Kevin Gill / flickr.com

German astrophysicists have clarified the maximum possible mass of a neutron star, based on the results of measurements of gravitational waves and electromagnetic radiation from. It turned out that the mass of a non-rotating neutron star cannot be more than 2.16 solar masses, according to an article published in Astrophysical Journal Letters.

Neutron stars are ultra-dense compact stars that form during supernova explosions. The radius of neutron stars does not exceed several tens of kilometers, and their mass can be comparable to the mass of the Sun, which leads to a huge density of star matter (about 10 17 kilograms per cubic meter). At the same time, the mass of a neutron star cannot exceed a certain limit - objects with large masses collapse into black holes under the influence of their own gravity.

By various estimates, upper limit for the mass of a neutron star lies in the range from two to three solar masses and depends on the equation of state of matter, as well as on the speed of rotation of the star. Depending on the density and mass of the star, scientists distinguish several various types stars, a schematic diagram is shown in the figure. First, non-rotating stars cannot have a mass greater than M TOV (white region). Secondly, when a star rotates with constant speed, its mass can be either less than M TOV (light green area) or more (bright green), but still should not exceed another limit, M max. Finally, neutron star with a variable rotation speed can theoretically have an arbitrary mass (red areas of different brightness). However, you should always remember that the density of rotating stars cannot be greater than a certain value, otherwise the star will still collapse into a black hole (the vertical line in the diagram separates stable solutions from unstable ones).

Diagram of different types of neutron stars based on their mass and density. The cross marks the parameters of the object formed after the merger of the stars of the binary system, the dotted lines indicate one of two options for the evolution of the object

L. Rezzolla et al. / The Astrophysical Journal

A team of astrophysicists led by Luciano Rezzolla has set new, more precise limits on the maximum possible mass of a non-rotating neutron star, M TOV. In their work, scientists used data from previous studies, dedicated to processes, which occurred in a system of two merging neutron stars and led to the emission of gravitational (event GW170817) and electromagnetic (GRB 170817A) waves. The simultaneous registration of these waves turned out to be very important event for science, you can read more about it in ours and in the material.

From previous works of astrophysicists, it follows that after the merger of neutron stars, a hypermassive neutron star was formed (that is, its mass M > M max), which subsequently developed according to one of two possible scenarios and after a short period of time turned into a black hole (dashed lines in the diagram ). Observation of the electromagnetic component of the star's radiation points to the first scenario, in which the baryonic mass of the star remains essentially constant and the gravitational mass decreases relatively slowly due to the emission of gravitational waves. On the other hand, the gamma-ray burst from the system arrived almost simultaneously with the gravitational waves (only 1.7 seconds later), which means that the point of transformation into a black hole should lie close to M max.

Therefore, if you trace the evolution of a hypermassive neutron star back to initial state, the parameters of which were calculated with good accuracy in previous works, we can find the value of M max that interests us. Knowing M max, it is not difficult to find M TOV, since these two masses are related by the relation M max ≈ 1.2 M TOV. In this article, astrophysicists performed such calculations using so-called “universal relations,” which relate the parameters of neutron stars of different masses and do not depend on the type of equation of state of their matter. The authors emphasize that their calculations use only simple assumptions and do not rely on numerical simulations. The final result for the maximum possible mass was between 2.01 and 2.16 solar masses. A lower bound for it was previously obtained from observations of massive pulsars in binary systems - simply put, the maximum mass cannot be less than 2.01 solar masses, since astronomers have actually observed neutron stars with such a large mass.

Previously, we wrote about how astrophysicists used computer simulations to estimate the mass and radius of neutron stars, the merger of which led to the events GW170817 and GRB 170817A.

Dmitry Trunin

In astrophysics, as indeed in any other branch of science, the most interesting are evolutionary problems associated with the eternal questions “what happened?” and that will be?". We already know what will happen to a stellar mass approximately equal to the mass of our Sun. Such a star, having gone through a stage red giant, will become white dwarf. White dwarfs on the Hertzsprung-Russell diagram lie off the main sequence.

White dwarfs are the end of the evolution of solar mass stars. They are a kind of evolutionary dead end. Slow and quiet extinction is the end of the road for all stars with a mass less than the Sun. What about more massive stars? We saw that their lives were full of stormy events. But a natural question arises: how do the monstrous cataclysms observed in the form of supernova explosions end?

In 1054, a guest star flashed in the sky. It was visible in the sky even during the day and went out only a few months later. Today we see the remnants of this stellar catastrophe in the form of a bright optical object designated M1 in the Messier Nebula Catalog. This is famous Crab Nebula- remnant of a supernova explosion.

In the 40s of our century, the American astronomer V. Baade began to study central part“Crab” in order to try to find a stellar remnant from a supernova explosion in the center of the nebula. By the way, the name “crab” was given to this object in the 19th century by the English astronomer Lord Ross. Baade found a candidate for a stellar remnant in the form of an asterisk 17t.

But the astronomer was unlucky; he did not have the appropriate equipment for a detailed study, and therefore he could not notice that this star was twinkling and pulsating. If the period of these brightness pulsations were not 0.033 seconds, but, say, several seconds, Baade would undoubtedly have noticed this, and then the honor of discovering the first pulsar would not have belonged to A. Hewish and D. Bell.

About ten years before Baade pointed his telescope at the center Crab Nebula, theoretical physicists began to study the state of matter at densities exceeding the density of white dwarfs (106 - 107 g/cm3). Interest in this issue arose in connection with the problem of the final stages of stellar evolution. It is interesting that one of the co-authors of this idea was the same Baade, who connected the very fact of the existence of a neutron star with a supernova explosion.

If matter is compressed to densities greater than those of white dwarfs, so-called neutronization processes begin. The monstrous pressure inside the star “drives” electrons into atomic nuclei. IN normal conditions a nucleus that has absorbed electrons will be unstable because it contains an excess number of neutrons. However, this is not the case in compact stars. As the density of the star increases, the electrons of the degenerate gas are gradually absorbed by the nuclei, and little by little the star turns into a giant neutron star- a drop. The degenerate electron gas is replaced by a degenerate neutron gas with a density of 1014-1015 g/cm3. In other words, the density of a neutron star is billions of times greater than that of a white dwarf.

For a long time, this monstrous configuration of the star was considered a trick of theorists' minds. It took more than thirty years for nature to confirm this outstanding prediction. In the same 30s, another one was made important discovery, which had a decisive influence on the entire theory of stellar evolution. Chandrasekhar and L. Landau established that for a star that has exhausted sources of nuclear energy, there is a certain limiting mass when the star still remains stable. At this mass, the pressure of the degenerate gas is still able to resist the forces of gravity. As a consequence, the mass of degenerate stars (white dwarfs, neutron stars) has a finite limit (Chandrasekhar limit), exceeding which causes catastrophic compression of the star, its collapse.

Note that if the core mass of a star is between 1.2 M and 2.4 M, the final “product” of the evolution of such a star should be a neutron star. With a core mass of less than 1.2 M, evolution will ultimately lead to the birth of a white dwarf.

What is a neutron star? We know its mass, we also know that it consists mainly of neutrons, the sizes of which are also known. From here it is easy to determine the radius of the star. It turns out to be close to... 10 kilometers! Determining the radius of such an object is indeed not difficult, but it is very difficult to visualize that a mass close to the mass of the Sun can be placed in an object whose diameter is slightly larger than the length of Profsoyuznaya Street in Moscow. This is a giant nuclear drop, the supernucleus of an element that does not fit into any periodic systems and has an unexpected, peculiar structure.

The matter of a neutron star has the properties of a superfluid liquid! This fact is hard to believe at first glance, but it is true. The substance, compressed to monstrous densities, resembles to some extent liquid helium. In addition, we should not forget that the temperature of a neutron star is about a billion degrees, and, as we know, superfluidity in terrestrial conditions appears only at ultra-low temperatures.

True, temperature does not play a special role in the behavior of the neutron star itself, since its stability is determined by the pressure of the degenerate neutron gas - liquid. The structure of a neutron star is in many ways similar to the structure of a planet. In addition to the “mantle”, consisting of a substance with the amazing properties of a superconducting liquid, such a star has a thin, hard crust about a kilometer thick. It is assumed that the bark has a peculiar crystalline structure. Peculiar because, unlike crystals known to us, where the structure of the crystal depends on the configuration electronic shells atom, in the crust of a neutron star, atomic nuclei are devoid of electrons. Therefore, they form a lattice reminiscent of the cubic lattices of iron, copper, zinc, but, accordingly, at immeasurably higher densities. Next comes the mantle, the properties of which we have already talked about. At the center of a neutron star, densities reach 1015 grams per cubic centimeter. In other words, a teaspoon of the material from such a star weighs billions of tons. It is assumed that at the center of the neutron star there occurs continuing education all known in nuclear physics, as well as not yet discovered exotic elementary particles.

Neutron stars cool quite quickly. Estimates show that over the first ten to one hundred thousand years the temperature drops from several billion to hundreds of millions of degrees. Neutron stars rotate rapidly, and this leads to a number of very interesting consequences. By the way, it is the small size of the star that allows it to remain intact during rapid rotation. If its diameter were not 10, but, say, 100 kilometers, it would simply be torn apart by centrifugal forces.

We have already talked about the intriguing history of the discovery of pulsars. The idea was immediately put forward that the pulsar was a rapidly rotating neutron star, since of all the known stellar configurations, only it could remain stable, rotating at high speed. It was the study of pulsars that made it possible to come to the remarkable conclusion that neutron stars, discovered “at the tip of the pen” by theorists, actually exist in nature and they arise as a result of supernova explosions. The difficulties of detecting them in the optical range are obvious, since due to their small diameter, most neutron stars cannot be seen at the most powerful telescopes, although, as we have seen, there are exceptions here - a pulsar in Crab Nebula.

So, astronomers discovered new class objects - pulsars, rapidly rotating neutron stars. A natural question arises: what is the reason for such a rapid rotation of a neutron star, why, in fact, should it spin around its axis at enormous speed?

The reason for this phenomenon is simple. We know well how a skater can increase the speed of rotation when he presses his arms closer to his body. In doing so, he uses the law of conservation of angular momentum. This law is never violated, and it is precisely this law that, during a supernova explosion, increases the rotation speed of its remnant, the pulsar, many times over.

Indeed, during the collapse of a star, its mass (what is left after the explosion) does not change, but the radius decreases by about a hundred thousand times. But the angular momentum, equal to the product of the equatorial rotation speed by the mass and the radius, remains the same. The mass does not change, therefore, the speed must increase by the same hundred thousand times.

Let's look at a simple example. Our Sun rotates quite slowly around its own axis. The period of this rotation is approximately 25 days. So, if the Sun suddenly became a neutron star, its rotation period would decrease to one ten-thousandth of a second.

The second important consequence of conservation laws is that neutron stars must be very strongly magnetized. In fact, in any natural process we cannot simply destroy the magnetic field (if it already exists). Magnetic field lines are forever associated with the stellar matter, which has excellent electrical conductivity. The magnitude of the magnetic flux on the surface of the star is equal to the product of the magnitude of the intensity magnetic field per square of the radius of the star. This value is strictly constant. That is why, when a star contracts, the magnetic field should increase very strongly. Let us dwell on this phenomenon in some detail, since it is this phenomenon that determines many of the amazing properties of pulsars.

The magnetic field strength can be measured on the surface of our Earth. We will get a small value of about one gauss. In a good physics laboratory, magnetic fields of a million gauss can be obtained. On the surface of white dwarfs, the magnetic field strength reaches one hundred million gauss. Nearby the field is even stronger - up to ten billion gauss. But on the surface of a neutron star, nature reaches an absolute record. Here the field strength can be hundreds of thousands of billions of gauss. The void in a liter jar containing such a field would weigh about a thousand tons.

Such strong magnetic fields cannot but affect (of course, in combination with the gravitational field) the nature of the interaction of the neutron star with the surrounding matter. After all, we have not yet talked about why pulsars have enormous activity, why they emit radio waves. And not only radio waves. Today, astrophysicists are well aware of X-ray pulsars observed only in binary systems, gamma-ray sources with unusual properties, the so-called X-ray bursters.

To imagine the various mechanisms of interaction of a neutron star with matter, let us turn to the general theory of slow changes in the modes of interaction of neutron stars with environment. Let us briefly consider the main stages of such evolution. Neutron stars - remnants of supernova explosions - initially rotate very quickly with a period of 10 -2 - 10 -3 seconds. With such rapid rotation, the star emits radio waves, electromagnetic radiation, and particles.

One of the most amazing properties pulsars is the monstrous power of their radiation, billions of times greater than the power of radiation from the stellar interior. For example, the radio emission power of the pulsar in the “Crab” reaches 1031 erg/sec, in optics - 1034 erg/sec, which is much more than the emission power of the Sun. This pulsar emits even more in the X-ray and gamma-ray ranges.

How do these natural energy generators work? All radio pulsars have one common property, which served as the key to unraveling the mechanism of their action. This property lies in the fact that the period of pulse emission does not remain constant, it slowly increases. It is worth noting that this property of rotating neutron stars was first predicted by theorists, and then very quickly confirmed experimentally. Thus, in 1969 it was found that the period of emission of pulsar pulses in the “Crab” is growing by 36 billionths of a second per day.

We will not talk now about how such short periods of time are measured. What is important for us is the very fact of increasing the period between pulses, which, by the way, makes it possible to estimate the age of pulsars. But still, why does a pulsar emit pulses of radio emission? This phenomenon has not been fully explained within the framework of any complete theory. But a qualitative picture of the phenomenon can nevertheless be drawn.

The thing is that the axis of rotation of a neutron star does not coincide with its magnetic axis. It is well known from electrodynamics that if a magnet is rotated in a vacuum around an axis that does not coincide with the magnetic one, then electromagnetic radiation will arise exactly at the frequency of rotation of the magnet. At the same time, the rotation speed of the magnet will slow down. This is understandable from general considerations, since if braking did not occur, we would simply have a perpetual motion machine.

Thus, our transmitter draws the energy of radio pulses from the rotation of the star, and its magnetic field is like a driving belt of a machine. The real process is much more complicated, since a magnet rotating in a vacuum is only partially an analogue of a pulsar. After all, a neutron star does not rotate in a vacuum; it is surrounded by a powerful magnetosphere, a plasma cloud, and this good guide, making its own adjustments to the simple and rather schematic picture we have drawn. As a result of the interaction of the pulsar’s magnetic field with the surrounding magnetosphere, narrow beams of directed radiation are formed, which, with a favorable “location of the stars,” can be observed in various parts of the galaxy, in particular on Earth.

The rapid rotation of a radio pulsar at the beginning of its life causes not only radio emission. A significant portion of the energy is also carried away by relativistic particles. As the pulsar's rotation speed decreases, the radiation pressure drops. Previously, the radiation had pushed the plasma away from the pulsar. Now the surrounding matter begins to fall on the star and extinguishes its radiation. This process can be especially effective if the pulsar is part of a binary system. In such a system, especially if it is close enough, the pulsar pulls the matter of the “normal” companion onto itself.

If the pulsar is young and full of energy, its radio emission is still able to “break through” to the observer. But the old pulsar is no longer able to fight the accretion, and it “extinguishes” the star. As the pulsar's rotation slows, other remarkable processes begin to appear. Since the gravitational field of a neutron star is very powerful, the accretion of matter releases a significant amount of energy in the form of X-rays. If in a binary system the normal companion contributes a noticeable amount of matter to the pulsar, approximately 10 -5 - 10 -6 M per year, the neutron star will be observed not as a radio pulsar, but as an X-ray pulsar.

But that is not all. In some cases, when the magnetosphere of a neutron star is close to its surface, matter begins to accumulate there, forming a kind of shell of the star. In this shell, favorable conditions can be created for thermonuclear reactions to occur, and then we can see an X-ray burster in the sky (from English word burst - “flash”).

As a matter of fact, this process should not look unexpected to us; we have already talked about it in relation to white dwarfs. However, the conditions on the surface of a white dwarf and a neutron star are very different, and therefore X-ray bursters are clearly associated with neutron stars. Thermo nuclear explosions are observed by us in the form of X-ray flares and, perhaps, gamma-ray bursts. Indeed, some gamma-ray bursts may appear to be caused by thermonuclear explosions on the surface of neutron stars.

But let's return to X-ray pulsars. The mechanism of their radiation, naturally, is completely different from that of bursters. Nuclear energy sources no longer play any role here. The kinetic energy of the neutron star itself also cannot be reconciled with observational data.

Let's take the X-ray source Centaurus X-1 as an example. Its power is 10 erg/sec. Therefore, the reserve of this energy could only be enough for one year. In addition, it is quite obvious that the rotation period of the star in this case would have to increase. However, for many X-ray pulsars, unlike radio pulsars, the period between pulses decreases over time. This means that the issue here is not the kinetic energy of rotation. How do X-ray pulsars work?

We remember that they manifest themselves in double systems. It is there that accretion processes are especially effective. The speed at which matter falls onto a neutron star can reach one third the speed of light (100 thousand kilometers per second). Then one gram of the substance will release the energy of 1020 erg. And to ensure an energy release of 1037 erg/sec, it is necessary that the flow of matter onto the neutron star be 1017 grams per second. This, in general, is not very much, about one thousandth of the Earth’s mass per year.

The material supplier may be an optical companion. A stream of gas will continuously flow from part of its surface towards the neutron star. It will supply both energy and matter to the accretion disk formed around the neutron star.

Because a neutron star has a huge magnetic field, gas will “flow” along magnetic field lines towards the poles. It is there, in relatively small “spots” of the order of only one kilometer in size, that grandiose-scale processes of the creation of powerful X-ray radiation take place. X-rays are emitted by relativistic and ordinary electrons moving in the magnetic field of the pulsar. The gas falling on it can also “feed” its rotation. That is why it is precisely in X-ray pulsars that a decrease in the rotation period is observed in a number of cases.

X-ray sources included in dual systems, is one of the most remarkable phenomena in space. There are few of them, probably no more than a hundred in our Galaxy, but their significance is enormous not only from the point of view, in particular for understanding type I. Binary systems provide the most natural and efficient way for matter to flow from star to star, and it is here (due to the relatively rapid change in the mass of stars) that we may encounter various options"accelerated" evolution.

Another interesting consideration. We know how difficult, almost impossible, it is to estimate the mass of a single star. But since neutron stars are part of binary systems, it may turn out that sooner or later it will be possible to empirically (and this is extremely important!) determine the maximum mass of a neutron star, as well as obtain direct information about its origin.

Introduction

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

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 a vacuum in one year). Some scientists estimate the extent of the universe to be 90 billion light years. In order to make it convenient to operate such huge distances, a value called Parsec is used. A parsec is the distance from which the average radius of the Earth's orbit, perpendicular to the line of sight, is visible at an angle of one arcsecond. 1 parsec = 3.2616 light years.

There are a huge number of different objects in the universe, the names of which are familiar 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 ideas, a black hole is suitable for the role of the object located in the center of the galaxy. Black holes are products of the evolution of stars that are unique in their properties. The experimental reliability of the existence of black holes depends on the validity of the general theory of relativity.

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

Neutron stars

A neutron star is an astronomical object, which is one of the final 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. Therefore, the average density of the matter of such a star is several times higher than the density of the atomic nucleus (which for heavy nuclei is on average 2.8 * 1017 kg/m?). Further gravitational compression of the neutron star is prevented by the pressure of nuclear matter arising due to the interaction of neutrons.

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

Gravitational forces in neutron stars are balanced by the pressure of the degenerate neutron gas, the maximum value of the mass of a neutron star is set 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 premises that with an even greater increase in density, the degeneration of neutron stars into quarks is possible.

The magnetic field on the surface of neutron stars reaches a value of 1012-1013 G (Gauss is a unit of measurement of magnetic induction), and 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 or higher. Such fields (exceeding the “critical” value of 4.414 1013 G, at which the energy of interaction of an electron with a magnetic field exceeds its rest energy) introduce qualitatively new physics, since specific relativistic effects, polarization of the physical vacuum, etc. become significant.

Classification of neutron stars

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

Ejector (radio pulsar) - strong magnetic fields and short rotation period. IN the simplest model magnetosphere, the magnetic field rotates solidly, that is, with the same angular velocity, which is the same as the neutron star itself. 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, an ordinary dipole field cannot exist, so the field strength lines break off at this point. Charged particles moving along magnetic field lines can leave the neutron star through such cliffs and fly away to infinity. A neutron star of this type ejects (spews out) relativistic charged particles that emit in the radio range. To an observer, ejectors look like radio pulsars.

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

Accretor (X-ray pulsar) - the rotation speed is reduced to such an extent that nothing now prevents matter from falling onto such a neutron star. The plasma, falling, moves along the magnetic field lines and hits a solid surface in the region of the poles of the neutron star, heating up to tens of millions of degrees. A substance heated to such a high temperatures, glows in the X-ray range. The region in which the collision of falling matter with the surface of the star occurs is very small - only about 100 meters. Due to the rotation of the star, this hot spot 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 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 got its name.

Neutron star
Neutron star

Neutron star - a super-dense star formed as a result of a supernova explosion. The matter 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 compression of the neutron star is prevented by the pressure of nuclear matter arising due to the interaction of neutrons. This pressure of the degenerate significantly denser neutron gas is able to keep masses up to 3M from gravitational collapse.

Thus, the mass of a neutron star varies within the range of (1.4-3)M.

Rice. 1. Cross-section of a neutron star with a mass of 1.5M and a radius of R = 16 km. The density ρ is indicated in g/cm 3 in different parts of the star.
There are approximately 1200 known objects that are classified as 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 – thin outer layer of densely packed atoms. Region II is a crystal lattice of 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 the neutron star. In addition to nucleons, it can contain pions and hyperons. In this part of the neutron star, the transition of the neutron liquid into a solid crystalline state, the appearance of a pion condensate, and the formation of quark-gluon and hyperon plasma are possible. Certain details of the structure of a neutron star are currently being clarified. Detect neutron stars

optical methods Scientists have discovered a record-heavy neutron star with twice the mass of the Sun, forcing them to reconsider a number of theories, in particular the theory that there may be "free" quarks inside the super-dense matter of neutron stars, according to a paper published Thursday in journal Nature.

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

Gravity “presses” electrons into protons, turning them into neutrons, which is why neutron stars get their name. Until recently, scientists believed that the mass of a neutron star could not exceed two solar masses, since 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 as K-mesons and hyperons in the central regions of a neutron star is discussed.

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

In this case, a neutron star is a pulsar, that is, a star emitting narrowly directed fluxes of radio emission; as a result of the star’s rotation, the radiation flux can be detected from the Earth’s surface using radio telescopes at different time intervals.

The white dwarf and neutron star rotate relative to each other. However, the speed of passage of a radio signal from the center of a neutron star is affected by the gravity of the white dwarf; it “slows down” it. Scientists, by measuring the arrival time of radio signals on Earth, can accurately determine the mass of the object “responsible” for the signal delay.

"We are very lucky with this system. The rapidly spinning pulsar gives us a signal coming from an orbit that is perfectly positioned. Moreover, our white dwarf is quite large for stars of this type. This unique combination allows us to take full advantage of the Shapiro effect (gravitational delay of the signal) and simplifies measurements,” says one of the authors of the paper, 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 orbital plane. This makes it easier to accurately measure the masses of its constituent stars.

As a result, the mass of the pulsar turned out to be equal to 1.97 solar masses, which became 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 must interact with each other much stronger than in “ordinary” ones. atomic nuclei", explains the leader of the group of astrophysicists working on this issue, Feryal Ozel from Arizona State University.

"It's amazing to me that something as simple as the mass of a neutron star can tell so much in different areas of physics and astronomy," Ransom says.

Astrophysicist Sergei Popov from the Sternberg State Astronomical Institute notes that the study of neutron stars can provide vital information about the structure of matter.

“In earthly laboratories it is impossible to study matter at a density much greater than nuclear density. And this is very important for understanding how the world works. Fortunately, this dense substance exists in the depths of neutron stars. To determine the properties of this substance, it is very important to find out what maximum mass a neutron star can have without turning into a black hole,” Popov told RIA Novosti.