Gravitational collapse. Gravitational compression Gravitational compression of a star

GRAVITATIONAL COLLAPSE
rapid compression and disintegration of an interstellar cloud or star under the influence of its own gravity. Gravitational collapse is a very important astrophysical phenomenon; it is involved both in the formation of stars, star clusters and galaxies, and in the death of some of them. In interstellar space there are many clouds consisting mainly of hydrogen with a density of approx. 1000 at/cm3, sizes from 10 to 100 St. years. Their structure and, in particular, density continuously change under the influence of mutual collisions, heating by stellar radiation, pressure of magnetic fields, etc. When the density of a cloud or part of it becomes so great that gravity exceeds gas pressure, the cloud begins to shrink uncontrollably - it collapses. Small initial density inhomogeneities become stronger during the collapse process; As a result, the cloud fragments, i.e. breaks up into parts, each of which continues to shrink. Generally speaking, when a gas is compressed, its temperature and pressure increase, which can prevent further compression. But while the cloud is transparent to infrared radiation, it cools easily, and the compression does not stop. However, as the density of individual fragments increases, their cooling becomes more difficult and the increasing pressure stops the collapse - this is how a star is formed, and the entire set of cloud fragments that have turned into stars forms a star cluster. The collapse of a cloud into a star or star cluster lasts about a million years - relatively quickly on a cosmic scale. After this, thermonuclear reactions occurring in the bowels of the star maintain temperature and pressure, which prevents compression. During these reactions, light chemical elements are transformed into heavier ones, releasing enormous energy (similar to what happens when a hydrogen bomb explodes). The released energy leaves the star in the form of radiation. Massive stars emit very intense radiation and burn their “fuel” in just a few tens of millions of years. Low-mass stars have enough fuel to last for many billions of years of slow burning. Sooner or later, any star runs out of fuel, thermonuclear reactions in the core stop and, deprived of a heat source, it remains at the mercy of its own gravity, inexorably leading the star to death.
Collapse of low-mass stars. If, after losing the envelope, the remnant of the star has a mass of less than 1.2 solar, then its gravitational collapse does not go too far: even a shrinking star deprived of heat sources gains a new ability to resist gravity. At a high density of matter, electrons begin to intensively repel each other; this is not due to their electrical charge, but to their quantum mechanical properties. The resulting pressure depends only on the density of the substance and does not depend on its temperature. Physicists call this property of electrons degeneracy. In low-mass stars, the pressure of degenerate matter can resist gravity. The contraction of a star stops when it becomes approximately the size of Earth. Such stars are called white dwarfs because they shine weakly, but immediately after compression they have a rather hot (white) surface. However, the temperature of the white dwarf gradually decreases, and after several billion years such a star is already difficult to notice: it becomes a cold, invisible body.
Collapse of massive stars. If the star's mass is more than 1.2 solar, then the pressure of degenerate electrons is not able to resist gravity, and the star cannot become a white dwarf. Its uncontrollable collapse continues until the substance reaches a density comparable to the density of atomic nuclei (approximately 3*10 14 g/cm3). In this case, most of the matter turns into neutrons, which, like electrons in a white dwarf, become degenerate. The pressure of degenerate neutron matter can stop the contraction of a star if its mass does not exceed approximately 2 solar masses. The resulting neutron star has a diameter of only ca. 20 km. When the rapid contraction of a neutron star suddenly stops, all the kinetic energy turns into heat and the temperature rises to hundreds of billions of kelvins. As a result, a giant flare of the star occurs, its outer layers are thrown out at high speed, and the luminosity increases several billion times. Astronomers call this a "supernova explosion." After about a year, the brightness of the explosion products decreases, the ejected gas gradually cools, mixes with interstellar gas, and in subsequent epochs becomes part of stars of new generations. The neutron star that emerged during the collapse rotates rapidly in the first millions of years and is observed as a variable emitter - a pulsar. If the mass of the collapsing star significantly exceeds 2 solar, then the compression does not stop at the neutron star stage, but continues until its radius decreases to several kilometers. Then the gravitational force on the surface increases so much that even a ray of light cannot leave the star. A star that has collapsed to such an extent is called a black hole. Such an astronomical object can only be studied theoretically, using Einstein's general theory of relativity. Calculations show that the compression of the invisible black hole continues until the matter reaches an infinitely high density.
See also PULSAR; BLACK HOLE.
LITERATURE
Shklovsky I.S., Stars: their birth, life and death. M., 1984

Collier's Encyclopedia. - Open Society. 2000 .

See what "GRAVITATIONAL COLLAPSE" is in other dictionaries:

The process is hydrodynamic. compression of the body under the influence of its own. forces of gravity. This process in nature is possible only in fairly massive bodies, in particular stars. A necessary condition for G.K. a decrease in elasticity in VA inside the star, to a swarm leads to ... ... Physical encyclopedia

Catastrophically fast compression of massive bodies under the influence of gravitational forces. Gravitational collapse can end the evolution of stars with a mass exceeding two solar masses. After the exhaustion of nuclear fuel in such stars, they lose their... ... Encyclopedic Dictionary

Model of the mechanism of gravitational collapse Gravitational collapse is a catastrophically rapid compression of massive bodies under the influence of gravitational forces. Gravitational to... Wikipedia

Catastrophically fast compression of massive bodies under the influence of gravitational forces. Gravitational collapse can end the evolution of stars with a mass exceeding two solar masses. After the exhaustion of nuclear fuel in such stars, they lose their... ... Astronomical Dictionary

Gravitational collapse- (from gravity and lat. collapsus fallen) (in astrophysics, astronomy) catastrophically fast compression of a star in the last stages of evolution under the influence of its own gravitational forces, exceeding the weakening pressure forces of heated gas (matter) ... ... The beginnings of modern natural science

See Gravitational collapse... Great Soviet Encyclopedia

Catastrophically fast compression of massive bodies under the influence of gravity. strength GK may end the evolution of stars with a mass of St. two solar masses. After the exhaustion of nuclear fuel in such stars, they lose their mechanical properties. sustainability and... Natural science. Encyclopedic Dictionary

See Gravitational Collapse... Big Encyclopedic Dictionary

See gravitational collapse. * * * COLLAPSE GRAVITATIONAL COLLAPSE GRAVITATIONAL, see gravitational collapse (see GRAVITATIONAL COLLAPSE) ... Encyclopedic Dictionary

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• Einstein's vision. , Wheeler J.A. , The book by the outstanding American physicist D. A. Wheeler is devoted to an elementary presentation of geometrodynamics - the embodiment of Einstein’s dream “to reduce all physics to geometry.” The author begins with... Category: Mathematics and science Series: Publisher:

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 is gravitational collapse, 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 the end point of the 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 with a large mass to compress very quickly.

Stars weighing more than three solar masses contain enough material for long-lasting thermonuclear reactions. When the substance runs out, the thermonuclear reaction stops, 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.

Such a 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 of a sharp change in the brightness of a 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 of a large amount of 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 the exact value of this parameter. However, it is estimated to be in the range of 2.5 to 3 solar masses. At the 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 a 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 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 them the name quantum black gifts. Their minimum diameter is 10 -18 m, and their 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 the Big Bang, which would make it possible to recreate the process of formation of many space objects, including planet Earth. However, the experiment failed because there was not enough energy to create black holes.

Hydrodynamic compression of an astrophysical object under the influence of its own gravitational forces, leading to a significant reduction in its size

Animation

Description

Gravitational collapse is the hydrodynamic compression of an astrophysical object under the influence of its own gravitational forces, leading to a significant reduction in its size. For the development of gravitational collapse, it is necessary that pressure forces either be absent altogether, or at least be insufficient to counteract the forces of gravity. Gravitational collapse occurs at two extreme stages of stellar evolution. Firstly, the birth of a star begins with the gravitational collapse of the gas and dust cloud from which the star is formed, and, secondly, some stars complete their evolution through gravitational collapse, passing into the final state of a neutron star or black hole.

Gravitational collapse is a consequence of the cessation of thermonuclear reactions in the central region of the star, that is, a consequence of the violation of its thermal and then hydrostatic (mechanical) equilibrium.

The hydrostatic equilibrium equation averaged for the star as a whole has the form:

where m and R are the mass and radius of the star;

r c and p c - density and pressure at the center of the star;

G - gravitational constant;

g is the adiabatic index of the star’s matter.

Analysis of these relationships makes it possible to determine the conditions for the occurrence, continuation or stopping of gravitational collapse. The dependence of the result on the impact has the following form:

,

where V is the fall velocity (radial non-relativistic case);

r g - gravitational radius of the object;

r is the distance to the layer (to the particle);

E is the total energy of the particle;

m - particle mass;

c is the speed of light.

For angular velocities the following relation is valid:

,

where w 0 and R0 are the initial angular velocity and radius of the object;

w 1 and R 1 - final (current) angular velocity and radius.

For g > 4/3, where g is the adiabatic exponent of the star's matter, hydrostatic equilibrium is stable and collapse does not occur. In this case, we are talking about the average value of the indicator. A rigorous theory of hydrostatic stability of stars must take into account the difference in g for different layers of the star.

A star can have a spherical or parabolic shape (Fig. 1, 2).

Collapse of a spherical star

Rice. 1

Collapse of a gravitating mass in the shape of a disk

Rice. 2

Its own gravitational field acts on the entire space around the gravitating center. The movement of matter is directed towards the gravitating center. The gravitating region of space is determined by Rayleigh instability or a certain limiting concentration of matter. The gravitational field is directed towards the gravitating center. The pressure exists in the gravitating region of the star's space and is not the same for different layers of the star's matter.

The result of this effect can be used in chronometry. Optical effects caused by superdense objects can be used in astronomy.

A pulsar is a compact rotating object with a very strong magnetic field - the result of gravitational collapse. Under certain conditions, it can have a very slowly varying orbital period. Such a pulsar can be successfully used as a time and frequency standard.

Theoretically possible application: particle separation in the ergosphere of a rotating black hole (a possible result of gravitational collapse). The fall of a part into a black hole leads to a slingshot effect - the ejection of the remaining part into the surrounding space with very high energy. This is how gravitational accelerators of the future could work. Their most important feature and advantage is the ability to accelerate any particles, regardless of their electric, leptonic, baryon charges, spin, magnetic moment, etc.

Timing characteristics

Initiation time (log to 7 to 9);

Lifetime (log tc from 13 to 15);

Degradation time (log td from 14 to 16);

Time of optimal development (log tk from 10 to 12).

Diagram:

Technical implementations of the effect

technical implementation of the effect

There are known astronomical objects - pulsars - compact rotating objects with a very strong magnetic field, resulting from gravitational collapse. Under certain conditions they have a very slowly changing period of revolution. One of these pulsars can be successfully used as a time and frequency standard, available for use anywhere in the world.

Applying an effect

Theoretically possible way of application: gravitational collapse - a universal particle accelerator capable of accelerating any particles, regardless of their electric, leptonic, baryon charges, spin, magnetic moment, etc.

The rapid process of compression of matter under the influence of its own attraction is called (see Gravity). Sometimes gravitational collapse is understood as the unlimited compression of matter into a black hole, described by the general theory of relativity (relativistic collapse).

Parts of any body experience mutual gravitational attraction. However, in most bodies its magnitude is insufficient to cause collapse. For a given mass of a body, the greater the internal field of gravitational extension, the greater its density, i.e. the smaller its size. In order for the gravitational field to become noticeable, it is necessary to compress it to colossal densities. So, for example, in order for the gravitational collapse of the Earth to occur, its density must increase to 10 27 g/cm 3, i.e. trillions of times higher than nuclear density. However, as the mass increases, the internal field of gravitational attraction also increases and the density value sufficient for collapse decreases.

In such massive objects as stars, the role of gravitational compression forces becomes decisive. These same forces cause compression of gas clouds during the formation of stars and galaxies. Such compression has the character of a peculiar fall of gas particles towards the center of the forming star or galaxy. In this sense, they talk about the gravitational collapse of protostars and protogalaxies.

The existence of stars is associated with the mutual attraction of their atoms, but in ordinary stars this attraction is balanced by the internal pressure of matter, which ensures their stability. At high temperatures and densities characteristic of the interior of stars, atoms of matter are ionized and the pressure of matter is determined by the movement of free electrons and ions. At the main, longest stages of stellar evolution, such motion is thermal. It is supported by the release of energy during thermonuclear fusion reactions (see Stars). However, the supply of thermonuclear fuel in stars is limited and the final fate of stars is determined by the possibility of balancing the forces of gravitational compression and the pressure of the cooling substance of a star that has exhausted its entire supply of thermal energy. Such equilibrium conditions are realized in a white dwarf or in the degenerate cores of stars with a mass less than 5-10 solar masses, where gravitational compression is counteracted by electron pressure. But in a white dwarf or degenerate core of a star with a higher mass, the density of electrons becomes so high that they seem to be pressed into the core and, interacting with nuclear matter, turn into neutrinos. This capture of electrons by nuclei leads to a decrease in the electron pressure counteracting gravitational compression, and gravitational collapse occurs.

Gravitational collapse in a white dwarf or degenerate stellar core is accompanied by further capture of electrons by the nuclei and intense neutrino radiation, which carries away almost all the energy of gravitational compression. The electron pressure becomes less and less, so the compression represents a free fall of matter towards the center of the star. Ultimately, the collapsing substance consists of only neutrons. The resulting pressure of neutron matter can balance the forces of gravitational compression, and the gravitational collapse will end with the formation of a neutron star. Neutrino radiation during collapse into a neutron star can provide effective energy transfer to the outer layers of the collapsing star, sufficient for their release with high kinetic energy; In this case, a supernova explosion is observed.

However, the gravitational collapse of massive stars with masses exceeding 5-10 solar masses does not end at the neutron star stage. As the mass of a neutron star increases, the density of its matter increases and the repulsion of neutrons can no longer provide effective resistance to gravitational compression. The collapse turns into relativistic gravitational collapse, and a black hole is formed. The presence of the maximum mass of a stable white dwarf and a neutron star means that massive stars (with a mass 10 times the mass of the Sun) will inevitably end their existence in a process of relativistic gravitational collapse.

Gravitational collapse into a black hole is a phenomenon in which the effects of general relativity become dominant. The collapse itself occurs as a free fall towards the center of the resulting black hole, but in accordance with the laws of general relativity, a distant observer will see this fall as if in increasingly slow motion filming: for him, the collapse process will continue indefinitely. When collapsing into a black hole, the geometric properties of space and time change. The bending of light rays turns out to be so strong that no signal can leave the surface of the collapsing body. The matter that has gone under the radius of the black hole is completely isolated from the rest of the world, however, continuing to influence the environment with its gravitational field.

rapid compression and disintegration of an interstellar cloud or star under the influence of its own gravity. Gravitational collapse is a very important astrophysical phenomenon; it is involved both in the formation of stars, star clusters and galaxies, and in the death of some of them. In interstellar space there are many clouds consisting mainly of hydrogen with a density of approx. 1000 at/cm3, sizes from 10 to 100 St. years. Their structure, in particular, density continuously changes under the influence of mutual collisions, heating by stellar radiation, pressure of magnetic fields, etc. When the density of a cloud or part of it becomes so great that gravity exceeds gas pressure, the cloud begins to shrink uncontrollably - it collapses. Small initial density inhomogeneities become stronger during the collapse process; As a result, the cloud fragments, i.e. breaks up into parts, each of which continues to shrink. Generally speaking, when a gas is compressed, its temperature and pressure increase, which can prevent further compression. But while the cloud is transparent to infrared radiation, it cools easily, and the compression does not stop. However, as the density of individual fragments increases, their cooling becomes more difficult and the increasing pressure stops the collapse - this is how a star is formed, and the entire set of cloud fragments that have turned into stars forms a star cluster. The collapse of a cloud into a star or star cluster lasts about a million years - relatively quickly on a cosmic scale. After this, thermonuclear reactions occurring in the bowels of the star maintain temperature and pressure, which prevents compression. During these reactions, light chemical elements are transformed into heavier ones, releasing enormous energy (similar to what happens when a hydrogen bomb explodes). The released energy leaves the star in the form of radiation. Massive stars emit very intense radiation and burn their “fuel” in just a few tens of millions of years. Low-mass stars have enough fuel to last for many billions of years of slow burning. Sooner or later, any star runs out of fuel, thermonuclear reactions in the core stop and, deprived of a heat source, it remains at the mercy of its own gravity, inexorably leading the star to death. Collapse of low-mass stars. If, after losing the envelope, the remnant of the star has a mass of less than 1.2 solar, then its gravitational collapse does not go too far: even a shrinking star deprived of heat sources gains a new ability to resist gravity. At a high density of matter, electrons begin to intensively repel each other; this is not due to their electrical charge, but to their quantum mechanical properties. The resulting pressure depends only on the density of the substance and does not depend on its temperature. Physicists call this property of electrons degeneracy. In low-mass stars, the pressure of degenerate matter can resist gravity. The contraction of a star stops when it becomes approximately the size of Earth. Such stars are called white dwarfs because they shine weakly, but immediately after compression they have a rather hot (white) surface. However, the temperature of the white dwarf gradually decreases, and after several billion years such a star is already difficult to notice: it becomes a cold, invisible body. Collapse of massive stars. If the star's mass is more than 1.2 solar, then the pressure of degenerate electrons is not able to resist gravity, and the star cannot become a white dwarf. Its uncontrollable collapse continues until the substance reaches a density comparable to the density of atomic nuclei (approximately 3? 1014 g/cm3). In this case, most of the matter turns into neutrons, which, like electrons in a white dwarf, become degenerate. The pressure of degenerate neutron matter can stop the contraction of a star if its mass does not exceed approximately 2 solar masses. The resulting neutron star has a diameter of only ca. 20 km. When the rapid contraction of a neutron star suddenly stops, all the kinetic energy turns into heat and the temperature rises to hundreds of billions of kelvins. As a result, a giant flare of the star occurs, its outer layers are thrown out at high speed, and the luminosity increases several billion times. Astronomers call this a "supernova explosion." After about a year, the brightness of the explosion products decreases, the ejected gas gradually cools, mixes with interstellar gas, and in subsequent epochs becomes part of stars of new generations. The neutron star that emerged during the collapse rotates rapidly in the first millions of years and is observed as a variable emitter - a pulsar. If the mass of the collapsing star significantly exceeds 2 solar, then the compression does not stop at the neutron star stage, but continues until its radius decreases to several kilometers. Then the gravitational force on the surface increases so much that even a ray of light cannot leave the star. A star that has collapsed to such an extent is called a black hole. Such an astronomical object can only be studied theoretically, using Einstein's general theory of relativity. Calculations show that the compression of the invisible black hole continues until the matter reaches an infinitely high density. See also PULSAR; BLACK HOLE.