What's happened black hole? Why is it called black? What happens in the stars? How are a neutron star and a black hole related? Is the Large Hadron Collider capable of creating black holes, and what does this mean for us?
What's happened star??? If you don’t know yet, our Sun is also a star. This is an object large sizes capable of emitting electromagnetic waves using thermonuclear fusion (this is not the most accurate of definitions). If it’s not clear, we can say this: a star is large object spherical shape, inside of which, using nuclear reactions A very, very, very large amount of energy is generated, part of which is used to emit visible light. In addition to ordinary light, heat is also emitted ( infrared radiation), and radio waves, and ultraviolet, etc.
Nuclear reactions occur in any star in the same way as in nuclear power plants, with only two main differences.
1. Nuclear fusion reactions occur in stars, that is, the combination of nuclei, and in nuclear power plants – nuclear decay. In the first case, 3 times more energy is released, thousands of times less cost, since only hydrogen is needed, and it is relatively inexpensive. Also, in the first case there is no harmful waste: only harmless helium is released. Now, of course, you are wondering why such reactions are not used at nuclear power plants? Because it is UNCONTROLLED and easily leads to nuclear explosion, and this reaction requires a temperature of several million degrees. For man nuclear fusion is the most important and most difficult task (no one has yet figured out a way to control thermonuclear fusion), given that our energy sources are running out.
2. In stars, more matter is involved in reactions than in nuclear power plants, and, naturally, there is more energy output there.
Now about the evolution of stars. Every star is born, grows, ages and dies (extinguishes). Based on their evolutionary style, stars are divided into three categories depending on their mass.
First category – stars with a mass less than 1.4 * The mass of the Sun. In such stars, all the “fuel” slowly turns into metal, because due to the fusion (combination) of nuclei, more and more “multinuclear” (heavy) elements appear, and these are metals. True, the last stage of the evolution of such stars has not been recorded (it is difficult to detect metal balls), this is just a theory.
Second category –
stars in mass exceeding the mass of stars of the first category, but less than three solar masses. Such stars lose their balance as a result of evolution internal forces attraction and repulsion. As a result, their outer shell is thrown into space, and the inner shell (from the law of conservation of momentum) begins to “furiously” shrink. A neutron star is formed. It consists almost entirely of neutrons, that is, of particles that do not have electric charge. The most remarkable thing about a neutron star –
this is its density, because to become neutron, a star needs to be compressed into a ball with a diameter of only about 300 km, and this is very small. So its density is very high - about tens of trillions of kg in one cubic meter, which is billions of times greater than the density of the densest substances on Earth. Where did this density come from? The fact is that all substances on Earth consist of atoms, which in turn consist of nuclei. Each atom can be imagined as a large empty ball (absolutely empty), in the center of which there is a small nucleus. The nucleus contains the entire mass of the atom (besides the nucleus, the atom contains only electrons, but their mass is very small). The diameter of the nucleus is 1000 times smaller than an atom. This means that the volume of the nucleus is 1000*1000*1000 = 1 billion times smaller than an atom. And hence the core density is billions of times more density atom. What happens in a neutron star? Atoms cease to exist as a form of matter; they are replaced by nuclei. That is why the density of such stars is billions of times greater than the density of terrestrial substances.
We all know that heavy objects (planets, stars) strongly attract everything around them. Neutron stars are discovered that way. They greatly distort the orbits of others visible stars, located nearby.
Third category of stars – stars with a mass greater than three times the mass of the Sun. Such stars, having become neutron, compress further and turn into black holes. Their density is tens of thousands of times greater than the density of neutron stars. Having such a huge density, a black hole gains the ability to strong gravity(the ability to attract surrounding bodies). With such gravity, the star does not allow you to leave its limits even electromagnetic waves, and therefore the light. That is, a black hole does not emit light. Lack of any light – it's darkness, that's why black hole and is called black. It is always black and cannot be seen with any telescope. Everyone knows that due to their gravity, black holes are capable of sucking in all surrounding bodies into themselves. large volume. That is why people are wary of launching the Large Hadron Collider, in the work of which, according to scientists, the appearance of black microholes is possible. However, these microholes are very different from ordinary ones: they are unstable because their lifetime is very short, and have not been practically proven. Moreover, scientists claim that these microholes have a completely different nature compared to ordinary black holes and are not capable of absorbing matter.
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This post is a summary for the fifth lesson in the astrophysics course program for high school. It contains a description of supernova explosions, processes of formation of neutron stars (pulsars) and stellar-mass black holes, both single and in stellar pairs. And a few words about brown dwarfs.
First, I will repeat the picture showing the classification of types of stars and their evolution depending on their masses:
1. Outbursts of novae and supernovae.
The burning of helium in the depths of stars ends with the formation of red giants and their outbursts as new with education white dwarfs or the formation of red supergiants and their outbursts as supernovae with education neutron stars or black holes, as well as nebulae from the shells ejected by these stars. Often the masses of the ejected shells exceed the masses of the “mummies” of these stars - neutron stars and black holes. To understand the scale of this phenomenon, I will provide a video of the supernova 2015F explosion at a distance of 50 million light years from us. years of galaxy NGC 2442:
Another example is the supernova of 1054 in our Galaxy, as a result of which the Crab Nebula and a neutron star were formed at a distance of 6.5 thousand light years from us. years. In this case, the mass of the resulting neutron star is ~ 2 solar masses, and the mass of the ejected shell is ~ 5 solar masses. Contemporaries estimated the brightness of this supernova to be about 4-5 times greater than that of Venus. If such a supernova flared up a thousand times closer (6.5 light years), then it would sparkle 4000 times more in our sky brighter than the moon, but a hundred times weaker than the Sun.
2. Neutron stars.
Stars large masses(classes O, B, A) after hydrogen burns out into helium and during the process of helium burnout predominantly into carbon, oxygen and nitrogen enter a fairly short stage red supergiant and upon completion of the helium-carbon cycle, they also shed the shell and flare up as "Supernovae". Their depths are also compressed under the influence of gravity. But the pressure of the degenerate electron gas can no longer, like in white dwarfs, stop this gravitational self-compression. Therefore, the temperature in the bowels of these stars rises and thermonuclear reactions begin to occur in them, as a result of which the following elements Periodic tables. Up to gland.
Why before iron? Because the formation of nuclei with large atomic number does not occur with the release of energy, but with its absorption. But taking it from other nuclei is not so easy. Of course, elements with high atomic numbers are formed in the depths of these stars. But in much smaller quantities than iron.
But then evolution splits. Not too massive stars (classes A and partially IN) turn into neutron stars . In which electrons are literally imprinted into protons and most of the star's body turns into a huge one neutron nucleus. Consisting of ordinary neutrons touching and even pressed into each other. The density of the substance in which is on the order of several billion tons per cubic centimeter. A typical neutron star diameter- about 10-20 kilometers. A neutron star is the second stable type of "mummy" of a dead star. Their masses typically range from about 1.3 to 2.1 solar masses (according to observational data).
Single neutron stars are almost impossible to see optically due to their extremely low luminosity. But some of them find themselves as pulsars. What it is? Almost all stars rotate around their axis and have a fairly strong magnetic field. For example, our Sun rotates around its axis in about a month.
Now imagine that its diameter will decrease a hundred thousand times. It is clear that, thanks to the law of conservation of angular momentum, it will rotate much faster. And the magnetic field of such a star near its surface will be many orders of magnitude stronger than the solar one. Most neutron stars have a rotation period around their axis of tenths to hundredths of a second. From observations it is known that the fastest rotating pulsar makes just over 700 revolutions around its axis per second, and the slowest rotating one makes one revolution in more than 23 seconds.
Now imagine that such a star’s magnetic axis, like the Earth’s, does not coincide with the axis of rotation. Hard radiation from such a star will be concentrated in narrow cones along the magnetic axis. And if this cone “touches” the Earth with the rotation period of the star, then we will see this star as a pulsating source of radiation. Like a flashlight rotated by our hand.
Such a pulsar (neutron star) was formed after a supernova explosion in 1054, which occurred just during the visit of Cardinal Humbert to Constantinople. As a result of which there was a final break between the Catholic and Orthodox churches. This pulsar itself makes 30 revolutions per second. And the shell it ejected with a mass of ~ 5 solar masses looks like Crab Nebula:
3. Black holes (stellar masses).
Finally, fairly massive stars (classes ABOUT and partially IN) finish their life path the third type of "mummy" - black hole. Such an object arises when the mass of a stellar remnant is so large that the pressure of contacting neutrons (the pressure of a degenerate neutron gas) in the depths of this remnant cannot resist its gravitational self-compression. Observations show that the mass boundary between neutron stars and black holes lies in the vicinity of ~2.1 solar masses.
It is impossible to observe a single black hole directly. For no particle can escape from its surface (if it exists). Even a particle of light is a photon.
4. Neutron stars and black holes in binaries star systems.
Single neutron stars and stellar-mass black holes are practically unobservable. But in cases where they are one of two or more stars in close star systems, such observations become possible. Since with their gravity they can “suck out” the outer shells of the remaining normal stars their neighbors.
With this "suction" around a neutron star or black hole, a accretion disk, the matter of which partially “slides” towards a neutron star or black hole and is partially thrown away from it in two jets. This process can be recorded. An example is the binary star system in SS433, one component of which is either a neutron star or a black hole. And the second one is still an ordinary star:
5. Brown dwarfs.
Stars with masses noticeably less than the solar mass and up to ~0.08 solar masses are class M red dwarfs. They will operate on the hydrogen-helium cycle for a time greater than the age of the Universe. In objects with masses less than this limit, for a number of reasons, a stationary long-running thermonuclear fusion is not possible. Such stars are called brown dwarfs. Their surface temperature is so low that they are almost invisible in optics. But they shine in the infrared range. For the combination of these reasons, they are often called substars.
The mass range of brown dwarfs is from 0.012 to 0.08 solar masses. Objects with a mass less than 0.012 solar masses (~12 Jupiter masses) can only be planets. Gas giants. Due to slow gravitational self-compression, they radiate noticeably more energy than they receive from their parent stars. Thus, Jupiter, based on the sum of all ranges, emits approximately twice as much energy as it receives from the Sun.
White dwarfs, neutron stars and black holes are various shapes the final stage of stellar evolution. Young stars derive their energy from thermonuclear reactions occurring in the stellar interior; During these reactions, hydrogen is converted into helium. After a certain proportion of hydrogen is consumed, the resulting helium core begins to shrink. Further evolution of a star depends on its mass, or more precisely on how it relates to a certain critical value called the Chandrasekhar limit. If the mass of the star is less than this value, then the pressure of the degenerate electron gas stops the compression (collapse) of the helium core before its temperature reaches such a value. high value when thermonuclear reactions begin, during which helium is converted into carbon. Meanwhile, the outer layers of the evolving star are shed relatively quickly. (It is assumed that this is how they are formed planetary nebulae.) White dwarf and is a helium core surrounded by a more or less extended hydrogen shell.
Have more massive stars the helium core continues to contract until the helium “burns out.” The energy released as helium turns into carbon prevents the core from collapsing further - but not for long. After the helium is completely consumed, the compression of the core continues. The temperature rises again, other nuclear reactions begin, which proceed until the energy stored in the atomic nuclei is exhausted. At this point, the star’s core already consists of pure iron, which plays the role of nuclear “ash.” Now nothing can prevent the further collapse of the star - it continues until the density of its matter reaches the density of atomic nuclei. The sharp compression of matter in the central regions of the star generates an explosion of enormous force, as a result of which the outer layers of the star fly apart at enormous speeds. It is these explosions that astronomers associate with the phenomenon of supernovae.
The fate of a collapsing stellar remnant depends on its mass. If the mass is less than approximately 2.5M 0 (the mass of the Sun), then the pressure due to the “zero” motion of neutrons and protons is large enough to prevent further gravitational compression of the star. Objects in which the density of matter is equal to (or even exceeds) the density of atomic nuclei are called neutron stars. Their properties were first studied in the 30s by R. Oppenheimer and G. Volkov.
According to Newton's theory, the radius of a collapsing star decreases to zero in a finite time, gravitational potential at the same time increases indefinitely. Einstein's theory paints a different scenario. The photon's speed decreases as it approaches the center of the black hole, becoming equal to zero. This means that from the point of view of an external observer, a photon falling into a black hole will never reach its center. Since particles of matter cannot move faster than a photon, the radius of a black hole will reach its limit value in an infinite time. Moreover, photons emitted from the surface of the black hole experience an increasing redshift throughout the collapse. From the point of view of an external observer, the object from which the black hole is formed initially contracts at an ever-increasing rate; then its radius begins to decrease more and more slowly.
Not having internal sources energy, neutron stars and black holes cool quickly. And since their surface area is very small - only a few tens square kilometers, - one should expect that the brightness of these objects is extremely low. Really, thermal radiation The surfaces of neutron stars or black holes have not yet been observed. However, some neutron stars are powerful sources non-thermal radiation. It's about about the so-called pulsars discovered in 1967 by Jocelyn Bell - graduate student Cambridge University. Bell studied radio signals recorded using equipment developed by Anthony Hewish to study the radiation of oscillating radio sources. Among the many recordings of chaotically flickering sources, she noticed one where the bursts were repeated with a clear periodicity, although they varied in intensity. More detailed observations confirmed the precisely periodic nature of the pulses, and when studying other records, two more sources with the same properties were discovered. Observations and theoretical analysis show that pulsars are rapidly rotating neutron stars with unusually strong magnetic fields. The pulsating nature of the radiation is caused by a beam of rays emerging from “hot spots” on (or near) the surface of a rotating neutron star. The detailed mechanism of this radiation still remains a mystery to scientists.
Several neutron stars have been discovered that are part of close dual systems. It is these (and no other) neutron stars that are powerful sources x-ray radiation. Let's imagine a close binary, one component of which is a giant or supergiant, and the other is a compact star. Under the influence gravitational field of a compact star, gas can flow out of the rarefied atmosphere of the giant: such gas flows in close binary systems, discovered long ago by methods spectral analysis, received an appropriate theoretical interpretation. If the compact star in a binary system is a neutron star or black hole, then gas molecules escaping from another component of the system can be accelerated to very high speeds. high energies. Due to collisions between molecules kinetic energy gas falling onto a compact star eventually turns into heat and radiation. As estimates show, the energy released in this case fully explains the observed intensity of X-ray emission from binary systems of this type.
In Einstein's general theory of relativity, black holes occupy the same place as ultrarelativistic particles in his special theory relativity. But if the world of ultrarelativistic particles - high energy physics - is full amazing phenomena who play important role V experimental physics and observational astronomy, the phenomena associated with black holes still cause only surprise. Black hole physics will eventually yield results that are important for cosmology, but for now this branch of science is largely a playground for theorists. Doesn't it follow from this that Einstein's theory of gravity gives us less information about the Universe than Newton's theory, although in theoretically significantly superior to it? Not at all! Unlike Newton's theory, Einstein's theory forms the foundation of a self-consistent model real universe as a whole, that this theory has many striking and testable predictions and, finally, it provides causation between freely falling, non-rotating frames of reference and distribution, as well as the movement of mass in outer space.
A black hole is a neutron star, or more precisely, a black hole is one of the varieties of neutron stars.
A black hole, like a neutron star, consists of neutrons. Moreover, this is not a neutron gas, in which neutrons are in a free state, but a very dense substance with the density of an atomic nucleus.
Black holes and neutron stars form as a result of gravitational collapse, when the gas pressure in the star cannot balance its gravitational compression. At the same time, the star contracts to a very small size and very high density, so that electrons are pressed into protons and neutrons are formed.
Note that the average lifetime of a free neutron is about 15 minutes (half-life is about 10 minutes). Therefore, neutrons in neutron stars and black holes can only be in bound state, as in atomic nuclei. Therefore, a neutron star and a black hole are like an atomic nucleus of macroscopic size, in which there are no protons.
The absence of protons is one difference between a black hole and a neutron star from an atomic nucleus. The second difference is due to the fact that in ordinary atomic nuclei neutrons and protons are “glued” to each other using nuclear forces (the so-called “strong” interaction). And in neutron stars, neutrons are “glued together” by gravity.
The fact is that nuclear forces also need protons to “glue” neutrons together. There are no nuclei that consist only of neutrons. There must be at least one proton. And for gravity, no protons are needed to “glue” neutrons together.
Another difference between gravity and nuclear forces is that gravity is a long-range interaction, and nuclear forces are a short-range interaction. That's why atomic nuclei cannot be macroscopic in size. Starting with uranium, all elements periodic table Mendeleev have unstable nuclei that decay due to the fact that positively charged protons repel each other and break apart large nuclei.
Neutron stars and black holes do not have this problem, because, firstly, gravitational forces long-range, and, secondly, there are no positively charged protons in neutron stars and black holes.
A neutron star and a black hole under the influence of gravitational forces have the shape of a ball, or rather an ellipsoid of rotation, since all neutron stars (and black holes) rotate around their axis. And quite quickly, with rotation periods of several seconds or less.
The fact is that neutron stars and black holes are formed from ordinary stars by their strong compression under the influence of gravity. Therefore, according to the law of conservation of torque, they must rotate very quickly.
Are the surfaces of black holes and neutron stars solid? Not in the sense solid, as an aggregate states of matter, but in the sense of a clear surface of the ball, without a neutron atmosphere. Apparently, yes, black holes and neutron stars have a solid surface. The neutron atmosphere and neutron liquid are neutrons in a free state, which means they must decay.
But this does not mean that if we, for example, drop some “product” made of neutrons with the density of an atomic nucleus onto the surface of a black hole or a neutron star, then it will remain on the surface of the star. Such a hypothetical “product” will immediately be “sucked” into the interior of a neutron star and a black hole.
The difference between black holes and neutron stars
The gravity of a black hole is such that the escape velocity on its surface exceeds the speed of light. Therefore, light from the surface of a black hole cannot forever go into open space. Gravitational forces bend the light beam back.
If there is a light source on the surface of a black hole, then the photons of this light first fly upward, and then turn and fall back to the surface of the black hole. Or these photons begin to rotate around the black hole in an elliptical orbit. The latter occurs on a black hole on the surface of which the first escape velocity is less than the speed of light. In this case, the photon can escape from the surface of the black hole, but it becomes a permanent companion of the black hole.
And on the surface of all other neutron stars that are not black holes, the second escape velocity is less than the speed of light. Therefore, if on the surface there is such neutron hole there is a light source, then photons from this light source leave the surface of such a neutron star in hyperbolic orbits.
It is clear that all these considerations apply not only to visible light, but also to any electromagnetic radiation. That is, not only cannot leave a black hole visible light, but also radio waves, infrared rays, ultraviolet, x-ray and gamma radiation. The maximum that photons of these radiations and waves can do is begin to rotate around a black hole, if for a given black hole the speed of light is greater than the first escape velocity on the surface of the star.
That is why such neutron stars are called “black holes”. Nothing flies out of a black hole, but anything can fly in. (Evaporation of black holes due to quantum tunneling We will not consider it here.)
That is, it is clear that there is actually no hole in space there. Just like there is no hole in space at the location of an ordinary neutron star or at the location of an ordinary star.
Holes in space exist only in books by science fiction writers, popular science publications and television programs. Publications and television programs need to financially recoup the costs of circulation and ratings. Therefore, they have to emotionally amaze their readers and television viewers with facts that cannot be verified at the current level of development of science and technology, but which may appear in some mathematical models. (The lay public is usually unaware that mathematical models in physics it is always secondary that physics is an experimental science and that mathematical models of physical objects tend to change in the future as new experimental data become available.)
If we could stand on the surface of a black hole, then looking up we would see a translucent mirror instead of a starry sky. That is, we would see there both the surrounding space (since the black hole receives all the radiation sent to it) and the light that returns to us without being able to overcome gravity. This return of light back has a mirror effect.
Exactly the same translucent “mirror” on the surface of a black hole occurs for other types of electromagnetic radiation (radio waves, X-rays, ultraviolet, etc.)
Many amazing things happen in space, as a result of which new stars appear, old ones disappear and black holes form. One of the magnificent and mysterious phenomena gravitational collapse occurs, which ends the evolution of stars.
Stellar evolution is the cycle of changes a star goes through over its lifetime (millions or billions of years). When the hydrogen in it runs out and turns into helium, a helium core is formed, and it itself begins to turn into a red giant - a star of late spectral classes that has high luminosity. Their mass can be 70 times the mass of the Sun. Very bright supergiants are called hypergiants. In addition to high brightness, they are characterized by a short lifetime.
The essence of collapse
This phenomenon is considered end point evolution of stars whose weight is more than three solar masses (the weight of the Sun). This quantity is used in astronomy and physics to determine the weight of other cosmic bodies. Collapse occurs when gravitational forces cause huge cosmic bodies to collapse large mass shrink very quickly.
Stars weighing more than three solar masses contain enough material for long-lasting thermonuclear reactions. When the substance runs out, it stops and thermonuclear reaction, and the stars cease to be mechanically stable. This leads to the fact that they begin to compress towards the center at supersonic speed.
Neutron stars
When stars contract, this creates internal pressure. If it grows with sufficient force to stop the gravitational compression, then a neutron star appears.
This cosmic body has a simple structure. A star consists of a core, which is covered by a crust, and this, in turn, is formed from electrons and atomic nuclei. It is approximately 1 km thick and is relatively thin compared to other bodies found in space.
The weight of neutron stars is equal to the weight of the Sun. The difference between them is that their radius is small - no more than 20 km. Inside them, atomic nuclei interact with each other, thus forming nuclear matter. It is the pressure from its side that prevents the neutron star from contracting further. This type of star has a very high rotation speed. They are capable of making hundreds of revolutions within one second. The birth process begins from a supernova explosion, which occurs during the gravitational collapse of a star.
Supernovae
A supernova explosion is a phenomenon sudden change brightness of the star. Then the star begins to slowly and gradually fade. This is how the last stage of gravitational collapse ends. The entire cataclysm is accompanied by the release large quantity energy.
It should be noted that the inhabitants of the Earth can see this phenomenon only after the fact. The light reaches our planet long after the outbreak occurs. This has caused difficulties in determining the nature of supernovae.
Neutron star cooling
After the end of the gravitational contraction that resulted in the formation of a neutron star, its temperature is very high (much higher than the temperature of the Sun). The star cools down due to neutrino cooling.
Within a couple of minutes, their temperature can drop 100 times. Over the next hundred years - another 10 times. After it decreases, the cooling process slows down significantly.
Oppenheimer-Volkoff limit
On the one hand, this indicator reflects the maximum possible weight of a neutron star at which gravity is compensated by neutron gas. This prevents gravitational collapse from ending in a black hole. On the other hand, the so-called Oppenheimer-Volkoff limit is also a lower threshold for the weight of a black hole that was formed during stellar evolution.
Due to a number of inaccuracies it is difficult to determine exact value this parameter. However, it is estimated to be in the range of 2.5 to 3 solar masses. On this moment, scientists say that the heaviest neutron star is J0348+0432. Its weight is more than two solar masses. The lightest black hole weighs 5-10 solar masses. Astrophysicists say that these data are experimental and relate only to currently known neutron stars and black holes and suggest the possibility of the existence of more massive ones.
Black holes
A black hole is one of the most amazing phenomena found in space. It represents the region of space-time where gravitational attraction does not allow any objects to escape from it. Even bodies that can move at the speed of light (including quanta of light itself) are unable to leave it. Before 1967, black holes were called "frozen stars", "collapsars" and "collapsed stars".
A black hole has its opposite. It's called a white hole. As you know, it is impossible to get out of a black hole. As for the whites, they cannot be penetrated.
In addition to gravitational collapse, the formation of a black hole can be caused by a collapse at the center of the galaxy or the protogalactic eye. There is also a theory that black holes appeared as a result of the Big Bang, just like our planet. Scientists call them primary.
There is one black hole in our Galaxy, which, according to astrophysicists, was formed due to the gravitational collapse of supermassive objects. Scientists say that such holes form the cores of many galaxies.
Astronomers in the United States suggest that the size of large black holes may be significantly underestimated. Their assumptions are based on the fact that for the stars to reach the speed with which they move through the M87 galaxy, located 50 million light years from our planet, the mass of the black hole in the center of the M87 galaxy must be at least 6.5 billion solar masses. At the moment, it is generally accepted that the weight of the largest black hole is 3 billion solar masses, that is, more than half as much.
Black hole synthesis
There is a theory that these objects may appear as a result of nuclear reactions. Scientists have given They are called quantum black gifts. Their minimum diameter is 10 -18 m, and the smallest mass is 10 -5 g.
The Large Hadron Collider was built to synthesize microscopic black holes. It was assumed that with its help it would be possible not only to synthesize a black hole, but also to simulate Big Bang, which would make it possible to recreate the process of formation of a set space objects, including planet Earth. However, the experiment failed because there was not enough energy to create black holes.