First, you have a star. It lives its life, fusing hydrogen to helium due to the extreme pressure and heat due to gravitational pressure. Later in a star's life, after the hydrogen has all been fused into helium. Nuclear fusion is the process in which two atoms of lighter elements come so close together (from the sun's massive gravitational pull) that the Nuclear force (aka 'strong force') holding an atom's nucleus together pulls the two atoms together forming a new atom with a higher atomic number.
Back to the star though--Hydrogen has all become fused to helium, a heavier element. This makes the star burn hotter and denser. Then, helium fuses into a heavier element (carbon). During this time period, a star will swell up until it becomes so vast, it either explodes or implodes (when this time comes in our sun's life, it is theororized that the sun will become so big it'll swallow the first 3 planets of our solor system).
Now that the star has fused lots and lots of different elements like so:
it ends up with an ashen iron core. Iron is unusual in that it is extremely stable and resistant to fusion. The temperature of an iron core can reach 3 billion degrees. When the iron core reaches a critical mass, it collapses, violently, into a supernova explosion.Yes, but I don't care about supernovas :D--It's scenario B I'm interested in. Here is a nice way of putting it:
If you didn't understand that, then basically know that with that high of pressure, protons and electrons get smashed together so tightly that they make neutrons. OMFG! T3h neutron star!astro.umd.edu wrote:the basic idea is that when the central part of the star fuses its way to iron, it can't go any farther because at low pressures iron 56 has the highest binding energy per nucleon of any element, so fusion or fission of iron 56 requires an energy input. Thus, the iron core just accumulates until it gets to about 1.4 solar masses (the "Chandrasekhar mass"), at which point the electron degeneracy pressure that had been supporting it against gravity gives up the ghost and collapses inward.
At the very high pressures involved in this collapse, it is energetically favorable to combine protons and electrons to form neutrons plus neutrinos. The neutrinos escape after scattering a bit and helping the supernova happen, and the neutrons settle down to become a neutron star, with neutron degeneracy managing to oppose gravity. Since the supernova rate is around 1 per 30 years, and because most supernovae probably make neutron stars instead of black holes, in the 10 billion year lifetime of the galaxy there have probably been 10^8 to 10^9 neutron stars formed. One other way, maybe, of forming neutron stars is to have a white dwarf accrete enough mass to push over the Chandrasekhar mass, causing a collapse.
OMFG, I'm so tired now, I know this sounds stupid, but I'll finish writing this post tomorrow :D
