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Life Cycle of a Star

The changes that a star goes through is
determined by how much mass the star has.
Two Types of Life Cycles:
Average Star- a star with relatively low mass
Massive Star- a star with relatively high mass
Life Cycle of Stars
http://www.seasky.org/cosmic/sky7a01.html
Stellar Nebula


All stars begin in a
cloud of gas and dust
called a stellar
NEBULA.
Gravity will cause the
nebula to contract.
The nebula will break
into smaller pieces.
These pieces will
eventually form stars.
Protostars

Protostar – after a
few million years,
the gas forms into a
disk with a small
dense core

~1500K
The Life of an Average Star


An Average Star (low mass
star) is condensed in a nebula
and begins a nuclear reaction
that causes hydrogen to form
helium, releasing energy in the
form of heat and light.
A low mass star will stay in this
MAIN SEQUENCE phase for a
long time, until it begins to use
up all of it’s hydrogen.
Red Giant


Towards the end of it’s
MAIN SEQUENCE
phase, a star begins to
burn all of its hydrogen.
The outer layers will
collapse, become
heated by the core and
expand out forming a
red giant.
Planetary Nebula


The star begins to
quickly blow off its
layers forming a cloud
around the star called a
planetary nebula.
The star in the center of
the nebula is very hot
but not very bright.
White Dwarf


When a star has
burned all it’s fuel it will
collapse under the
pressure of gravity.
The white dwarf that
forms is very small and
dense.
Star with Similar Mass of the Sun
Life of a Massive Star p. 388&404
Stellar Nebula


All stars begin in a
cloud of gas and dust
called a stellar
NEBULA.
Gravity will cause the
nebula to contract.
The nebula will break
into smaller pieces.
These pieces will
eventually form stars.
Life of a Massive Star


Stars with more mass
than the sun (high
mass stars) burn their
hydrogen faster than
low mass stars, so their
MAIN SEQUENCE
phase is much shorter.
These stars burn hotter
and brighter than low
mass stars.
Red Supergiant


When the high mass star
burns off it’s hydrogen its
outer layers begin to
expand rapidly.
Temperatures at the core
are much higher than a
red giant. Nuclear fusion
causes elements to
combine into an iron core
at amazing speeds.
Supernova


The iron core collapses on it’s self under the intense
gravity at very high speeds.
The energy released is called SUPERNOVA.
Neutron Star or Black Hole


After the incredible release of
energy from the SUPERNOVA
a dense core (1 trillion times
denser than a white dwarf) is
all that remains of the Massive
Star.
If the mass is too dense it will
continue to collapse on itself
forming a black hole. The
gravitational pull of a black hole
is so great, light can not
escape.