In order for a black hole to form, it is necessary to compress a 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) 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 galactic core ( M=10 10 M sun) 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 the 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, maintaining 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 a size, will already compress 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”. This 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.
Evolution of stars
Black holes form at the final stages of the evolution of massive stars. In the depths of ordinary stars, thermonuclear reactions occur, enormous energy is released and a high temperature is maintained (tens and hundreds of millions of degrees). Gravitational forces tend to compress the star, and the pressure forces of hot gas and radiation resist this compression. Therefore, the star is in hydrostatic equilibrium.
In addition, a star can exist in thermal equilibrium, when the energy release due to thermonuclear reactions at 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 disrupted. 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 compression) in absolute value is always twice the thermal energy. 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. For a star, the opposite is true: the more energy it loses in the form of radiation, the higher the temperature at its center becomes.
This strange, at first glance, feature has a simple explanation: the star, as it radiates, slowly contracts. During compression, potential energy is converted into kinetic energy of falling layers of the star, and its interior heats up. Moreover, the thermal energy acquired by the star as a result of compression is twice as much as the energy lost in the form of radiation. As a result, the temperature of the star’s interior increases, and continuous thermonuclear synthesis of chemical elements occurs. For example, the reaction of converting hydrogen into helium in the current Sun occurs at a temperature of 15 million degrees. When, after 4 billion years, at the center of the Sun, all hydrogen turns into helium, the further synthesis of carbon atoms from helium atoms will require a much higher temperature, about 100 million degrees (the electrical charge of helium nuclei is twice that of hydrogen nuclei, and to bring the nuclei closer together helium at a distance of 10–13 cm requires a much higher temperature). It is precisely this temperature that will be ensured due to the negative heat capacity of the Sun by the time the thermonuclear reaction of converting helium into carbon is ignited in its depths.
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, the thermonuclear fusion of chemical elements may cease 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 motion 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 compression. 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. Consequently, gravitational energy is not released as additional heat. Therefore, the temperature in the evolving degenerate core does not increase, which leads to the interruption of the chain of thermonuclear reactions.
The outer hydrogen shell, unaffected by thermonuclear reactions, separates from the star's core 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 low-mass star is a white dwarf - an object with a radius on the order of the Earth's radius (~10 4 km), a mass of less than 1.4 M sun and an average density of about a ton per cubic centimeter. White dwarfs are observed in large numbers. Their total number in the Galaxy reaches 10 10, that is, about 10% of the total mass of the observable matter of the Galaxy.
Thermonuclear burning in a degenerate white dwarf can be unstable and lead to a nuclear explosion of 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 supernovae, which have no hydrogen lines in their spectrum, but only lines of helium, carbon, oxygen and other heavy elements.
Neutron stars
If the star’s core 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 counteract the forces of gravity decreases, and the star experiences gravitational collapse. During collapse, electrons are captured by protons, and neutronization of the substance occurs. This leads to the formation of a neutron star from a massive degenerate core.
If the initial mass of the star's core exceeds 1.4 M sun, then a high temperature is reached in the core, and electron degeneration 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 depths increases, and there is a continuous chain of thermonuclear reactions converting 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 nuclei of elements heavier than iron no longer occurs with the release, but with the absorption of energy. Therefore, if the mass of the star's core, consisting mainly of iron group elements, 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, gravitational collapse of the core occurs, as a result of which the outer hydrogen shell of the star is shed, 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 break apart into neutrons and protons. Protons absorb electrons and turn into neutrons, emitting neutrinos. Neutrons, according to the quantum mechanical Pauli principle, with strong compression begin to effectively repel each other.
When the mass of the collapsing core is less than 3 M sun, neutron speeds are significantly less than the speed of light and the elasticity of matter due to the effective repulsion of neutrons can balance the gravitational forces and lead to the formation of a stable neutron star.
The possibility of the existence of neutron stars was first 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, collapses into a black hole. The collapse of a neutron star into a black hole is also facilitated by the reverse fall of part of the star's shell, ejected during a supernova explosion.
A neutron star typically rotates rapidly because the normal star that gave birth to it can have significant angular momentum. When a star's core 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 angular momentum, the speed of axial rotation must increase sharply. For example, if the Sun, rotating 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 pulses of radio emission 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 X-ray pulsar and type 1 X-ray burster.
One cannot expect strictly periodic pulsations of radiation from a black hole, since the black hole has no observable surface and no magnetic field. As physicists often say, black holes do not have “hair” - all fields and all inhomogeneities near the event horizon are emitted when the black hole is formed from collapsing matter in the form of a stream of gravitational waves. As a result, the resulting black hole has only three characteristics: mass, angular momentum and electric charge. All individual properties of the collapsing substance are forgotten during the formation of a black hole: for example, black holes formed from iron and from water have, other things being equal, the same characteristics.
As predicted by the General Theory of Relativity (GR), 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 densities of matter achieved during the compression of such a massive star core, the main contribution to the energy density is no longer made by the rest energy of the particles, but by the energy of their movement and interaction . It turns out that in general relativity the pressure of a substance 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 substance. 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 formed in our era (for example, the black hole in the Cygnus X-1 system), strictly speaking, are not one hundred percent black holes, since due to relativistic time dilation for a distant observer, their event horizons still have not formed. The surfaces of such collapsing stars appear to an observer on Earth as frozen, endlessly approaching their event horizons.
In order for black holes from such collapsing objects to finally form, we must wait the entire infinitely long time of the existence of our Universe. It should be emphasized, however, that already in the first seconds of 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.
Have you ever seen a floor being vacuumed? If so, have you noticed how the vacuum cleaner sucks up dust and small debris like scraps of paper? Of course they noticed. Black holes do much the same thing as a vacuum cleaner, but instead of dust, they prefer to suck in larger objects: stars and planets. However, they will not disdain cosmic dust either.
How do black holes appear?
To understand where black holes come from, it would be nice to know what light pressure is. It turns out that light falling on objects puts pressure on them. For example, if we light a light bulb in a dark room, then an additional light pressure force will begin to act on all illuminated objects. This force is very small, and in everyday life we, of course, will never be able to feel it. The reason is that a light bulb is a very weak light source. (In laboratory conditions, the light pressure of a light bulb can still be measured; the Russian physicist P. N. Lebedev was the first to do this) With stars, the situation is different. While the star is young and shining brightly, three forces are fighting inside it. On the one hand, the force of gravity, which tends to compress the star into a point, pulls the outer layers inward towards the core. On the other hand, there is the force of light pressure and the pressure force of hot gas, tending to inflate the star. The light produced in the star's core is so intense that it pushes away the outer layers of the star and balances the force of gravity pulling them toward the center. As a star ages, its core produces less and less light. This happens because during the life of a star, its entire supply of hydrogen burns out, we have already written about this. If the star is very large, 20 times heavier than the Sun, then its outer shells are very large in mass. Therefore, in a heavy star, the outer layers begin to move closer and closer to the core, and the entire star begins to contract. At the same time, the gravitational force on the surface of the contracting star increases. The more a star contracts, the more strongly it begins to attract the surrounding matter. Eventually, the star's gravity becomes so monstrously strong that even the light it emits cannot escape. At this moment the star becomes a black hole. It no longer emits anything, but only absorbs everything that is nearby, including light. Not a single ray of light comes from it, so no one can see it, and that’s why it’s called a black hole: everything gets sucked into it and never comes back.
What does a black hole look like?
If you and I were next to a black hole, we would see a fairly large luminous disk rotating around a small, completely black region of space. This black region is a black hole. And the luminous disk around it is matter falling into the black hole. Such a disk is called an accretion disk. The gravity of a black hole is very strong, so the matter sucked inside moves with very high acceleration and because of this it begins to radiate. By studying the light coming from such a disk, astronomers can learn a lot about the black hole itself. Another indirect sign of the existence of a black hole is the unusual movement of stars around a certain region of space. The hole's gravity forces nearby stars to move in elliptical orbits. Such movements of stars are also recorded by astronomers.
Now the attention of scientists is focused on the black hole located at the center of our galaxy. The fact is that a cloud of hydrogen with a mass about 3 times that of Earth is approaching the black hole. This cloud has already begun to change its shape due to the gravity of the black hole, in the coming years it will stretch even more and will be pulled inside the black hole.
We will never be able to see the processes occurring inside a black hole, so we can only be content with observing the disk around the black hole. But a lot of interesting things await us here too. Perhaps the most interesting phenomenon is the formation of ultrafast jets of matter escaping from the center of this disk. The mechanism of this phenomenon remains to be elucidated, and it is quite possible that one of you will create a theory for the formation of such jets. For now, we can only register the X-ray flashes that accompany such “shots.”
This video shows how a black hole gradually captures material from a nearby star. In this case, an accretion disk is formed around the black hole, and part of its matter is ejected into space at enormous speeds. This generates a large amount of X-ray radiation, which is picked up by a satellite moving around the Earth.
How does a black hole work?
A black hole can be divided into three main parts. The outer part, being in which you can still avoid falling into a black hole if you move at very high speed. Deeper than the outer part there is an event horizon - this is an imaginary boundary, after crossing which the body loses all hope of returning from the black hole. Everything that is beyond the event horizon cannot be seen from the outside, because due to strong gravity, even light moving from inside will not be able to fly beyond it. It is believed that at the very center of a black hole there is a singularity - a region of space of a tiny volume in which a huge mass is concentrated - the heart of the black hole.
Is it possible to fly up to a black hole?
At a great distance, the attraction of a black hole is exactly the same as the attraction of an ordinary star with the same mass as the black hole. As you approach the event horizon, the attraction will grow stronger and stronger. Therefore, you can fly up to a black hole, but it is better to stay away from it so that you can return back. Astronomers had to watch how a black hole sucked a nearby star inside. You can see what it looked like in this video:
Will our Sun turn into a black hole?
No, it won't turn. The mass of the Sun is too small for this. Calculations show that in order to become a black hole, a star must be at least 4 times more massive than the Sun. Instead, the Sun will become a red giant and inflate to about the size of Earth's orbit before shedding its outer shell and becoming a white dwarf. We will definitely tell you more about the evolution of the Sun.
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 speed rates 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 do not appear out of nowhere; they are formed as a result of 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, since 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 scientists’ calculations 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 come from the 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, it is possible to calculate the indicators of its invisible brother. 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 site. We also have a huge amount of interesting information about other cosmic phenomena.
The concept of a black hole is known to everyone - from schoolchildren to the elderly; it is used in science and fiction literature, in the yellow media and at scientific conferences. But what exactly such holes are is not known to everyone.
From the history of black holes
1783 The first hypothesis of the existence of such a phenomenon as a black hole was put forward in 1783 by the English scientist John Michell. In his theory, he combined two of Newton's creations - optics and mechanics. Michell's idea was this: if light is a stream of tiny particles, then, like all other bodies, the particles should experience the attraction of a gravitational field. It turns out that the more massive the star, the more difficult it is for light to resist its attraction. 13 years after Michell, the French astronomer and mathematician Laplace put forward (most likely independently of his British colleague) a similar theory.
1915 However, all their works remained unclaimed until the beginning of the 20th century. In 1915, Albert Einstein published the General Theory of Relativity and showed that gravity is the curvature of spacetime caused by matter, and a few months later, German astronomer and theoretical physicist Karl Schwarzschild used it to solve a specific astronomical problem. He explored the structure of curved space-time around the Sun and rediscovered the phenomenon of black holes.
(John Wheeler coined the term "Black holes")
1967 American physicist John Wheeler outlined a space that can be crumpled, like a piece of paper, into an infinitesimal point and designated it with the term “Black Hole”.
1974 British physicist Stephen Hawking proved that black holes, although they absorb matter without return, can emit radiation and eventually evaporate. This phenomenon is called “Hawking radiation”.
2013 The latest research into pulsars and quasars, as well as the discovery of cosmic microwave background radiation, has finally made it possible to describe the very concept of black holes. In 2013, the gas cloud G2 came very close to the black hole and will most likely be absorbed by it, observing a unique process provides enormous opportunities for new discoveries of the features of black holes.
(The massive object Sagittarius A*, its mass is 4 million times greater than the Sun, which implies a cluster of stars and the formation of a black hole)
2017. A group of scientists from the multi-country collaboration Event Horizon Telescope, connecting eight telescopes from different points on the Earth’s continents, observed a black hole, which is a supermassive object located in the M87 galaxy, constellation Virgo. The mass of the object is 6.5 billion (!) solar masses, gigantic times larger than the massive object Sagittarius A*, for comparison, with a diameter slightly less than the distance from the Sun to Pluto.
Observations were carried out in several stages, starting in the spring of 2017 and during periods of 2018. The volume of information amounted to petabytes, which then had to be decrypted and a genuine image of an ultra-distant object obtained. Therefore, it took another two whole years to thoroughly process all the data and combine them into one whole.
2019 The data was successfully decrypted and displayed, producing the first ever image of a black hole.
(The first ever image of a black hole in the M87 galaxy in the constellation Virgo)
The image resolution allows you to see the shadow of the point of no return in the center of the object. The image was obtained as a result of ultra-long baseline interferometric observations. These are so-called synchronous observations of one object from several radio telescopes interconnected by a network and located in different parts of the globe, directed in the same direction.
What black holes actually are
A laconic explanation of the phenomenon goes like this.
Everyone knows that there are stars, planets, asteroids and comets in space that can be observed with the naked eye or through a telescope. It is also known that there are special space objects - black holes.A black hole is a space-time region whose gravitational attraction is so strong that no object, including light quanta, can leave it.
The black hole was once a massive star. As long as thermonuclear reactions maintain high pressure in its depths, everything remains normal. But over time, the energy supply is depleted and the celestial body, under the influence of its own gravity, begins to shrink. The final stage of this process is the collapse of the stellar core and the formation of a black hole.
- 1. A black hole ejects a jet at high speed
- 2. A disk of matter grows into a black hole
- 3. Black hole
- 4. Detailed diagram of the black hole region
- 5. Size of new observations found
The most common theory is that similar phenomena exist in every galaxy, including the center of our Milky Way. The huge gravitational force of the hole is capable of holding several galaxies around it, preventing them from moving away from each other. The “coverage area” can be different, it all depends on the mass of the star that turned into a black hole, and can be thousands of light years.
Schwarzschild radius
The main property of a black hole is that any substance that falls into it can never return. The same applies to light. At their core, holes are bodies that completely absorb all light falling on them and do not emit any of their own. Such objects may visually appear as clots of absolute darkness.
- 1. Moving matter at half the speed of light
- 2. Photon ring
- 3. Inner photon ring
- 4. Event horizon in a black hole
Based on Einstein's General Theory of Relativity, if a body approaches a critical distance to the center of the hole, it will no longer be able to return. This distance is called the Schwarzschild radius. What exactly happens inside this radius is not known for certain, but there is the most common theory. It is believed that all the matter of a black hole is concentrated in an infinitesimal point, and at its center there is an object with infinite density, which scientists call a singular disturbance.
How does falling into a black hole happen?
(In the picture, the black hole Sagittarius A* looks like an extremely bright cluster of light)
Not so long ago, in 2011, scientists discovered a gas cloud, giving it the simple name G2, which emits unusual light. This glow may be due to friction in the gas and dust caused by the Sagittarius A* black hole, which orbits it as an accretion disk. Thus, we become observers of the amazing phenomenon of absorption of a gas cloud by a supermassive black hole.
According to recent studies, the closest approach to the black hole will occur in March 2014. We can recreate a picture of how this exciting spectacle will take place.
- 1. When first appearing in the data, a gas cloud resembles a huge ball of gas and dust.
- 2. Now, as of June 2013, the cloud is tens of billions of kilometers from the black hole. It falls into it at a speed of 2500 km/s.
- 3. The cloud is expected to pass by the black hole, but tidal forces caused by the difference in gravity acting on the leading and trailing edges of the cloud will cause it to take on an increasingly elongated shape.
- 4. After the cloud is torn apart, most of it will most likely flow into the accretion disk around Sagittarius A*, generating shock waves in it. The temperature will jump to several million degrees.
- 5. Part of the cloud will fall directly into the black hole. No one knows exactly what will happen to this substance next, but it is expected that as it falls it will emit powerful streams of X-rays and will never be seen again.
Video: black hole swallows a gas cloud
(Computer simulation of how much of the G2 gas cloud would be destroyed and consumed by the black hole Sagittarius A*)
What's inside a black hole
There is a theory that states that a black hole is practically empty inside, and all its mass is concentrated in an incredibly small point located at its very center - the singularity.
According to another theory, which has existed for half a century, everything that falls into a black hole passes into another universe located in the black hole itself. Now this theory is not the main one.
And there is a third, most modern and tenacious theory, according to which everything that falls into a black hole dissolves in the vibrations of strings on its surface, which is designated as the event horizon.
So what is an event horizon? It is impossible to look inside a black hole even with a super-powerful telescope, since even light, entering the giant cosmic funnel, has no chance of emerging back. Everything that can be at least somehow considered is located in its immediate vicinity.
The event horizon is a conventional surface line from under which nothing (neither gas, nor dust, nor stars, nor light) can escape. And this is the very mysterious point of no return in the black holes of the Universe.
A star can turn into a black hole towards the end of its life. During this transformation, the star contracts very strongly, while its mass is maintained. The star turns into a small but very heavy ball. If we assume that our planet Earth will become a black hole, then its diameter in this state will be only 9 millimeters. But the Earth will not be able to turn into a black hole, because completely different reactions take place in the core of planets, not the same as in stars.
Such a strong compression and compaction of the star occurs because, under the influence of thermonuclear reactions in the center of the star, its attractive force increases greatly and begins to attract the surface of the star to its center. Gradually, the speed at which the star contracts increases and eventually begins to exceed the speed of light. When a star reaches this state, it stops glowing because the particles of light - quanta - cannot overcome the force of gravity. A star in this state stops emitting light; it remains “inside” the gravitational radius - the boundary within which all objects are attracted to the surface of the star. Astronomers call this boundary the event horizon. And beyond this boundary, the gravitational force of the black hole decreases. Since light particles cannot overcome the gravitational boundary of a star, a black hole can only be detected using instruments, for example, if for unknown reasons a spaceship or another body - a comet or an asteroid - begins to change its trajectory, it means that it most likely came under the influence of the gravitational forces of a black hole . A controlled space object in such a situation must urgently turn on all engines and leave the zone of dangerous gravity, and if there is not enough power, then it will inevitably be swallowed up by a black hole.
If the Sun could turn into a black hole, then the planets of the solar system would be within the gravitational radius of the Sun and it would attract and absorb them. Fortunately for us, this will not happen, because... Only very large, massive stars can turn into a black hole. The sun is too small for this. During its evolution, the Sun will most likely become an extinct black dwarf. Other black holes that already exist in space are not dangerous for our planet and terrestrial spaceships - they are too far from us.
In the popular TV series "The Big Bang Theory", which you can watch, you will not learn the secrets of the creation of the Universe or the reasons for the emergence of black holes in space. The main characters are passionate about science and work at the physics department at the university. They constantly find themselves in various ridiculous situations, which are fun to watch.
