Neutron Stars

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Neutron stars exist because of the death of stars

Stars exist because of a fragile balance. Millions of billions of trillions of tons of whole plasma are being pulled in by gravity and squeezed together. Material squeeze together with so much force that nuclei fuse together. Hydrogen fuses to helium, which releases energy which pushes against gravity. Stars are stable because of this balance.

Eventually helium will be exhausted. For medium size stars like our sun, it will go through a giant phase where they burn helium into oxygen and carbon before they turn into a white dwarf. But with stars many times the mass of our sun, different things happen when the helium is exhausted. At some point, the balance of radiation and pressure tips, and gravity wins squeezing the start tighter than before. The core burns hotter and faster while the outer layer expands 100 of times and starts fusing heavier elements. Helium fuses into neon in centuries, neon into oxygen in a year, oxygen into silicon in months, and silicon to iron in a day, then death.

Iron has no energy to give out and can't fuse. It's nuclear ash. So the balance stops, and the core is crushed by the weight of the star above it. Electrons and protons fuse into neutrons because of the huge pressure, that squeeze together as an atomic nuclei. An iron ball the size of the earth is compressed into a ball of pure nuclear matter the size of the matter. But not only the core squeezes, but the outer layers of the star are pulled inwards as well at 25% the speed of light, to bounce on the core, create a shock wave and catapults parts of the star in all directions.

This is a supernova explosion and it outshines entire galaxies. What remains is a Neutron Star, which's mass is 1M times that of the earth, compressed in an object of 25Km wide. It is so dense that the mass of the entire population of the earth would would fit in 1cm3 of it. It's like mount everest in a cup of coffee or a billion tons in a sugar cube.

A neutron star's gravity is the strongest after black holes, if it was a bit stronger then it would be a black hole. Life is bent around it so you could see the front and parts of the back.

Their surfaces reach 1M degrees celcius compared to 6000 degrees for our sun.

They have an atmosphere, a crust, and a liquid core.

The outermost layer is extremely hard, made of iron nuclei leftover from the supernova (made of protons and electrons), with a sea of electrons flowing through them.

Going deeper, gravity is stronger, getting nuclei closer and closer together and we see less protons and most have turned into neutrons. We then reach a point where the nuclei are squeezed so tight together that they start to touch, protons and neutrons start rearranging and form long cylinders or sheets of long nuclei with millions of neutrons and protons shaped like spaghetti and lasagna. Scientists call this nuclear pasta. Nuclear pasta is so dense that it might be the strongest material in the universe. It's unbreakable. Lumps of pasta inside a neutron star can form mountains a couple cm high but as massive as the Himalayas.

Beneath the pasta is the core. We are not sure what the properties of matter are when they are squeezed this hard together. Protons and neutrons might dissolve into a sea of quarks known as the Quark-Gluon Plasma. Some of those quarks might turn into strange quarks making a sort of strange matter with properties so extreme. Or they simply stay neutrons and protons. No one knows for sure.

When neutron stars first collapse, they start spinning very fast (many times a second). These create pulsars because their magnetic field creates a beam of radio waves which passes every time they spin. The radio pulsars are the best known type of pulsars (over 2000 we know of in the Milky Way). They have a magnetic field of 100B Tesla right after they're born (strongest magnetic field in the universe) compared to 0.00005 Tesla of earth. They are called Magnetars until they calm down a little.

The best kind of neutron stars are friends with other neutron stars. They radiate energy as gravitational waves, ripples in space time, their orbits decay until they collide and kill each other in a Killanova that spews out most of their guards. When they do, conditions become so extreme, that for a moment, heavy nuclei are made again. It's not fusion putting nuclei together this time, but heavy neutron rich matter falling apart and reassembling. Most heavy elements in the universe probably originate from this (gold, Uranium, Platinum, Holmium, Bismuth, Iridium, and dozens more). When two neutron stars collapse together they form a black hole. Not only do stars need to die once to create elements, they need to die twice. Over millions of years, these elements were mixed back into the galaxy, but some of them end up in a cloud that gravity pulls together to form planets and stars (solar nebula), restarting the cycle. The solar system is an example, and the remains of the neutron stars that came before us are all around us. Everything in our world is made by elements from neutron stars in the past.

PS: There are 100 billion billion earth like planets in the habitable zone of sun-like stars in the observable universe.