nuclear reactions produce
energy to keep the star hot
planets
formed
when
smaller
amounts of
dust and gas
clump
gravity pulls gas and dust together
As the gas falls
together, it gets hot. A
star forms when it is
hot enough for nuclear
reactions to start. This
releases energy, and
keeps the star hot.
some stable stars
change in their lifetime
to form other types of
stars
E.g sun is a stable star
forms many different types
red giant
white dwarf
neutron stars
black holes
during a stars main sequence
period of life it is stable
forces are balanced
outward pressure
from expanding
hot gases is
balanced by the
force of the stars
gravity
our sun is currently in its
stable phase
stages of lifecycle
determined by size
life cycle of a star:
stars the same size as our sun
follow the left hand path
main
sequence>
red
giant>white
dwarf> black
dwarf
stars much bigger than our sun
follow the right hand path
main sequence>super red
giant>supernova>neutron
star or blackhole
nuclear fusion in a star
stars are so hot nuclear
fusion can take place
stars have enough hydrogen to
maintain energy output for millions of
years
used in order to release energy
hydrogen nuclei fuse
together to form helium
nuclei
as the star runs
out of hydrogen
other fusion
reactions take
place and start to
form other
element nuclei
heavier elements than
hydrogen (<Fe) are
formed
elements >Fe are
formed in
supernovas
heavy elements are found in the sun
and planets, suggesting that they
were formed from the remains of
earlier stars that exploded as
supernovas