Star Death (Life Cycle of Stars)

Step 1 Main Sequence Star

Outward pressure caused by energy released by nuclear fusion is perfectly balanced by inward pressure caused by gravity → allows for a long stable period ~ million or billions of years (the stage our Sun is at)

Step 2 Star Contracts

At some point the star will start to run out of hydrogen → star unable to do any more nuclear fusion → inward pressure (gravity) takes over + contracts the star into a small ball until it's hot and dense enough that nuclear fusion can start up again → this will cause it to expand again → however, instead of just forming helium, the nuclear fusion will form heavier elements (all elements up to iron on period table)

Step 3 Star expands again

How much the star expands depends on how big the initial star was( the initial mass it had):

1) if it was a small/medium star (e.g. our Sun)→ form a Red Giant

2) if it was a really big star → form a Red Super Giant

Red Giant ending

1) After short time Red Giant becomes unstable → expels outer layers of dust and gas → leaves behind a hot, dense, solid core that doesn’t do any nuclear fusion → White Dwarf → as it gives off lots of light so it appears white + is relatively small

2) White Dwarf gets cooler and darker as it emits all of its energy → Black Dwarf as it no longer has enough energy to emit light

Red Super Giant ending

Red Super Giants start to shine brightly again as they undergo even more nuclear fusion → after several cycles of expansion & contraction they explode into a supernova → supernovas form elements even heavier than iron that get ejected all across the universe

2) What happens next again depends on how big the star was:

A) very big → supernova will condense into a very dense core (neutron star)

B) absolutely massive → if neutron star collapses in on itself + become a black hole → it is called a black hole because it is so dense that their gravity is able to pull in any gravity that passes nearby → they appear as empty spaces/tiny holes in the universe where no light is ever emitted