A black hole actively sucks matter into itself from the surrounding space. Interstellar dust, gas, matter of nearby stars fall on it in a spiral, forming the so-called accretion disk, similar to the ring of Saturn. (This is exactly what was frightening in the Brookhaven experiment: a black mini-hole that arose in the accelerator will begin to suck the Earth into itself, and this process could not be stopped by any forces.) Approaching the Schwarzschild sphere, particles experience acceleration and begin to radiate in the X-ray range. This radiation has a characteristic spectrum similar to the well-studied radiation of particles accelerated in a synchrotron. And if such radiation comes from some region of the Universe, it is safe to say that there must be a black hole there.
3. When two black holes merge, gravitational radiation occurs. It is calculated that if the mass of each is about ten solar masses, then when they merge in a matter of hours, energy equivalent to 1% of their total mass will be released in the form of gravitational waves. This is a thousand times more than the light, heat and other energy that the Sun has emitted over the entire period of its existence - five billion years. They hope to detect gravitational radiation with the help of gravitational-wave observatories LIGO and others, which are now being built in America and Europe with the participation of Russian researchers (see "Science and Life" No. 5, 2000).
And yet, although astronomers have no doubts about the existence of black holes, no one can categorically state that exactly one of them is located at a given point in space. Scientific ethics, the conscientiousness of the researcher require an unambiguous answer to the question posed, which does not tolerate discrepancies. It is not enough to estimate the mass of an invisible object, you need to measure its radius and show that it does not exceed the Schwarzschild radius. And even within our Galaxy, this problem is not yet solved. That is why scientists show a certain restraint in reporting their discovery, and scientific journals are literally full of reports of theoretical work and observations of effects that can shed light on their mystery.
True, black holes also have one more property, predicted theoretically, which, perhaps, would make it possible to see them. But, however, under one condition: the mass of the black hole must be much less than the mass of the Sun.
A BLACK HOLE MAY BE "WHITE"
For a long time, black holes were considered the embodiment of darkness, objects that in a vacuum, in the absence of absorption of matter, do not radiate anything. However, in 1974, the famous English theorist Stephen Hawking showed that black holes can be assigned a temperature and therefore must radiate.
According to the concepts of quantum mechanics, vacuum is not a void, but a kind of "foam of space-time", a hodgepodge of virtual (unobservable in our world) particles. However, quantum energy fluctuations are capable of "thrown" a particle-antiparticle pair out of vacuum. For example, when two or three gamma quanta collide, an electron and a positron will appear as if from nothing. This and similar phenomena have been repeatedly observed in laboratories.
It is quantum fluctuations that determine the processes of radiation from black holes. If a pair of particles with energies E and -E(the total energy of the pair is zero), arises in the vicinity of the Schwarzschild sphere, the further fate of the particles will be different. They can annihilate almost immediately or go under the event horizon together. In this case, the state of the black hole will not change. But if only one particle goes under the horizon, the observer will register another, and it will seem to him that it was generated by a black hole. In this case, a black hole that has absorbed a particle with energy -E, will reduce its energy, and with energy E- increase.
Hawking calculated the rates at which all these processes go, and came to the conclusion that the probability of absorption of particles with negative energy is higher. This means that the black hole loses energy and mass - it evaporates. In addition, it radiates as a completely black body with a temperature T = 6 . 10 -8 M with / M kelvins, where M c is the mass of the Sun (2.1033 g), M is the mass of the black hole. This simple relationship shows that the temperature of a black hole with a mass six times the Sun's is one hundred millionth of a degree. It is clear that such a cold body radiates practically nothing, and all the above reasoning remains valid. Another thing - mini-holes. It is easy to see that with a mass of 10 14 -10 30 grams, they are heated to tens of thousands of degrees and are white hot! However, it should be immediately noted that there are no contradictions with the properties of black holes: this radiation is emitted by a layer above the Schwarzschild sphere, and not below it.
So, the black hole, which seemed to be forever frozen object, sooner or later disappears, evaporating. Moreover, as it "loses weight", the rate of evaporation increases, but it still takes an extremely long time. It is estimated that mini-holes weighing 10 14 grams, which appeared immediately after the Big Bang 10-15 billion years ago, should evaporate completely by our time. At the last stage of their life, their temperature reaches a colossal value, so the products of evaporation must be particles of extremely high energy. It is possible that they are the ones that generate wide atmospheric showers - EASs in the Earth's atmosphere. In any case, the origin of anomalously high-energy particles is another important and interesting problem that can be closely related to the no less exciting questions of black hole physics.
