Notes

* a star is born
they are born, they go through a life cycle, and then they die
* a nebula is a large cloud of gas and dust that's spread out in an immense volume
* gravity is can pull some of the gas and dust in a nebula together

Nebula theory
the sun and planets formed from a rotating disk of dust and gases
as the speed of rotation increased, the center of the disk began to flatten out
Matter became more concentrated in this center, where the sun eventually formed

Protostar
* Protostar is when the cloud pulled together and forms a protostar, which is the earliest stage of a stars life
* A star is born when the nebula contracts gas and dust and becomes so hot and dense that nuclear fusion stars

The Life span of a star
* the mass of a star determines how long it will live
* a low-mass main-sequence star uses up fuel slowly and eventually becomes a white dwarf.
* A low-mass star like the Sun takes billions of years to use up their nuclear fuel

Cycle in which a small-mas star dies
* As they run out of fuel, they become red giants first.
* Eventually, the outer parts grow larger and drift into space forming a glowing cloud of gas called "planetary nebula"
* The blue-white core of the star left cools and becomes a white dwarf

High-mass stars
* High-mass stars quickly evolve into brilliant supergiants
* When a supergiant runs out of fuel, it explodes into a supernova. The remains either become a neutron star or a black hole
Neutron star
* After a supergiant explodes, some of the materials left from the star become a neutron star
* They are smaller and denser than white dwarfs
Black hole
* After a very massive star dies in a supernova explosion, the gravity of this mass is so strong that the gas becomes dense and pact.
* A black hole is an object with gravity so strong, not even light can escape it