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 averages 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 are acceptable, but the value of the upper mass limit 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 accretion of cloud matter, a neutron star can be seen in this situation in different spectral ranges, including optical, which accounts for about 0.003% of the radiated energy (corresponding to 10 magnitude).
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 of cosmic objects that were theoretically predicted prior to 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 the maximum of their thermal radiation occurred in the soft X-ray region. 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 magnetic field lines can leave a neutron star through such cliffs and fly away 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 periodically disappears from view due to the rotation of the star, 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 their real existence was obtained in 1998 when observing a powerful flash of 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 oscillations in the star; the magnetic field fluctuations that accompany them often lead to huge gamma-ray bursts that 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 a long period of 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 force the NEAR Shoemaker spacecraft to turn off 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)
NEUTRON STAR
a star made up mostly of neutrons. A neutron is a neutral subatomic particle, one of the main constituents of matter. 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.
see also PULSAR. 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 of an 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 a neutron star becomes more than about 2 solar masses, then gravity will exceed this pressure and the star will not be able to withstand the collapse.
see also GRAVITATIONAL 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). WITH neutron stars connect celestial objects of 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 to tremendous speed. When hitting the surface of a neutron star, the gas releases 10-30% of its rest energy, while in nuclear reactions this figure does not even reach 1%. The surface of a neutron star heated to a high temperature becomes a source of X-rays. 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 of a kilometer thickness. 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. 4*10 11 g/cm3, the fraction of neutrons increases so much that some of them are no longer part of the nuclei, but form a continuous medium. There, the matter 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/cm3 (the 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.
With even more high densities in a neutron star, the most unusual forms of matter are formed. Maybe neutrons and protons decay into even smaller particles - quarks; it is also possible that many pi-mesons are produced, which form the so-called pion condensate.
see also
PARTICLES ELEMENTARY;
SUPERCONDUCTIVITY ;
SUPERFLUIDITY.
LITERATURE
Dyson F., Ter Haar D. Neutron stars and pulsars. M., 1973 Lipunov V.M. Astrophysics of neutron stars. M., 1987
Collier Encyclopedia. - Open society. 2000 .
See what "NEUTRON STAR" is in other dictionaries:
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Neutron star concept
The concept of neutron stars is not new: the first suggestion about the possibility of their existence was made by talented astronomers Fritz Zwicky and Walter Baarde from California in 1934. (Somewhat earlier, in 1932, the possibility of the existence of neutron stars was predicted by the famous Soviet scientist L. D. Landau.) In the late 1930s, it became the subject of research by other American scientists Oppenheimer and Volkov. The interest of these physicists in this problem was caused by the desire to determine the final stage of the evolution of a massive contracting star. Since the role and significance of supernovae was revealed around the same time, it was suggested that a neutron star could be the remnant of a supernova explosion. Unfortunately, with the outbreak of the Second World War, the attention of scientists switched to military needs and a detailed study of these new and the highest degree mysterious objects has been suspended. Then, in the 50s, the study of neutron stars was resumed purely theoretically in order to establish whether they are relevant to the problem of birth chemical elements in the central regions of stars.remain the only astrophysical object whose existence and properties were predicted long before their discovery.
In the early 1960s, the discovery of cosmic X-ray sources greatly encouraged those who considered neutron stars as possible sources of celestial X-rays. By the end of 1967 a new class of celestial objects, pulsars, was discovered, which confused scientists. This discovery was the most important event in the study of neutron stars, since it again raised the question of the origin of cosmic X-rays. Speaking of neutron stars, it should be borne in mind that their physical characteristics established theoretically and very hypothetically, since the physical conditions existing in these bodies cannot be reproduced in laboratory experiments.
Properties of neutron stars
Gravitational forces play a decisive role in the properties of neutron stars. According to various estimates, the diameters of neutron stars are 10-200 km. And this volume, insignificant according to cosmic concepts, is "stuffed" with such an amount of substance that can be heavenly body, similar to the Sun, with a diameter of about 1.5 million km, and in mass almost a third of a million times heavier than the Earth! A natural consequence of this concentration of matter is the incredibly high density of a neutron star. In fact, it turns out to be so dense that it can even be solid. The gravity of a neutron star is so great that a person would weigh about a million tons there. Calculations show that neutron stars are highly magnetized. According to estimates, the magnetic field of a neutron star can reach 1 million km. million gauss, while on Earth it is 1 gauss. Neutron star radius about 15 km is taken, and the mass is about 0.6 - 0.7 solar masses. The outer layer is a magnetosphere consisting of rarefied electron and nuclear plasma, which is penetrated by a powerful magnetic field of the star. It is here that radio signals are born, which are hallmark pulsars. Ultrafast charged particles, moving in spirals along magnetic field lines, give rise to various kinds of radiation. In some cases, radiation occurs in the radio range of the electromagnetic spectrum, in others - radiation at high frequencies.Density of a neutron star
Almost immediately below the magnetosphere, the density of matter reaches 1 t/cm3, which is 100,000 times greater than the density of iron. The next outer layer has the characteristics of a metal. This layer of "superhard" matter is in crystalline form. Crystals are made up of atomic nuclei atomic mass 26 - 39 and 58 - 133. These crystals are extremely small: to cover a distance of 1 cm, you need to line up about 10 billion crystals in one line. The density in this layer is more than 1 million times higher than in the outer layer, or otherwise, 400 billion times higher than the density of iron.Moving further towards the center of the star, we cross the third layer. It includes a region of heavy nuclei such as cadmium, but is also rich in neutrons and electrons. The density of the third layer is 1,000 times greater than the previous one. Penetrating deeper into a neutron star, we reach the fourth layer, while the density increases slightly - about five times. Nevertheless, with such a density, the nuclei can no longer maintain their physical integrity: they decay into neutrons, protons and electrons. Most of the matter is in the form of neutrons. There are 8 neutrons for every electron and proton. This layer, in essence, can be considered as a neutron liquid "polluted" by electrons and protons. Below this layer is the core of a neutron star. Here the density is about 1.5 times greater than in the overlying layer. And yet, even this small increase in density causes the particles in the core to move much faster than in any other layer. The kinetic energy of the motion of neutrons mixed with a small amount of protons and electrons is so great that inelastic collisions of particles constantly occur. In the processes of collision, all particles and resonances known in nuclear physics are born, of which there are more than a thousand. In all likelihood, there is big number particles not yet known to us.
Neutron star temperature
The temperatures of neutron stars are comparatively high. This is to be expected, given how they arise. During the first 10 - 100 thousand years of the existence of a star, the temperature of the core decreases to several hundred million degrees. Then comes a new phase, when the temperature of the star's core slowly decreases due to the emission of electromagnetic radiation.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 of an 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). Two different types of celestial objects are associated with neutron stars.
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 to tremendous speed. When hitting the surface of a neutron star, the gas releases 10-30% of its rest energy, while in nuclear reactions this figure does not even reach 1%. The surface of a neutron star heated to a high temperature becomes a source of X-rays. However, the fall of gas does not occur uniformly over the entire surface: the strong magnetic field of a neutron star captures the falling ionized gas and directs it to the magnetic poles, where it falls, like into 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.
At sufficiently high densities, the equilibrium of the star begins to break down neutronization process stellar matter. As is known, during the b - -decay of a nucleus, part of the energy is carried away by an electron, and the rest is a neutrino. This total energy determines upper energy of b - -decay. In the case when the Fermi energy exceeds the upper energy of b - -decay, then the process opposite to b - -decay becomes very probable: the nucleus absorbs an electron (electron capture). As a result of a sequence of such processes, the concentration of electrons in the star decreases, and the pressure of the degenerate electron gas, which maintains the star in equilibrium, also decreases. This leads to further gravitational contraction of the star, and with it to a further increase in the average and maximum energy of the degenerate electron gas - the probability of electron capture by nuclei increases. In the end, neutrons can accumulate so much that the star will consist mainly of neutrons. Such stars are called neutron. A neutron star cannot be composed of neutrons alone, as the pressure of the electron gas is needed to prevent the neutrons from becoming protons. A neutron star contains a small admixture (about 1¸2%) of electrons and protons. Due to the fact that neutrons do not experience Coulomb repulsion, the average density of matter inside a neutron star is very high - approximately the same as in atomic nuclei. At this density, the radius of a neutron star with a mass on the order of the sun is approximately 10 km. Theoretical calculations on models show that the upper limit of the mass of a neutron star is determined by the estimation formula M pr "( 2-3)M Q .
Calculations show that the explosion of a supernova with M ~ 25M Q leaves a dense neutron core (neutron star) with a mass of ~ 1.6M Q . In stars with a residual mass M > 1.4M Q that have not reached the supernova stage, the pressure of the degenerate electron gas is also unable to balance the gravitational forces, and the star shrinks to the state of nuclear density. The mechanism of this gravitational collapse is the same as in a supernova explosion. The pressure and temperature inside the star reach such values at which electrons and protons seem to be “pressed” into each other and, as a result of the reaction ( p + e - ®n + n e) after the ejection of neutrinos, neutrons are formed, which occupy a much smaller phase volume than electrons. A so-called neutron star appears, the density of which reaches 10 14 - 10 15 g/cm 3 . The characteristic size of a neutron star is 10 - 15 km. In a sense, a neutron star is a giant atomic nucleus. Further gravitational contraction is prevented by the pressure of nuclear matter, which arises due to the interaction of neutrons. This is also the degeneracy pressure, as earlier in the case of a white dwarf, but is the degeneracy pressure of a much denser neutron gas. This pressure is able to hold masses up to 3.2M Q
The neutrinos produced at the moment of collapse cool the neutron star rather quickly. According to theoretical estimates, its temperature drops from 10 11 to 10 9 K in ~ 100 s. Further, the rate of cooling decreases somewhat. However, it is quite high in astronomical terms. The decrease in temperature from 10 9 to 10 8 K occurs in 100 years and to 10 6 K in a million years. Detecting neutron stars with optical methods is quite difficult due to their small size and low temperature.
In 1967, at the University of Cambridge, Hewish and Bell discovered cosmic sources of periodic electromagnetic radiation - pulsars. The pulse repetition periods of most pulsars lie in the range from 3.3·10 -2 to 4.3 s. According to modern ideas, pulsars are rotating neutron stars with a mass of 1 - 3M Q and a diameter of 10 - 20 km. Only compact objects with the properties of neutron stars can maintain their shape without collapsing at such rotational speeds. The conservation of angular momentum and magnetic field during the formation of a neutron star leads to the birth of rapidly rotating pulsars with a strong magnetic field IN magn ~ 10 12 gauss.
It is believed that a neutron star has a magnetic field whose axis does not coincide with the axis of rotation of the star. In this case, the radiation of the star (radio waves and visible light) glides across the Earth like the rays of a beacon. When the beam crosses the Earth, an impulse is registered. The very radiation of a neutron star arises due to the fact that charged particles from the surface of the star move outward along lines of force magnetic field, emitting electromagnetic waves. This model of the radio emission mechanism of a pulsar, first proposed by Gold, is shown in Fig. 9.6.
Rice. 9.6. Pulsar model.
If the radiation beam hits an earthly observer, then the radio telescope detects short pulses of radio emission with a period equal to the rotation period of the neutron star. The shape of the pulse can be very complex, which is due to the geometry of the magnetosphere of a neutron star and is characteristic of each pulsar. The rotation periods of pulsars are strictly constant and the measurement accuracy of these periods reaches 14-digit figures.
Pulsars that are part of binary systems have now been discovered. If the pulsar orbits around the second component, then variations in the period of the pulsar due to the Doppler effect should be observed. When the pulsar approaches the observer, the recorded period of radio pulses decreases due to the Doppler effect, and when the pulsar moves away from us, its period increases. Based on this phenomenon, pulsars that are part of binary stars were discovered. For the first discovered pulsar PSR 1913 + 16, which is part of a binary system, the orbital period of revolution was 7 hours 45 minutes. The proper period of revolution of the pulsar PSR 1913 + 16 is 59 ms.
The radiation of the pulsar should lead to a decrease in the speed of rotation of the neutron star. This effect has also been found. A neutron star, which is part of a binary system, can also be a source of intense X-rays. The structure of a neutron star with a mass of 1.4M Q and a radius of 16 km is shown in fig. 9.7 .
I - thin outer layer of densely packed atoms. In regions II and III, the nuclei are arranged in the form of a body-centered cubic lattice. Region IV consists mainly of neutrons. In region V, matter can consist of pions and hyperons, forming the hadronic core of a neutron star. Individual details of the structure of a neutron star are currently being specified.
