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Life and Death
Of
A Star
Color
H-R diagram
lifecycle
Star color
• A star’s color is directly related to its
temperature
• Blue – hottest
• White – hot
• Yellow – medium
• Red – Cool
Hertzsprung - Russell
• Stars are organized by luminosity and
temperature
• As a “normal” sized star goes through its
life it cools and grows dimmer
• these are know as main sequence stars
Hertzsprung - Russell
• Larger stars are more luminous and
appear at the top of the chart as Giants or
Super Giants.
• Main sources stars that have collapsed in
on them self become low luminosity White
Dwarfs
Birth of a star
• Begins as a cloud of gas and dust –
Nebula
• Then condense until areas become more
dense and begin to glow – protostar
• eventuality a protostar becomes so hot
that fusion begins – now a star
• The amount of mass determines whether
the star is a main sequence star or a giant
A Star’s Beginning
• All stars begin when the fusion of H begins
– 2 H become one He (blue into yellow stars)
• The force of Fusion
pushes out on the star
• The force of Gravity
pulls in on the star
– Creating equilibrium
Death of a main sequence star
• Once there is enough He it begins to fuse
and form carbon and oxygen
• C and O build up in the core
– But Temperature never gets hot enough for these
to fuse
• When the hydrogen is used up the balance is
gone star gently collapses in on its self
• Leaving a halo of gas and dust
– planetary nebula (where new stars form)
• And a dense hot core
– white dwarf
Death of a Super Giant Star
• In a giant the C and O get hot enough to fuse to
heavier metals (everything up to Fe)
– (Red Giants and Super Giants)
• Iron is the final element formed
– Fe nuclei does not release energy it absorbers it
• So a giant’s core quickly collapses in on its self
sending a shockwave that blasts the outer layers
of the star into space – Supernova
– Creating a dusting of all the elements over a large
area
Remnants of a massive Giant Star
• neutron star – a neutron’s stars gravity is
so high that electrons are forced into the
protons making them all neutrons
• When a neutron star first forms it spins
giving off bursts of radio waves – Pulsar
• If a star is big enough (15 solar mass) the
gravitational force would become so great
that light could not escape – black hole
Life of a star