Download Life Cycle of a Star Notes

LIFE CYCLE OF A STAR
Stars are born in nebulae. These are huge clouds of dust and
gas which collapse under gravitational forces to form
protostars. These young stars undergo further collapse,
forming main sequence stars.
Stars expand as they grow old. As the core runs out of
hydrogen and then helium, the core contacts and the outer
layers expand, cool, and become less bright. This is a red
giant or a red super giant (depending on the initial mass of the
star).
It will eventually collapse and explode. Its fate is determined by
the original mass of the star; it will become a brown dwarf (or
black dwarf), neutron star, or black hole.
HT
Stars glow because of a nuclear fusion
reaction
whereby
hydrogen
fuses
together to form heavier elements such
as helium and release energy.
If enough matter is left behind, this may
be so dense, and its gravitational field so
strong that nothing can escape from it,
not even light or other forms of
electromagnetic radiation. It is then called
a black hole. We cannot see black holes
but we can sometimes observe their effects on their
surroundings, for example, the X-rays emitted when gases
from a nearby star spiral into a black hole.
Mr Powell
Gases & Rocks float in space (nebula)
The gases contract and rub together for about 40
million years to form a protostar (baby star)
Gravity pulls them together to form a star which can attract
planets. This main sequence star lives for about 10 billion
years. The Suns nuclear reaction balances the gravity of the
gases.
Then the forces become unbalanced and the sun
expands to become a red super giant or red giant
Sun like stars
become red giants
Stars with a mass more
than 1.5x of our sun
become red super giants
They shrink to form a
planetary nebula then
white dwarf. A cool star
mostly carbon
Supernova or explosion of
gases
Over time can form a
brown dwarf the
temperature is not enough
for fusion to occur inside
the core
If the mass of the star is no
more than 3x that of our Sun it
forms a Neutron star
If the mass of the star is over 3x that
of our Sun if forms a Black hole
Mr Powell
FLOW CHART
Sun-like Stars (Mass under 1.5 times the mass of the Sun) -->
Red Giant --> Planetary Nebula -->White Dwarf --> Brown Dwarf
Huge Stars (Mass between 1.5 to 3 times the mass of the Sun) -->
Red Super Giant --> Supernova --> Neutron Star
Giant Stars (Mass over 3 times the mass of the Sun) --> Red
Super Giant --> Supernova --> Black Hole
Mr Powell