What are neutron stars made of? What is the ultimate density?

The universe is full of miracles. At present, human beings know very little about the universe. There are still many unknowns in the universe that need us to continue to explore. Today we are going to learn about neutron stars, so let's use constellation knowledge to reveal what neutron stars are. What is it made of?

The limit density of neutron stars The typical neutron star density is as high as 1 100 million ~ 1 100 million tons/cubic centimeter, which has far exceeded the density of the earth's matter, equivalent to a white dwarf matter the size of a dice, and equivalent to the mass of a mountain. If the earth is compressed to the density of a neutron star, its diameter is only about 20 meters.

What are neutron stars made of? Neutron stars are one of the possible outcomes of massive stars. When a star burns its core nuclear fusion material (fused into iron), because there is no heat to resist the gravity of the star, the star shrinks at a high speed (gravitational collapse), and these star materials will collide together at the core, producing iron and subsequent nuclear fusion reactions, and emitting the brightness of more than one galaxy. This is a supernova explosion. The explosion will last for weeks to months, during which a large number of elements after iron will be synthesized and thrown into space by the explosive force as the material for the formation of the next generation of galaxies. If the remaining core does not exceed 3.2 times the mass of the sun, a neutron star will be formed.

Let's take a microscopic look at how neutron stars are formed. Atoms consist of nuclei and extranuclear electrons. The nucleus consists of neutrons and protons. From the structural diagram of helium atom, most of the volume of an atom is occupied by extranuclear electrons. When the pressure is high enough, the electron will be compressed to the lowest energy level, and then the electron degeneracy pressure will appear very large. If the electron degeneracy pressure can defying gravity collapse, it will form a white dwarf. When the mass of star debris is greater than 1.44 solar masses (Chandraseka limit), electrons will be pressed into the nucleus, and electrons will form neutrons with protons, which is a neutron star. At this time, the force against gravity collapse is neutron degenerate pressure. Like electron degeneracy, it is the force provided by Pauli exclusion principle. If the mass of the remnant stellar core is greater than 3.2 solar masses (Oppenheimer limit), nothing can resist gravity, and it will collapse into a black hole.

Neutron star is a very dense celestial body, its density is between 80 million tons and 2 billion tons/cubic centimeter, almost beside the nucleus. The great gravity makes the escape speed of its surface reach 50% of the speed of light. This means that a 70 kg person will release 200 million tons of TNT equivalent energy when he hits it. Four times the power of the largest hydrogen bomb. However, not all neutron stars are made up of neutrons. Due to the short half-life of the free neutron, the outer neutron decays continuously, releasing electrons, protons and neutrinos. The middle layer consists of free neutrons; The pressure at the core may have crushed the nucleus and formed a quark core, but this is only a guess. A neutron star looks like a giant nucleus, but it is different from a nucleus that is polymerized by strong interaction. It is bound by gravity. So it is still a celestial body. Of course, don't try to take out the neutron star material alone: degeneracy pressure will make the nucleus spread rapidly, and free neutrons will also decay rapidly. In the Big Bang, these neutron star materials will return to normal atoms.

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