beginning of stars and low mass star life cycle

what are the stages that all stars are expected to go through?

nebula → protostar → main sequence star

how does a nebula turn into a protostar?

the gravitational attraction within the nebula pulls the particles closer together until a hot ball of gas forms

what happens during the stage of being a protostar?

the density of the protostar increases as the particles are pulled closer together

this results in more frequent collisions between the particles, which causes the temperature to increase

when does a protostar turn into a star?

if the temperature gets high enough, nuclear fusion occurs to turn hydrogen nuclei into helium nuclei, and turns into a star

the nuclear fusion reactions release heat and light energy which keeps the core of the star hot

for most of a star’s life, it’ll remain stable in this stage

how are stars held together?

stars are held together by a balance of the inward and outward forces, keeping the forces in equilibrium

gravity acts as an attractive force inwards, but pressure acts outwards as a result of the energy released by nuclear fusion, so the star expands

what does the lifecycle of a star depend on?

its size

what stages do stars a similar mass to the sun (lower mass) go through?

red giant → planetary nebula → white dwarf → black dwarf

how does the main sequence star turn into a red giant?

hydrogen begins to run out, and the outward force becomes less than the inward force due to gravity, so the star collapses inwards

the collapse of the star causes the sun’s temperature to increase, and this causes helium nuclei to fuse together to create heavier elements, and the star expands to become a red giant

how does a red giant turn into a white dwarf?

the red giant runs out of helium nuclei to fuse, and the star becomes unstable, collapsing under its own gravity to become a white dwarf

what turns a white dwarf into a black dwarf?

the white dwarf will be cooling down, as it is no longer carrying out fusion and the energy it emits will decrease until it stops producing, really any energy, and forms a black dwarf