Of all the objects known to mankind that are located in outer space, black holes produce the most eerie and incomprehensible impression. This feeling covers almost every person when black holes are mentioned, despite the fact that humanity has known about them for more than a century and a half. The first knowledge about these phenomena was obtained long before Einstein’s publications on the theory of relativity. But real confirmation of the existence of these objects was received not so long ago.
Of course, black holes are rightfully famous for their strange physical characteristics, which give rise to even more mysteries in the Universe. They easily challenge all cosmic laws of physics and cosmic mechanics. In order to understand all the details and principles of the existence of such a phenomenon as a cosmic hole, we need to familiarize ourselves with modern achievements in astronomy and use our imagination; in addition, we will have to go beyond standard concepts. To make it easier to understand and get acquainted with cosmic holes, the portal site has prepared a lot of interesting information regarding these phenomena in the Universe.
Features of black holes from the portal site
First of all, it should be noted that black holes do not come out of nowhere, they are formed from stars that are gigantic in size and mass. Moreover, the biggest feature and uniqueness of every black hole is that they have a very strong gravitational pull. The force of attraction of objects to a black hole exceeds the second escape velocity. Such gravity indicators indicate that even light rays cannot escape from the field of action of a black hole, since they have a much lower speed.
The peculiarity of attraction is that it attracts all objects that are in close proximity. The larger the object that passes in the vicinity of the black hole, the more influence and attraction it will receive. Accordingly, we can conclude that the larger the object, the stronger it is attracted by the black hole, and in order to avoid such influence, the cosmic body must have very high speeds of movement.
It is also safe to note that in the entire Universe there is no body that could avoid the attraction of a black hole if it finds itself in close proximity, since even the fastest light stream cannot escape this influence. The theory of relativity, developed by Einstein, is excellent for understanding the characteristics of black holes. According to this theory, gravity can influence time and distort space. It also states that the larger an object located in outer space, the more it slows down time. In the vicinity of the black hole itself, time seems to stop completely. If a spacecraft were to enter the field of action of a space hole, one would observe how it would slow down as it approached, and ultimately disappear altogether.
You shouldn’t be too scared of phenomena such as black holes and believe all the unscientific information that may exist at the moment. First of all, we need to dispel the most common myth that black holes can suck in all the matter and objects around them, and as they do so, they grow larger and absorb more and more. None of this is entirely true. Yes, indeed, they can absorb cosmic bodies and matter, but only those that are at a certain distance from the hole itself. Apart from their powerful gravity, they are not much different from ordinary stars with gigantic mass. Even when our Sun turns into a black hole, it will only be able to suck in objects located at a short distance, and all the planets will remain rotating in their usual orbits.
Turning to the theory of relativity, we can conclude that all objects with strong gravity can influence the curvature of time and space. In addition, the greater the body mass, the stronger the distortion will be. So, quite recently, scientists were able to see this in practice, when they could contemplate other objects that should have been inaccessible to our eyes due to huge cosmic bodies such as galaxies or black holes. All this is possible due to the fact that light rays passing nearby from a black hole or other body are very strongly bent under the influence of their gravity. This type of distortion allows scientists to look much further into outer space. But with such studies it is very difficult to determine the real location of the body being studied.
Black holes don't appear out of nowhere; they are formed by the explosion of supermassive stars. Moreover, in order for a black hole to form, the mass of the exploded star must be at least ten times greater than the mass of the Sun. Each star exists due to thermonuclear reactions that take place inside the star. In this case, a hydrogen alloy is released during the fusion process, but it cannot leave the star’s area of influence, since its gravity attracts the hydrogen back. This whole process allows stars to exist. Hydrogen synthesis and star gravity are fairly well-functioning mechanisms, but disruption of this balance can lead to a star explosion. In most cases, it is caused by the exhaustion of nuclear fuel.
Depending on the mass of the star, several scenarios for their development after the explosion are possible. Thus, massive stars form the field of a supernova explosion, and most of them remain behind the core of the former star; astronauts call such objects White Dwarfs. In most cases, a gas cloud forms around these bodies, which is held in place by the gravity of the dwarf. Another path for the development of supermassive stars is also possible, in which the resulting black hole will very strongly attract all the matter of the star to its center, which will lead to its strong compression.
Such compressed bodies are called neutron stars. In the rarest cases, after the explosion of a star, the formation of a black hole in our accepted understanding of this phenomenon is possible. But for a hole to be created, the mass of the star must be simply gigantic. In this case, when the balance of nuclear reactions is disrupted, the gravity of the star simply goes crazy. At the same time, it begins to actively collapse, after which it becomes only a point in space. In other words, we can say that the star as a physical object ceases to exist. Despite the fact that it disappears, a black hole with the same gravity and mass is formed behind it.
It is the collapse of stars that leads to the fact that they completely disappear, and in their place a black hole is formed with the same physical properties as the disappeared star. The only difference is the greater degree of compression of the hole than the volume of the star. The most important feature of all black holes is their singularity, which determines its center. This area defies all laws of physics, matter and space, which cease to exist. To understand the concept of singularity, we can say that this is a barrier that is called the cosmic event horizon. It is also the outer boundary of the black hole. The singularity can be called the point of no return, since it is there that the gigantic gravitational force of the hole begins to act. Even the light that crosses this barrier is unable to escape.
The event horizon has such an attractive effect that attracts all bodies at the speed of light; as you approach the black hole itself, the speed indicators increase even more. That is why all objects that fall within the range of this force are doomed to be sucked into the hole. It should be noted that such forces are capable of modifying a body caught by the action of such attraction, after which they stretch into a thin string, and then completely cease to exist in space.
The distance between the event horizon and the singularity can vary; this space is called the Schwarzschild radius. That is why the larger the size of the black hole, the larger the range of action will be. For example, we can say that a black hole that was as massive as our Sun would have a Schwarzschild radius of three kilometers. Accordingly, large black holes have a larger range.
Finding black holes is a rather difficult process because light cannot escape from them. Therefore, the search and definition are based only on indirect evidence of their existence. The simplest method that scientists use to find them is to search for them by finding places in dark space if they have a large mass. In most cases, astronomers manage to find black holes in binary star systems or in the centers of galaxies.
Most astronomers are inclined to believe that there is also a super-powerful black hole at the center of our galaxy. This statement begs the question, will this hole be able to swallow everything in our galaxy? In reality this is impossible, since the hole itself has the same mass as the stars, because it is created from the star. Moreover, all the calculations of scientists do not foretell any global events related to this object. Moreover, for another billions of years, the cosmic bodies of our galaxy will quietly rotate around this black hole without any changes. Evidence of the existence of a hole in the center of the Milky Way can be obtained from X-ray waves recorded by scientists. And most astronomers are inclined to believe that black holes actively emit them in huge quantities.
Quite often in our galaxy there are star systems consisting of two stars, and often one of them can become a black hole. In this version, the black hole absorbs all bodies in its path, while matter begins to rotate around it, due to which the so-called acceleration disk is formed. A special feature is that it increases the rotation speed and moves closer to the center. It is the matter that falls into the middle of the black hole that emits X-rays, and the matter itself is destroyed.
Binary star systems are the very first candidates for black hole status. In such systems it is most easy to find a black hole; due to the volume of the visible star, the indicators of the invisible brother can be calculated. Currently, the very first candidate for the status of a black hole may be a star from the constellation Cygnus, which actively emits X-rays.
Concluding from all of the above about black holes, we can say that they are not such dangerous phenomena, of course, in the case of close proximity they are the most powerful objects in outer space due to the force of gravity. Therefore, we can say that they are not particularly different from other bodies; their main feature is a strong gravitational field.
A huge number of theories have been proposed regarding the purpose of black holes, some of which were even absurd. Thus, according to one of them, scientists believed that black holes can give birth to new galaxies. This theory is based on the fact that our world is a fairly favorable place for the origin of life, but if one of the factors changes, life would be impossible. Because of this, the singularity and peculiarities of changes in physical properties in black holes can give rise to a completely new Universe, which will be significantly different from ours. But this is only a theory and a rather weak one due to the fact that there is no evidence of such an effect of black holes.
As for black holes, not only can they absorb matter, but they can also evaporate. A similar phenomenon was proven several decades ago. This evaporation can cause the black hole to lose all its mass, and then disappear altogether.
All this is the smallest piece of information about black holes that you can find out on the portal website. We also have a huge amount of interesting information about other cosmic phenomena.
BLACK HOLE
a region in space resulting from the complete gravitational collapse of matter, in which the gravitational attraction is so strong that neither matter, nor light, nor other information carriers can leave it. Therefore, the interior of a black hole is not causally connected to the rest of the Universe; Physical processes occurring inside a black hole cannot influence processes outside it. A black hole is surrounded by a surface with the property of a unidirectional membrane: matter and radiation freely fall through it into the black hole, but nothing can escape from there. This surface is called the "event horizon". Since there are still only indirect indications of the existence of black holes at distances of thousands of light years from the Earth, our further presentation is based mainly on theoretical results. Black holes, predicted by the general theory of relativity (the theory of gravity proposed by Einstein in 1915) and other, more modern theories of gravity, were mathematically substantiated by R. Oppenheimer and H. Snyder in 1939. But the properties of space and time in the vicinity of these objects turned out to be so unusual, that astronomers and physicists did not take them seriously for 25 years. However, astronomical discoveries in the mid-1960s brought black holes to the surface as a possible physical reality. Their discovery and study can fundamentally change our ideas about space and time.
Formation of black holes. While thermonuclear reactions occur in the bowels of the star, they maintain high temperature and pressure, preventing the star from collapsing under the influence of its own gravity. However, over time, the nuclear fuel is depleted, and the star begins to shrink. Calculations show that if the mass of a star does not exceed three solar masses, then it will win the “battle with gravity”: its gravitational collapse will be stopped by the pressure of “degenerate” matter, and the star will forever turn into a white dwarf or neutron star. But if the mass of the star is more than three solar, then nothing can stop its catastrophic collapse and it will quickly go under the event horizon, becoming a black hole. For a spherical black hole of mass M, the event horizon forms a sphere with a circle at the equator 2p times larger than the “gravitational radius” of the black hole RG = 2GM/c2, where c is the speed of light and G is the gravitational constant. A black hole with a mass of 3 solar masses has a gravitational radius of 8.8 km.
If an astronomer observes a star at the moment of its transformation into a black hole, then at first he will see how the star is compressing faster and faster, but as its surface approaches the gravitational radius, the compression will begin to slow down until it stops completely. At the same time, the light coming from the star will weaken and redden until it goes out completely. This happens because, in the fight against the gigantic force of gravity, the light loses energy and it takes more and more time for it to reach the observer. When the star's surface reaches the gravitational radius, the light that leaves it will take an infinite amount of time to reach the observer (and the photons will lose all their energy). Consequently, the astronomer will never wait for this moment, much less see what is happening to the star below the event horizon. But theoretically this process can be studied. Calculations of idealized spherical collapse show that in a short time the star collapses to a point where infinitely high values of density and gravity are achieved. Such a point is called "singularity". Moreover, general mathematical analysis shows that if an event horizon has arisen, then even a non-spherical collapse leads to a singularity. However, all this is true only if general relativity applies down to very small spatial scales, which we are not yet sure of. Quantum laws operate in the microworld, but the quantum theory of gravity has not yet been created. It is clear that quantum effects cannot stop the collapse of a star into a black hole, but they could prevent the appearance of a singularity. The modern theory of stellar evolution and our knowledge of the stellar population of the Galaxy indicate that among its 100 billion stars there should be about 100 million black holes formed during the collapse of the most massive stars. In addition, black holes of very large masses can be located in the cores of large galaxies, including ours. As already noted, in our era, only a mass more than three times the solar mass can become a black hole. However, immediately after the Big Bang, from which approx. 15 billion years ago, the expansion of the Universe began, black holes of any mass could be born. The smallest of them, due to quantum effects, should have evaporated, losing their mass in the form of radiation and particle flows. But “primary black holes” with a mass of more than 1015 g could survive to this day. All calculations of stellar collapse are made under the assumption of a slight deviation from spherical symmetry and show that an event horizon is always formed. However, with a strong deviation from spherical symmetry, the collapse of a star can lead to the formation of a region with infinitely strong gravity, but not surrounded by an event horizon; it is called the "naked singularity". This is no longer a black hole in the sense we discussed above. Physical laws near a naked singularity can take a very unexpected form. Currently, a naked singularity is considered an unlikely object, while most astrophysicists believe in the existence of black holes.
Properties of black holes. To an outside observer, the structure of a black hole looks extremely simple. During the collapse of a star into a black hole in a small fraction of a second (according to a remote observer's clock), all its external features associated with the inhomogeneity of the original star are emitted in the form of gravitational and electromagnetic waves. The resulting stationary black hole “forgets” all information about the original star, except for three quantities: total mass, angular momentum (associated with rotation) and electric charge. By studying a black hole, it is no longer possible to know whether the original star consisted of matter or antimatter, whether it had the shape of a cigar or a pancake, etc. Under real astrophysical conditions, a charged black hole will attract particles of the opposite sign from the interstellar medium, and its charge will quickly become zero. The remaining stationary object will either be a non-rotating "Schwarzschild black hole", which is characterized only by mass, or a rotating "Kerr black hole", which is characterized by mass and angular momentum. The uniqueness of the above types of stationary black holes was proven within the framework of the general theory of relativity by W. Israel, B. Carter, S. Hawking and D. Robinson. According to the general theory of relativity, space and time are curved by the gravitational field of massive bodies, with the greatest curvature occurring near black holes. When physicists talk about intervals of time and space, they mean numbers read from some physical clock or ruler. For example, the role of a clock can be played by a molecule with a certain vibration frequency, the number of which between two events can be called a “time interval.” It is remarkable that gravity affects all physical systems in the same way: all clocks show that time is slowing down, and all rulers show that space is stretching near a black hole. This means that the black hole bends the geometry of space and time around itself. Far from the black hole, this curvature is small, but close to it it is so large that light rays can move around it in a circle. Far from a black hole, its gravitational field is exactly described by Newton's theory for a body of the same mass, but close to it, gravity becomes much stronger than Newton's theory predicts. Any body falling into a black hole will be torn apart long before crossing the event horizon by powerful tidal gravitational forces arising from differences in gravity at different distances from the center. A black hole is always ready to absorb matter or radiation, thereby increasing its mass. Its interaction with the outside world is determined by a simple Hawking principle: the area of the event horizon of a black hole never decreases, unless one takes into account the quantum production of particles. J. Bekenstein in 1973 suggested that black holes obey the same physical laws as physical bodies that emit and absorb radiation (the “absolutely black body” model). Influenced by this idea, Hawking showed in 1974 that black holes can emit matter and radiation, but this will only be noticeable if the mass of the black hole itself is relatively small. Such black holes could be born immediately after the Big Bang, which began the expansion of the Universe. The masses of these primary black holes should be no more than 1015 g (like a small asteroid), and their size should be 10-15 m (like a proton or neutron). The powerful gravitational field near a black hole produces particle-antiparticle pairs; one of the particles of each pair is absorbed by the hole, and the second is emitted outward. A black hole with a mass of 1015 g should behave like a body with a temperature of 1011 K. The idea of \u200b\u200b“evaporation” of black holes completely contradicts the classical concept of them as bodies that are not capable of radiating.
Search for black holes. Calculations within the framework of Einstein's general theory of relativity only indicate the possibility of the existence of black holes, but do not at all prove their presence in the real world; the discovery of a real black hole would be an important step in the development of physics. Finding isolated black holes in space is hopelessly difficult: we will not be able to notice a small dark object against the background of cosmic blackness. But there is hope to detect a black hole by its interaction with surrounding astronomical bodies, by its characteristic influence on them. Supermassive black holes can reside in the centers of galaxies, continuously devouring stars there. Concentrated around the black hole, the stars should form central brightness peaks in the galactic nuclei; Their search is now actively underway. Another search method is to measure the speed of stars and gas around a central object in the galaxy. If their distance from the central object is known, then its mass and average density can be calculated. If it significantly exceeds the density possible for star clusters, then it is believed that it is a black hole. Using this method, in 1996 J. Moran and his colleagues determined that in the center of the galaxy NGC 4258 there is probably a black hole with a mass of 40 million solar. The most promising is to search for a black hole in binary systems, where it, paired with a normal star, can orbit around a common center of mass. By the periodic Doppler shift of lines in the spectrum of a star, one can understand that it is orbiting in tandem with a certain body and even estimate the mass of the latter. If this mass exceeds 3 solar masses, and the radiation of the body itself cannot be detected, then it is very possible that it is a black hole. In a compact binary system, the black hole can capture gas from the surface of a normal star. Moving in orbit around the black hole, this gas forms a disk and, as it spirals toward the black hole, it becomes very hot and becomes a source of powerful X-ray radiation. Rapid fluctuations in this radiation should indicate that the gas is rapidly moving in a small radius orbit around a tiny, massive object. Since the 1970s, several X-ray sources have been discovered in binary systems with clear signs of black holes. The most promising is the X-ray binary V 404 Cygni, the mass of the invisible component of which is estimated to be no less than 6 solar masses. Other remarkable black hole candidates are in the X-ray binaries Cygnus X-1, LMCX-3, V 616 Monoceros, QZ Vulpeculae, and the X-ray novae Ophiuchus 1977, Mukha 1981, and Scorpius 1994. With the exception of LMCX-3, located in the Large Magellanic Cloud, all of them are located in our Galaxy at distances of about 8000 light years. years from Earth.
see also
COSMOLOGY;
GRAVITY;
GRAVITATIONAL COLLAPSE;
RELATIVITY;
EXTRA-ATMOSPHERE ASTRONOMY.
LITERATURE
Cherepashchuk A.M. Masses of black holes in binary systems. Advances in Physical Sciences, vol. 166, p. 809, 1996
Collier's Encyclopedia. - Open Society. 2000 .
Synonyms:See what a “BLACK HOLE” is in other dictionaries:
BLACK HOLE, a localized area of outer space from which neither matter nor radiation can escape, in other words, the first cosmic speed exceeds the speed of light. The boundary of this area is called the event horizon.... ... Scientific and technical encyclopedic dictionary
Cosmic an object that arises as a result of the compression of a body by gravity. forces to sizes smaller than its gravitational radius rg=2g/c2 (where M is the mass of the body, G is the gravitational constant, c is the numerical value of the speed of light). Prediction about the existence of... ... Physical encyclopedia
After the nuclear fuel reserves are depleted, thermonuclear reactions stop and the star begins to shrink under its own weight. If it has a fairly large mass, the core is compressed so much that a black hole is formed. These objects have colossal mass with a small volume, and their gravity is so strong that even light cannot escape its attraction.
If the Sun ever becomes such a body, then it must be compressed to a radius of only 9 km, and the Earth must be compressed to the size of a pea.
In it, density and gravity take on infinite values. But all this is true for the ordinary, macrocosm. The microworld does not yet have its own theory of gravity.
What's inside a black hole
It has been established that there is a singularity inside the black hole. We don't yet have the tools to study these objects, but we do have a couple of fascinating videos :)
- Time passes slower near black holes than away from them. If you observe an object thrown at this object, the movement of the object will slow down and its visibility will be weakened. At the end he will stop and become invisible. But if the observer himself jumps there, he will instantly fall into the center of the hole, and gravitational forces will tear him apart instantly. And he will see the entire life of the universe, from birth to death.
- An interesting property is after overcoming the event horizon: the more you resist the gravity of the black hole and strive to fly further away, the faster you will fall into it. It’s hard to imagine this, you must agree...
- It doesn’t matter what the body was like before compression, after this process only three of its parameters can be examined. These are electric charge, total mass and angular momentum. It is impossible to establish the initial parameters of a black hole - its shape, color, composition of matter.
- Everything that falls beyond the event horizon necessarily falls towards the center, where there is a singularity that has infinite density. This is a place where the laws of physics and classical concepts of space and time no longer apply.
- Stephen Hawking was able to discover the evaporation of black holes. Large holes will evaporate for a very long time - tens and hundreds of billions of years, and microscopic ones - in a fraction of a second. The hypothetical evaporation, or emission of photons, is called Hawking radiation. This process has a purely theoretical justification. According to the theory, black holes formed at the birth of the Universe and having a mass of 10 12 kg should completely evaporate by our time. Since the intensity of evaporation increases with decreasing size, this process should end in an explosion. Astronomers have not yet observed such explosions.
- The classical theory of gravity suggests that a black hole can neither be reduced nor destroyed. It can only increase. It follows from this that the information that gets inside is inaccessible to an outside observer.
- No one knows for sure what we will see when approaching a black hole. But it is quite possible that she is not that black. Matter flying onto its surface accelerates and heats up, and must glow before diving below the event horizon. Therefore, in front of us there will not be a round dark cutout in space, but a shining halo, a little like the sun at the moment of its total eclipse.
Supermassive black holes
All galaxies have black holes at their centers, including ours. Such conclusions were made based on observations of the movement of interstellar gas and nearby stars. Calculations show that objects in the center of the galaxy should have enormous masses but small sizes. It turns out that any center is a black hole. And their masses are millions and billions of solar masses. All observed stellar systems with the properties of black holes have masses of 4 – 16 solar.
Many signals - the vibrations of stars, some others - are translated into sound form. This is how eerie the sound of two black holes merging looks:
How to find them
It is possible to detect a black hole if it is part of a binary system. For example, in a binary system, one of the stars explodes, turning into a The remaining star will be affected by the gravity of its neighbor, therefore matter from the star will flow into the black hole (it will literally “devour” the star ).
The matter from the star will spin into a spiral around the black hole, causing it to become strongly densified and heated. Heating will continue until wave radiation appears in the X-ray range, by the nature of which it is possible to understand the parameters of the object. Also, a black hole, flying near a star, deflects it from its normal trajectory with its colossal gravity, thereby revealing itself. Black holes without a star partner also exist in theoretical calculations.
How they study
Black holes are studied mainly through mathematical modeling and physics. If theoretical calculations are consistent with observations and do not contradict proven facts, the hypothesis turns into a generally accepted theory. Here is a video where this is discussed in detail:
Date of publication: 09/27/2012
Most people have a vague or incorrect idea of what black holes are. Meanwhile, these are such global and powerful objects of the Universe, in comparison with which our Planet and our entire life are nothing.
Essence
This is a cosmic object with such enormous gravity that it absorbs everything that falls within its boundaries. Essentially, a black hole is an object that does not even let out light and bends space-time. Even time moves slower near black holes.
In fact, the existence of black holes is just a theory (and a little practice). Scientists have assumptions and practical experience, but have not yet been able to closely study black holes. Therefore, all objects that fit this description are conventionally called black holes. Black holes have been little studied, and therefore many questions remain unresolved.
Any black hole has an event horizon - that boundary after which nothing can escape. Moreover, the closer an object is to a black hole, the slower it moves.
Education
There are several types and methods of formation of black holes:
- the formation of black holes as a result of the formation of the Universe. Such black holes appeared immediately after the Big Bang.
- dying stars. When a star loses its energy and thermonuclear reactions stop, the star begins to shrink. Depending on the degree of compression, neutron stars, white dwarfs and, in fact, black holes are distinguished.
- obtained through experiment. For example, a quantum black hole can be created in a collider.
Versions
Many scientists are inclined to believe that black holes eject all the absorbed matter elsewhere. Those. There must be “white holes” that operate on a different principle. If you can get into a black hole, but cannot get out, then, on the contrary, you cannot get into a white hole. The main argument of scientists is the sharp and powerful bursts of energy recorded in space.
Proponents of string theory generally created their own model of a black hole, which does not destroy information. Their theory is called "Fuzzball" - it allows us to answer questions related to the singularity and the disappearance of information.
What is singularity and disappearance of information? A singularity is a point in space characterized by infinite pressure and density. Many people are confused by the fact of singularity, because physicists cannot work with infinite numbers. Many are sure that there is a singularity in a black hole, but its properties are described very superficially.
In simple terms, all problems and misunderstandings arise from the relationship between quantum mechanics and gravity. So far, scientists cannot create a theory that unites them. And that is why problems arise with a black hole. After all, a black hole seems to destroy information, but at the same time the foundations of quantum mechanics are violated. Although quite recently S. Hawking seemed to have resolved this issue, stating that information in black holes is not destroyed after all.
Stereotypes
Firstly, black holes cannot exist indefinitely. And all thanks to Hawking evaporation. Therefore, there is no need to think that black holes will sooner or later swallow the Universe.
Secondly, our Sun will not become a black hole. Since the mass of our star will not be enough. Our sun is more likely to turn into a white dwarf (and that’s not a fact).
Thirdly, the Large Hadron Collider will not destroy our Earth by creating a black hole. Even if they deliberately create a black hole and “release” it, then due to its small size, it will consume our planet for a very, very long time.
Fourthly, you don’t need to think that a black hole is a “hole” in space. A black hole is a spherical object. Hence the majority of opinions that black holes lead to a parallel Universe. However, this fact has not yet been proven.
Fifthly, a black hole has no color. It is detected either by X-ray radiation or against the background of other galaxies and stars (lens effect).
Due to the fact that people often confuse black holes with wormholes (which actually exist), these concepts are not distinguished among ordinary people. A wormhole really allows you to move in space and time, but so far only in theory.
Complex things in simple terms
It is difficult to describe such a phenomenon as a black hole in simple language. If you consider yourself a techie versed in the exact sciences, then I advise you to read the works of scientists directly. If you want to learn more about this phenomenon, then read the works of Stephen Hawking. He did a lot for science, and especially in the field of black holes. The evaporation of black holes is named after him. He is a supporter of the pedagogical approach, and therefore all his works will be understandable even to the average person.
Books:
- “Black Holes and Young Universes” 1993.
- “The World in a Nutshell 2001.”
- “The Brief History of the Universe 2005”.
I especially want to recommend his popular science films, which will tell you in an understandable language not only about black holes, but also about the Universe in general:
- “Stephen Hawking's Universe” - a series of 6 episodes.
- “Deep into the Universe with Stephen Hawking” - a series of 3 episodes.
All these films have been translated into Russian and are often shown on Discovery channels.
Thank you for your attention!
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Predicts that in a black hole there is a singularity, a place where tidal forces become infinitely large, and once you pass the event horizon, you can't go anywhere else but the singularity. Accordingly, it is better not to use general relativity in these places - it simply does not work. To tell what happens inside a black hole, we need a theory of quantum gravity. It is generally accepted that this theory will replace the singularity with something else.
How are black holes formed?
We currently know of four different ways black holes form. Best understood is associated with stellar collapse. A large enough star will form a black hole after its nuclear fusion stops, because everything that could already be fused has been fused. When the pressure created by the synthesis stops, the substance begins to fall towards its own gravitational center, becoming increasingly dense. Eventually, it becomes so dense that nothing can overcome the gravitational influence on the surface of the star: this is how a black hole is born. These black holes are called "solar mass black holes" and are the most common.
The next common type of black hole is the “supermassive black hole,” which can be found at the centers of many galaxies and has masses about a billion times greater than solar-mass black holes. It is not yet known for certain how exactly they are formed. They are believed to have once started out as solar-mass black holes that, in densely populated galactic centers, swallowed up many other stars and grew. However, they appear to absorb matter faster than this simple idea suggests, and exactly how they do this is still a matter of research.
A more controversial idea has been primordial black holes, which could have been formed by virtually any mass in large density fluctuations in the early Universe. While this is possible, it is quite difficult to find a model that produces them without creating an excessive amount of them.
Finally, there is a very speculative idea that the Large Hadron Collider could produce tiny black holes with masses close to the mass of the Higgs boson. This only works if our Universe has extra dimensions. So far there has been no evidence to support this theory.
How do we know that black holes exist?
We have a lot of observational evidence for the existence of compact objects with large masses that do not emit light. These objects reveal themselves through gravitational attraction, for example due to the movement of other stars or gas clouds around them. They also create gravitational lensing. We know that these objects do not have a solid surface. This follows from observation because matter falling onto an object with a surface should cause the emission of more particles than matter falling through the horizon.
Why did Hawking say last year that black holes don't exist?
He meant that black holes do not have an eternal event horizon, but only a temporary apparent horizon (see point one). In a strict sense, only the event horizon is considered a black hole.
How do black holes emit radiation?
Black holes emit radiation due to quantum effects. It is important to note that these are quantum effects of matter, not quantum effects of gravity. The dynamical spacetime of a collapsing black hole changes the very definition of a particle. Like the flow of time that becomes distorted near a black hole, the concept of particles is too dependent on the observer. In particular, when an observer falling into a black hole thinks that he is falling into a vacuum, an observer far from the black hole thinks that it is not a vacuum, but a space full of particles. It is the stretching of space-time that causes this effect.
First discovered by Stephen Hawking, the radiation emitted by a black hole is called “Hawking radiation.” This radiation has a temperature inversely proportional to the mass of the black hole: the smaller the black hole, the higher the temperature. Stellar and supermassive black holes that we know have temperatures well below the microwave background temperature and are therefore not observable.
What is an information paradox?
The information loss paradox is caused by Hawking radiation. This radiation is purely thermal, that is, it is random and has only temperature among certain properties. The radiation itself does not contain any information about how the black hole formed. But when a black hole emits radiation, it loses mass and shrinks. All this is completely independent of the matter that became part of the black hole or from which it was formed. It turns out that knowing only the final state of evaporation it is impossible to say from what the black hole was formed. This process is "irreversible" - and the catch is that there is no such process in quantum mechanics.
It turns out that the evaporation of a black hole is incompatible with quantum theory as we know it, and something needs to be done about it. Somehow resolve the inconsistency. Most physicists believe the solution is that Hawking radiation must somehow contain information.
What does Hawking propose to solve the black hole information paradox?
The idea is that black holes must have a way to store information, which has not yet been accepted. The information is stored at the black hole's horizon and can cause tiny particle displacements in the Hawking radiation. These tiny displacements may contain information about the matter trapped inside. The exact details of this process are currently unclear. Scientists are awaiting a more detailed technical paper from Stephen Hawking, Malcolm Perry and Andrew Strominger. They say it will appear at the end of September.
At the moment, we are sure that black holes exist, we know where they are, how they are formed and what they will become in the end. But the details of where the information entering them goes remains one of the biggest mysteries of the Universe.
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