The hypothesis of the existence of neutron stars was put forward by astronomers W. Baade and F. Zwicky immediately after the discovery of the neutron in 1932. But this hypothesis was confirmed by observations only after the discovery of pulsars in 1967.

Neutron stars are formed as a result of the gravitational collapse of normal stars with masses several times that of the sun. The density of a neutron star is close to the density atomic nucleus, i.e. 100 million times higher than the density of ordinary matter. Therefore, with its huge mass, a neutron star has a radius of only approx. 10 km.

Due to the small radius of a neutron star, the force of gravity on its surface is extremely high: about 100 billion times higher than on Earth. This star is kept from collapse by the “degeneracy pressure” of dense neutron matter, which does not depend on its temperature. However, if the mass of the neutron star becomes greater than about 2 solar masses, then gravity will exceed this pressure and the star will not be able to withstand the collapse.

Neutron stars have a very strong magnetic field, reaching 10 12 -10 13 gauss on the surface (for comparison: the Earth has about 1 gauss). Associated with neutron stars celestial objects two different types.

Pulsars

(radio pulsars). These objects strictly regularly emit pulses of radio waves. The radiation mechanism is not completely clear, but it is believed that a rotating neutron star emits a radio beam in the direction associated with its magnetic field, the symmetry axis of which does not coincide with the axis of rotation of the star. Therefore, the rotation causes the rotation of the radio beam periodically sent to the Earth.

X-ray doubles.

Pulsating X-ray sources are also associated with neutron stars that are part of a binary system with a massive normal star. In such systems, gas from the surface of a normal star falls onto a neutron star, accelerating up to great speed. When hitting the surface of a neutron star, the gas releases 10–30% of its rest energy, while when nuclear reactions this figure does not even reach 1%. The surface of a neutron star heated to a high temperature becomes a source x-ray radiation. However, the fall of gas does not occur uniformly over the entire surface: the strong magnetic field of a neutron star captures the incident ionized gas and directs it towards magnetic poles, where he falls, as in a funnel. Therefore, only the regions of the poles become strongly heated, which on a rotating star become sources of X-ray pulses. Radio pulses from such a star no longer arrive, since radio waves are absorbed in the gas surrounding it.

Compound.

The density of a neutron star increases with depth. Under a layer of atmosphere only a few centimeters thick, there is a liquid metal shell several meters thick, and below - a solid crust kilometer thick. The substance of the bark resembles ordinary metal, but is much denser. In the outer part of the crust, it is mainly iron; the fraction of neutrons in its composition increases with depth. Where the density reaches approx. 4Ch 10 11 g/cm 3 , the proportion of neutrons increases so much that some of them are no longer part of the nuclei, but form a continuous medium. There, the substance looks like a "sea" of neutrons and electrons, in which the nuclei of atoms are interspersed. And at a density of approx. 2× 10 14 g/cm 3 (density of the atomic nucleus), individual nuclei disappear altogether and a continuous neutron "liquid" with an admixture of protons and electrons remains. Probably, neutrons and protons behave in this case as a superfluid liquid, similar to liquid helium and superconducting metals in terrestrial laboratories.

neutron star
Neutron star

neutron star - a superdense star formed as a result of a supernova explosion. The substance of a neutron star consists mainly of neutrons.
A neutron star has a nuclear density (10 14 -10 15 g/cm 3) and a typical radius of 10-20 km. Further gravitational contraction of a neutron star is prevented by the pressure of nuclear matter, which arises due to the interaction of neutrons. This pressure of a degenerate much denser neutron gas is able to keep masses up to 3M from gravitational collapse. Thus, the mass of a neutron star varies within (1.4-3)M.

Rice. 1. Cross section of a neutron star with a mass of 1.5M and a radius R = 16 km. The density ρ is given in g/cm 3 in various parts of the star.

Neutrinos produced at the time of the collapse of the supernova, quickly cool the neutron star. Its temperature is estimated to drop from 10 11 to 10 9 K in about 100 s. Further, the rate of cooling decreases. However, it is high on a cosmic scale. The decrease in temperature from 10 9 to 10 8 K occurs in 100 years and to 10 6 K in a million years.
There are ≈ 1200 known objects that belong to neutron stars. About 1000 of them are located within our galaxy. The structure of a neutron star with a mass of 1.5M and a radius of 16 km is shown in Fig. 1: I is a thin outer layer of densely packed atoms. Region II is crystal lattice atomic nuclei and degenerate electrons. Region III is a solid layer of atomic nuclei supersaturated with neutrons. IV - liquid core, consisting mainly of degenerate neutrons. Region V forms the hadronic core of a neutron star. It, in addition to nucleons, can contain pions and hyperons. In this part of a neutron star, the transition of a neutron liquid into a solid is possible. crystalline state, the appearance of pion condensate, the formation of quark-gluon and hyperon plasma. Individual details of the structure of a neutron star are currently being specified.
It is difficult to detect neutron stars with optical methods due to their small size and low luminosity. In 1967, E. Hewish and J. Bell ( Cambridge university) opened space sources periodic radio emission - pulsars. The repetition periods of radio pulses of pulsars are strictly constant and for most pulsars lie in the range from 10 -2 to several seconds. Pulsars are spinning neutron stars. Only compact objects with the properties of neutron stars can retain their shape without collapsing at such rotational speeds. Conservation of angular momentum and magnetic field during the collapse of a supernova and the formation of a neutron star, it leads to the birth of rapidly rotating pulsars with a very strong magnetic field of 10 10 –10 14 G. The magnetic field rotates with the neutron star, however, the axis of this field does not coincide with the axis of rotation of the star. With such a rotation, the radio emission of a star glides across the Earth like a beacon beam. Each time the beam crosses the Earth and hits an observer on Earth, the radio telescope detects a short pulse of radio emission. The frequency of its repetition corresponds to the rotation period of the neutron star. The radiation of a neutron star occurs due to the fact that charged particles (electrons) from the surface of the star move outward along the magnetic field lines, emitting electromagnetic waves. This is the mechanism of radio emission of a pulsar, first proposed by

MOSCOW, August 28 - RIA Novosti. Scientists have discovered a record heavy neutron star with twice the mass of the Sun, which will force them to reconsider a number of theories, in particular, the theory according to which "free" quarks may be present inside the superdense matter of neutron stars, according to an article published on Thursday in journal Nature.

A neutron star is the "corpse" of a star left after a supernova explosion. Its size does not exceed the size small town, however, the density of matter is 10-15 times higher than the density of the atomic nucleus - a "pinch" of neutron star matter weighs more than 500 million tons.

Gravity "presses" electrons into protons, turning them into neutrons, which is why neutron stars got their name. Until recently, scientists believed that the mass of a neutron star cannot exceed two solar masses, because otherwise gravity would "collapse" the star into a black hole. The state of the interior of neutron stars is largely a mystery. For example, the presence of "free" quarks and such elementary particles, like K-mesons and hyperons in central regions neutron star.

The authors of the study, a group of American scientists led by Paul Demorest from the National Radio Observatory, studied double star J1614-2230 is three thousand light-years from Earth, one of whose components is a neutron star and the other a white dwarf.

At the same time, a neutron star is a pulsar, that is, a star that emits narrowly directed radio emission streams; as a result of the rotation of the star, the radiation flux can be caught from the Earth's surface using radio telescopes at different time intervals.

A white dwarf and a neutron star rotate relative to each other. However, the speed of the radio signal from the center of the neutron star is affected by the gravity of the white dwarf, it "slows down" it. Scientists, measuring the time of arrival of radio signals on Earth, can determine with high accuracy the mass of the object "responsible" for the signal delay.

"We are very lucky with this system. A rapidly spinning pulsar gives us a signal coming from an orbit that is perfectly located. Moreover, our white dwarf quite large for stars of this type. This unique combination makes it possible to use the Shapiro effect (gravitational delay of the signal) to its full extent and simplifies measurements," says co-author Scott Ransom.

The binary system J1614-2230 is located in such a way that it can be observed almost edge-on, that is, in the plane of the orbit. This makes it easier to accurately measure the masses of its constituent stars.

As a result, the mass of the pulsar was equal to 1.97 solar masses, which was a record for neutron stars.

"These mass measurements tell us that if there are quarks at all in the core of a neutron star, they cannot be 'free', but most likely they must interact with each other much more strongly than in 'ordinary' atomic nuclei," explains the leader. group of astrophysicists dealing with this issue, Feryal Ozel (Feryal Ozel) from the University of Arizona.

"It surprises me that something as simple as the mass of a neutron star can say so much about various areas physics and astronomy," says Ransom.

Astrophysicist Sergey Popov from the State astronomical institute named after Sternberg notes that the study of neutron stars can give essential information about the structure of matter.

"In terrestrial laboratories, it is impossible to study matter at a density much higher than nuclear. And this is very important for understanding how the world works. Fortunately, this dense matter found in the interiors of neutron stars. To determine the properties of this substance, it is very important to find out what limiting mass a neutron star can have and not turn into a black hole," Popov told RIA Novosti.

Introduction

Throughout its history, mankind has not stopped trying to understand the universe. The universe is called the totality of everything that exists, all the material particles of the space between these particles. By modern ideas The universe is about 14 billion years old.

The size of the visible part of the universe is approximately 14 billion light years (one light year is the distance that light travels in vacuum in one year). According to some scientists, the length of the universe is 90 billion light years. In order to make it convenient to operate with such huge distances, a value called Parsec is used. A parsec is the distance from which average radius Earth's orbit, perpendicular to the line of sight, is visible at an angle of one arc second. 1 parsec = 3.2616 light years.

There is a huge number of different objects in the universe, the names of which are well known to many, such as planets and satellites, stars, black holes, etc. Stars are very diverse in their brightness, size, temperature, and other parameters. Stars include objects such as white dwarfs, neutron stars, giants and supergiants, quasars and pulsars. Of particular interest are the centers of galaxies. According to modern concepts, a black hole is suitable for the role of an object located in the center of a galaxy. Black holes are products of the evolution of stars that are unique in their properties. The experimental validity of the existence of black holes depends on the validity general theory relativity.

In addition to galaxies, the universe is filled with nebulae (interstellar clouds consisting of dust, gas and plasma), background radiation, penetrating the entire universe, and other little-studied objects.

neutron stars

neutron star -- astronomical object, which is one of the end products of the evolution of stars, consisting mainly of a neutron core covered with a relatively thin (~1 km) crust of matter in the form of heavy atomic nuclei and electrons. The masses of neutron stars are comparable to the mass of the Sun, but the typical radius is only 10-20 kilometers. So average density matter of such a star is several times higher than the density of the atomic nucleus (which for heavy nuclei averages 2.8*1017 kg/m?). Further gravitational contraction of a neutron star is prevented by the pressure of nuclear matter, which arises due to the interaction of neutrons.

Many neutron stars have extremely high rotational speeds, up to a thousand revolutions per second. It is believed that neutron stars are born during supernova explosions.

The gravitational forces in neutron stars are balanced by the pressure of the degenerate neutron gas, maximum value the mass of a neutron star is given by the Oppenheimer-Volkov limit, numerical value which depends on the (still poorly known) equation of state of matter in the star's core. There are theoretical prerequisites that, with more higher magnification density, the degeneration of neutron stars into quark stars is possible.

The magnetic field on the surface of neutron stars reaches a value of 1012-1013 Gs (Gs-Gauss - a unit of measurement of magnetic induction), it is the processes in the magnetospheres of neutron stars that are responsible for the radio emission of pulsars. Since the 1990s, some neutron stars have been identified as magnetars, stars with magnetic fields of the order of 1014 gauss and higher. Such fields (exceeding the "critical" value of 4.414 1013 G, at which the interaction energy of an electron with a magnetic field exceeds its rest energy) bring qualitatively new physics, since specific relativistic effects become significant, the polarization physical vacuum etc.

Classification of neutron stars

The two main parameters characterizing the interaction of neutron stars with the surrounding matter and, as a consequence, their observational manifestations are the period of rotation and the magnitude of the magnetic field. Over time, the star spends its rotational energy, and its rotation period increases. The magnetic field is also weakening. For this reason, a neutron star can change its type during its lifetime.

Ejector (radio pulsar) - strong magnetic fields and a small period of rotation. In the simplest model of the magnetosphere, the magnetic field rotates rigidly, that is, with the same angular velocity as the neutron star itself. At a certain radius line speed rotation of the field approaches the speed of light. This radius is called the radius of the light cylinder. Beyond this radius, the usual dipole field cannot exist, so the field strength lines break off at this point. Charged particles moving along magnetic field lines can leave a neutron star through such cliffs and fly away to infinity. A neutron star of this type ejects (spews, pushes out) relativistic charged particles that radiate in the radio range. To an observer, ejectors look like radio pulsars.

Propeller - the rotation speed is already insufficient for the ejection of particles, so such a star cannot be a radio pulsar. However, it is still large, and the matter captured by the magnetic field surrounding the neutron star cannot fall, that is, the accretion of matter does not occur. Neutron stars of this type have practically no observable manifestations and are poorly studied.

Accretor (X-ray pulsar) - the rotation speed is reduced to such an extent that now nothing prevents the substance from falling onto such a neutron star. The plasma, falling, moves along the lines of the magnetic field and hits a solid surface near the poles of a neutron star, heating up to tens of millions of degrees. A substance heated to high temperatures, glows in the X-ray range. The area in which the falling matter collides with the surface of the star is very small - only about 100 meters. This hot spot, due to the rotation of the star, periodically disappears from view, which the observer perceives as pulsations. Such objects are called X-ray pulsars.

Georotator - the rotation speed of such neutron stars is small and does not prevent accretion. But the dimensions of the magnetosphere are such that the plasma is stopped by the magnetic field before it is captured by gravity. A similar mechanism operates in the Earth's magnetosphere, due to which given type and got its name.

December 27, 2004, a burst of gamma rays that arrived at our solar system from SGR 1806-20 (depicted in the artist's view). The explosion was so powerful that it affected the Earth's atmosphere over 50,000 light-years away.

neutron star - cosmic body, which is one of the possible results of evolution, consisting mainly of a neutron core covered with a relatively thin (∼1 km) crust of matter in the form of heavy atomic nuclei and electrons. The masses of neutron stars are comparable to the mass, but the typical radius of a neutron star is only 10-20 kilometers. Therefore, the average density of the substance of such an object is several times higher than the density of the atomic nucleus (which for heavy nuclei is on average 2.8 10 17 kg/m³). Further gravitational contraction of a neutron star is prevented by the pressure of nuclear matter, which arises due to the interaction of neutrons.

Many neutron stars have extremely high rotation speeds - up to a thousand revolutions per second. Neutron stars are created by the explosions of stars.

The masses of most neutron stars with reliably measured masses are 1.3-1.5 solar masses, which is close to the value of the Chandrasekhar limit. Theoretically, neutron stars with masses from 0.1 to about 2.5 solar masses, however, the value of the upper limit mass is currently known very inaccurately. The most massive neutron stars known are Vela X-1 (has a mass of at least 1.88 ± 0.13 solar masses at the 1σ level, which corresponds to a significance level of α≈34%), PSR J1614-2230ruen (with a mass estimate of 1.97 ±0.04 solar), and PSR J0348+0432ruen (with a mass estimate of 2.01±0.04 solar). Gravity in neutron stars is balanced by the pressure of the degenerate neutron gas, the maximum value of the mass of a neutron star is given by the Oppenheimer-Volkov limit, the numerical value of which depends on the (still poorly known) equation of state of matter in the star's core. There are theoretical prerequisites for the fact that with an even greater increase in density, the transformation of neutron stars into quark ones is possible.

Structure of a neutron star.

The magnetic field on the surface of neutron stars reaches a value of 10 12 -10 13 gauss (for comparison, the Earth has about 1 gauss), it is the processes in the magnetospheres of neutron stars that are responsible for the radio emission of pulsars. Since the 1990s, some neutron stars have been identified as magnetars - stars with magnetic fields of the order of 10 14 G and higher. Such magnetic fields (exceeding the “critical” value of 4.414 10 13 G, at which the interaction energy of an electron with a magnetic field exceeds its rest energy mec²) introduce a qualitatively new physics, since specific relativistic effects, polarization of the physical vacuum, etc. become significant.

By 2012, about 2000 neutron stars have been discovered. About 90% of them are single. In total, 10 8 -10 9 neutron stars can exist in ours, that is, somewhere around one per thousand ordinary stars. Neutron stars are characterized by high speeds (usually hundreds of km/s). As a result of the accretion of cloud matter, a neutron star can be seen in this situation in different spectral ranges, including the optical one, which accounts for about 0.003% of the radiated energy (corresponding to magnitude 10).

Gravitational deflection of light (due to relativistic deflection of light, more than half of the surface is visible)

Neutron stars are one of the few classes space objects, which were theoretically predicted before the discovery by observers.

In 1933, astronomers Walter Baade and Fritz Zwicky suggested that a neutron star could form in a supernova explosion. Theoretical calculations of that time showed that the radiation of a neutron star is too weak and impossible to detect. Interest in neutron stars increased in the 1960s, when X-ray astronomy began to develop, as theory predicted that their maximum thermal radiation falls within the soft x-ray area. However, unexpectedly they were discovered in radio observations. In 1967, Jocelyn Bell, a graduate student of E. Hewish, discovered objects that emit regular pulses of radio waves. This phenomenon was explained by the narrow direction of the radio beam from a rapidly rotating object - a kind of "cosmic beacon". But any ordinary star would collapse at such a high rotational speed. Only neutron stars were suitable for the role of such beacons. The pulsar PSR B1919+21 is considered the first discovered neutron star.

The interaction of a neutron star with the surrounding matter is determined by two main parameters and, as a consequence, their observable manifestations: the period (velocity) of rotation and the magnitude of the magnetic field. Over time, the star expends its rotational energy, and its rotation slows down. The magnetic field is also weakening. For this reason, a neutron star can change its type during its lifetime. Below is the nomenclature of neutron stars in descending order of rotation speed, according to the monograph by V.M. Lipunov. Since the theory of pulsar magnetospheres is still in development, there are alternative theoretical models.

Strong magnetic fields and short rotation period. In the simplest model of the magnetosphere, the magnetic field rotates rigidly, that is, with the same angular velocity as the body of a neutron star. At a certain radius, the linear speed of rotation of the field approaches the speed of light. This radius is called the "radius of the light cylinder". Beyond this radius, the usual dipole field cannot exist, so the field strength lines break off at this point. Charged particles moving along lines of force magnetic field, through such cliffs they can leave the neutron star and fly into interstellar space. A neutron star of this type "ejects" (from the French éjecter - to spew, push out) relativistic charged particles that radiate in the radio range. Ejectors are observed as radio pulsars.

Propeller

The rotation speed is already insufficient for particle ejection, so such a star cannot be a radio pulsar. However, the rotation speed is still high, and the matter captured by the magnetic field surrounding the neutron star cannot fall, that is, the accretion of matter does not occur. Neutron stars of this type have practically no observable manifestations and are poorly studied.

Accretor (X-ray pulsar)

The rotation speed is reduced to such a level that now nothing prevents the matter from falling onto such a neutron star. Falling matter, already in the state of plasma, moves along the lines of the magnetic field and hits the solid surface of the body of a neutron star in the region of its poles, heating up to tens of millions of degrees. A substance heated to such high temperatures glows brightly in the X-ray range. The area in which the incident matter collides with the surface of the body of a neutron star is very small - only about 100 meters. This hot spot, due to the rotation of the star, periodically disappears from view, and regular pulsations of X-rays are observed. Such objects are called X-ray pulsars.

Georotator

The rotation speed of such neutron stars is low and does not prevent accretion. But the dimensions of the magnetosphere are such that the plasma is stopped by the magnetic field before it is captured by gravity. A similar mechanism operates in the Earth's magnetosphere, which is why this type of neutron stars got its name.

Magnetar

A neutron star with an exceptionally strong magnetic field (up to 10 11 T). Theoretically, the existence of magnetars was predicted in 1992, and the first evidence of them real existence obtained in 1998 under observation powerful flash gamma and x-ray radiation from the source SGR 1900+14 in the constellation Aquila. The lifetime of magnetars is about 1,000,000 years. Magnetars have the strongest magnetic field in .

Magnetars are a poorly understood type of neutron star due to the fact that few are close enough to Earth. Magnetars in diameter are about 20-30 km, but the masses of most exceed the mass of the Sun. The magnetar is so compressed that a pea of ​​its matter would weigh more than 100 million tons. Most of the known magnetars rotate very quickly, at least a few rotations around the axis per second. They are observed in gamma radiation close to X-rays, they do not emit radio emission. Life cycle magnetar is short enough. Their strong magnetic fields disappear after about 10,000 years, after which their activity and X-ray emission cease. According to one of the assumptions, up to 30 million magnetars could have formed in our galaxy during its entire existence. Magnetars are formed from massive stars with an initial mass of about 40 M☉.

The shocks formed on the surface of the magnetar cause huge fluctuations in a star; the fluctuations in the magnetic field that accompany them often lead to huge bursts of gamma rays, which were recorded on Earth in 1979, 1998 and 2004.

As of May 2007, twelve magnetars were known, and three more candidates were awaiting confirmation. Examples of known magnetars:

SGR 1806-20, located 50,000 light-years from Earth at opposite side our galaxy Milky Way in the constellation Sagittarius.
SGR 1900+14, 20,000 light years distant, located in the constellation Aquila. After long period low emission emissions (significant explosions only in 1979 and 1993) intensified in May-August 1998, and the explosion, detected on August 27, 1998, was strong enough to turn off spacecraft NEAR Shoemaker in order to prevent damage. On May 29, 2008, NASA's Spitzer Telescope detected rings of matter around this magnetar. It is believed that this ring was formed during the explosion observed in 1998.
1E 1048.1-5937 is an anomalous X-ray pulsar located 9000 light years in the constellation Carina. The star from which the magnetar formed had a mass 30-40 times greater than that of the Sun.
A complete list is given in the catalog of magnetars.

As of September 2008, ESO reports the identification of an object originally thought to be a magnetar, SWIFT J195509+261406; it was originally identified by gamma-ray bursts (GRB 070610)