Stars whose mass is 1.5-3 times greater than that of the Sun will not be able to stop their compression at the stage of a white dwarf at the end of their lives. Powerful gravitational forces will squeeze them to such a density at which a “neutralization” of the substance takes place: the interaction of electrons with protons will lead to the fact that almost the entire mass of the star will be enclosed in neutrons. A neutron star is formed. The most massive stars can form into neutron stars after they explode like supernovae.
The concept of neutron stars is not new: the first assumption about the possibility of their existence was made by the talented astronomers Fritz Zwicky and Walter Baarde of California in 1934. (A little earlier in 1932, the possibility of the existence of neutron stars was predicted by the famous Soviet scientists L.D. Landau.) In the late 30s, 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 evolution of a massive contracting star. Since the role and significance of supernovae opened up at about the same time, it was suggested that a neutron star could be the remnant of a supernova explosion. Unfortunately, with the outbreak of World War II, scientists turned their attention to military needs and a detailed study of these new and highly mysterious objects was suspended. Then, in the 50s, the study of neutron stars was resumed purely theoretically in order to establish whether they are related to the problem of the birth of chemical elements in the central regions of stars. Neutron stars remain the only astrophysical object whose existence and properties were predicted long before their discovery.
In the early 60s, the discovery of cosmic x-ray sources was very encouraging for those who considered neutron stars as possible sources of celestial x-ray radiation. By the end of 1967 a new class of celestial objects was discovered – pulsars, which confused scientists. This discovery was the most important event in the study of neutron stars, as it again raised the question of the origin of cosmic x-ray radiation.
Speaking of neutron stars, it should be borne in mind that their physical characteristics are established theoretically and are very hypothetical, since the physical conditions existing in these bodies cannot be reproduced in laboratory experiments.
Crucial to the properties of neutron stars are gravitational forces. According to various estimates, the diameters of neutron stars are 10-200 km. And this volume, insignificant in cosmic concepts, is “filled” with such an amount of matter that can make up a celestial body, like the Sun, with a diameter of about 1.5 million km, and by mass almost a third 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. million Gauss, while on Earth it is 1 Gauss. The radius of a neutron star is assumed to be about 15 km, and the mass is about 0.6 – 0.7 the mass of the Sun. The outer layer is a magnetosphere consisting of a rarefied electron and nuclear plasma, which is penetrated by a powerful magnetic field of a star. It is here that radio signals originate, which are the hallmark of pulsars. Superfast charged particles moving in spirals along magnetic lines of force give rise to all kinds of radiation. In some cases, radiation occurs in the radio range of the electromagnetic spectrum, in others – radiation at high frequencies. Almost immediately under the magnetosphere, the density of the substance reaches 1 t / cm3, which is 100,000 times higher than the density of iron.
Following the outer layer has the characteristics of a metal. This layer is a “superhard” substance in crystalline form. The crystals consist of nuclei of atoms with an atomic mass of 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 a line. The density in this layer is more than 1 million times higher than in the outer, or else, 400 billion times higher than the density of iron. Moving further to the center of the star, we cross the third layer. It includes a region of heavy cadmium-type nuclei, but is also rich in neutrons and electrons. The density of the third layer is 1,000 times greater than the previous.
Penetrating deeper into the neutron star, we reach the fourth layer, while the density increases slightly – about five times. However, with such a density, 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 per electron and proton.