What LC Knows About Neutron Stars
with no trouble taken for presentation
Neutron stars are a type of star. Stars are humongous things the exist in space. The nearest star to the planet Earth is the sun. After that is Alpha Centauri, which is 4 lightyears away.
Neutron stars are small, old stars. Probably the last stage in those particular stars' "lives." Although some may acquire more mass and become black holes (from sources such as other stars in binary systems). And I suppose they must run out of energy eventually and become something like a black dwarf. But probably smaller than what I would think of as a black dwarf.
Neutron stars are what's left over when a massive star (over the limit of about 1.4 solar masses, which I think is the Chandrasekhar limit?) supernovas and does not have enough mass left (one source says 2 or 3 solar masses) to become a black hole. If the original star is under the limit it will become a white dwarf instead, which is supported against gravity by degenerate-ness of electrons. Anyway, neutron stars have been collapsed a lot by gravity, but are supported by the exclusion principle (which means they are degenerate, because to be degenerate matter must be dense enough to be affected by the exclusion principle) acting on neutrons. Neutron stars are really small, like 10 km in radius, compared to white dwarves, which are Earth-sized, or other stars, which are really really big. Neutron stars are really dense. I think they are made of neutronium, but I got that from Star Trek: The Next Generation. White dwarves are so dense that a teaspoonful of white-dwarf-material would weight tons. Neutron stars are like hundreds of times denser than that.
Neutron stars are made of neutrons because all the protons and electrons inside got squished together. It is possibly like an equilibrium in there becaus they tend to come apart again, but there are a few protons and electrons there to squish together too. I think producing neutrons like this produces antineutrinos, too. (Or was it neutrinos? I forget.)
Neutron stars spin, because they were spinning previously. They spin really fast now that they are neutron stars, because they got small without losing angular momentum. They spin much faster because the angular momentum of a sphere depends on the square of the radius or some such. Must look up that formula. But the neutron star in the Cygnus supernova-remnant spins maybe 30 times per second? Something like that. Must look up that number.
There is a widely held idea that neutron stars have crusts like planets such as Earth (complete with mountains, but they are tiny because the gravity is so strong) and are superfluid (zero viscosity) inside. This is supported by some idea that vortices in the superfluid account for glitches in the rotational period of the neutron star. The vortices were supposed to move outward toward the crust and get stuck, then cause the glitches by unsticking. I don't have any idea what that's about. Someone said neutron stars are big neutron crystals. But he seems to be outnumbered by the superfluid people. Maybe he is just outdated. Plus I don't trust him that much.
Neutron stars are a lot like pulsars because it seems that most if not all pulsars are actually neutron stars. They have strong electromagnetic fields because they got smaller. How exactly that works, I don't know. Maybe it is like the gravity and it is stronger because you can get closer to the center. Anyway, these electromagnetic fields accelerate charged particles, which creates photons, and apparently there is variation in the strength of this effect, because as the neutron star turns the strong part of the beam turns too, like a lighthouse. People didn't notice this at first because neutron stars turn really fast, so the signals the radio telescopes received were ignored because they were screened out with the static because they pulsed so fast. Then someone wanted to study static (which is apparently rapid variation caused by solar wind and such) and he noticed pulsars. One of them is in the center of the Cygnus supernova remnant, which is right where a neutron star might be expected to be.
Oh yeah, the exclusion principle keeps being worded as "two particles can't have almost the same location and almost the same velocity at the same time." But apparently this really means there is some constant that specifies how close these both combined can be. It's a quantum mechanics thing. Anyway, this exclusion principle comes into effect at great densities where the particles are forced into close enough proximity. It makes them repel each other. This provides pressure that can counteract gravitational pressure and create white dwarves when it acts on electrons and neutron stars when it acts on neutrons.