Neutron stars are the last remotely normal matter objects that exist before we get to black holes.
Black holes, those things you cannot check out of once you go past the event horizon. Black holes, those things that can gobble up stars for a snack. We can’t see them directly, just the surrounding maelstrom of hot stuff caught in their gravity and racing around at relativistic speeds. The Event Horizon Telescope, a planet-wide array of radio telescopes has imaged a black hole’s shadow and it looks menacing.
Mass determines how a star evolves once it forms. The simple formula is: More Mass = Faster Evolution. Our Sun is considered a lowish mass star, a yellow dwarf star, and will hum along for about 4 billion years more before any major evolutionary changes take place. Those changes will however occur in a rapid succession, over just millions of years, resulting in our Sun becoming a white dwarf, a white-hot core remnant of compressed electrons. A process called electron degeneracy pressure prevents gravity from crushing the core further. It’s a force that prevents electrons from sharing the exact same state. Kind of like trying to park two cars in the exact same spot in a parking space. It will not likely be fusing any elements to produce energy, just cooling down over a period of maybe a trillion years.
OK, that’s a “normal” star. Neutron stars are not normal and come from stars many times more massive than the Sun. So do black holes. The difference is primarily with the original star’s mass, but there are a few qualifiers, so some overlap exists. They both come from the evolutionary end of very massive stars, that is, a supernova. The difference is how massive the star’s resulting core is after the supernova. That’s right, the end result, neutron star or black hole, is the star’s core remnant after it blows up.
If the core remnant comes in at around 1.5 – 3 solar masses, it will likely become a neutron star. A process called neutron degeneracy pressure, like electron degeneracy, keeps gravity from crushing the core any further. Neutron stars are so dense a teaspoon of one would weigh as much as Mount Everest.
If the core remnant’s mass is greater than around 3 solar masses, neutron degeneracy pressure can’t keep gravity from crushing it and whoa, nothing. Well, not nothing, but it is fantastically small and has infinite density to boot! It defies close inspection with current technology, so we just call it a black hole. Can’t see them, they do not emit light, any light within can’t get out. It’s beyond current physics.
My question, why aren’t white dwarfs called electron stars? Or maybe neutron stars should be called blue dwarfs?
What’s in the Sky?
October 20; dawn; east: Mercury rises – use binoculars
October 21; pre-dawn; south-southwest: Orionid meteor shower peaks with a nearly Full Moon-boo!