Download - Star's Life Cycle
EVOLUTION AND LIFE CYCLE OF STARS
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STARS Life Cycles: • A Star goes through a life cycle just like
humans would.
Birth
Life Death
Birth of a star
A shockwave causes nebula gas and dust to collapse due to
gravity.
As the cloud collapses
and shrinks due to
gravity, it compresses the gas and
starts to heat up inside
(compression creates
heat).
It gets so hot that nuclear fusion starts
inside the center of the cloud
(a protostar forms).
Birth of a Star
The high heat and
temperature from the fusion
reaction increases the
forces of outward
pressure and the protostar
grows and starts to expand.
Eventually, a balance between gravity wanting to collapse the
protostar and the heat and
pressure wanting to expand the
protostar is met.
A star is born and
burns happily.
Shockwave
Gravity compress
es star
Heats up fusion begins,
pressure balances
with gravity.
Hydrogen is
burning and
balancing out the
compression from gravity.
REVIEW…
This balance between gravity and heat and pressure from fusion must be kept in order for a star to live peacefully.
If a star does not burn enough hydrogen, then gravity will overcome it and it will start to collapse in on itself again.If a star makes too much energy, it will expand too much, thus shutting down the fusion reactions, ultimately causing the star to collapse again until fusion starts back up
A star will continue to live happily as long as it balances internal pressure and gravity.
Fusion for a star is like FOOD for us, With it we are sustained and can live. Without it, we die.
HAPPY LIFE – Main Sequence
Implication
More Mass
• The more massive a star, the harder it has to try to overcome the force of gravity working to collapse it.
More Fusion
• The only way a star can overcome the collapsing force of gravity, is through the expanding heat and pressure of fusion.
More Hydrogen
• The more massive stars, need to burn more hydrogen than less massive stars.
Star live happy until it uses up its food: Hydrogen
Stars live happy until they run out
of food. It can no longer
overcome gravity and
starts to compress
again.
Bigger stars need more
food to overcome
gravity and thus use up there food faster (die earlier).
A dying star changes from
a main sequence start to
another type of star.
Depending on the mass of the star.
What happens when a star eats all its food? When it’s hydrogen inside its core runs out?
THE STAR EXPANDSAnd is now
burning Helium
BECOMES A RED GIANT or SUPER GIANT
DEATH• At this time, gravity and heat and pressure are
unbalanced. • The star begins to collapse as it cannot
overcome gravity without fusion.• What happens after this point depends on the
MASS of the star.
Medium – Low Mass Stars (like the sun).
The stars core
continues to
collapse
The star collapses so much that
the enormous amount of
heat produced
causes leftover
hydrogen in a cloud
outside the core and He in the core
to burn.
This burning causes
the outer atmosphere of the star to be
wisped off into space
leaving just the
stars core behind.
This core is called a
white dwarf. White dwarfs are the
same size as earth but way
more dense.
High Mass Stars
Hydrogen runs out in
the core much more
quickly because
of its high
mass, collapsin
g the core.
It collapses so much
that the inside heats
up much more than
inside a mediu
m mass star.
High mass stars are
more massive, fusion of elements heavier
than H and He take place,
causing the star to
expand rapidly into a super
giant star.
Eventually, the
star runs
out of fuel in
the core
causing fusion
to stop.
The star collapses
in on itself and
then explodes outward forming
a supernov
a
After the explosion however,
the core of the star remain
and becomes either a
black hole or a
neutron star
depending on just
how massive it
is.
Supernova
From a Supernova… now what?1.4 to 3 times the mass of the sun
Core will collapse to about the size of a
small city.
Pressure from neutrons in the core stop the core from collapsing further.
Neutron Star
Greater than 3.0 the mass of the sun.
Core will collapse to about the size of a
small city.
Pressure from neutrons in the core
CANNOT stop the core from collapsing.
Core shrinks down to a point called a
singularity.
Black Hole is formed.
Neutron Stars• Small• Extremely Dense - teaspoon weighs a mountain• Stupendous surface gravity• Rotate 1000 times per second (pulsar)
neutron star
marshmallow
3-megaton explosion
Black Holes• Massively dense core of a dead star
compressed to a speck.• There is an imaginary sphere around the black
hole called an event horizon.• Anything that goes into the event horizon can not escape its stupendous gravity.
Black HolesIf Sun became black hole (not possible)…orbits of planets would be engulfed.event horizon
BH
Total Distortion (“Spaghettification”)
Gas, stars falling towards BH are tidally distorted even outside the event horizon.
Distortion heats up stuff to millions of degrees and emit X-Rays strongly.
Feeding BH’s should be very bright X-Rays.
You can find a BH in space in looking for normal star and a binary companion emitting X-Rays (The star will be at least 3 times the mass of the SUN).