1) PROTOSTAR - simply the
force of gravity causing gas
and dust to spiral in together
2) MAIN SEQUENCE STAR - gravitational
energy is converted into heat energy
causing temperature to rise when its hot
enough hydrogen nuclei undergo nuclear
fusion to form helium nuclei giving out
masses of heat and light giving birth to a
star, smaller clumps of dust and gas may
form planets that orbit the star
3) MAIN SEQUENCE STAR - the star enters a long and
stable period where the heat created by the nuclear
fusion creates an outward pressure to balance the
gravitational force pulling everything inwards the stars
energy output is then maintained for millions of years
due to the collosal amount of hydrogen it consumes the
MAIN SEQUENCE STAR period lasts around several
billion years (the sun is halfway through this period)
eventually the hydrogen runs out and
heavier elements (e.g iron) are made by
nuclear fusion of helium the star then
swells into a RED GIANT if its a small star
or RED SUPER GIANT if its a big star it
becomes red due to the surface cooling
RED GIANT - a small/medium star then
becomes unstable and ejects its outer layer
of dust and gas as a PLANETARY NEBULA
WHITE DWARF - leaving behind
a hot, dense and solid core
BLACK DWARF - occurs after the
white dwarf has cooled small
black dwarfs eventually dissapear
However big stars undergo more fusion and glow
brightly again they expand and contract several
times forming elements as heavy as iron in various
nuclear reactions eventually it explodes as a
SUPERNOVA forming elements heavier than iron
and ejecting them into the universe to form new
planets and stars.
the exploding supernova
throws its outer layers of dust
+ gas into space leaving a very
dense core called a NEUTRON
STAR if the star is big enough
it will become a BLACK HOLE