Transcript Chapter 26.3, Life Cycles of Stars

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How Stars Form: -The space around stars
contains gas/dust
A nebula is a large cloud of dust/gas, some
nebulas glow lit by other stars and some are
cold and dark that block the light from
distant stars behind it
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Stars are created by gravity.
Gravity pulls the nebula’s dust/gas into a
denser cloud, as it contracts it heats up
A contracting cloud of dust with enough mass
to form a star is called a proto-star
A star is formed when a contracting cloud of
dust/gas becomes so dense and hot that
nuclear fusion begins
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Spend about 90% of their lives in main
sequence (converting hydrogen to helium)
A star’s mass determines the star’s place on
the main sequence and how long it will stay
there
The amount of gas/dust when the star forms
determines the mass of the star
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High mass stars become the brightest/bluest,
about 300,000 times brighter than sun
Because they are bigger and burn so brightly,
they only last for a few million years
A yellow star like our sun will remain stable
for 10 billion years
A red sequence star may stay in sequence for
more than 100 billion years (Formed from
small nebulas, 1/10 the sun’s mass)
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When a star runs out of fuel gravity starts to
compress the core and causes it to shrink
Then the star will begin to fuse helium into
carbon/oxygen/and other heavier elements
Once all fuel is gone it causes the star to die
and turn into a white dwarf, neutron star, or
black hole
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Can be 8 times as massive as the sun will
eventually turn into white dwarfs
The dying star is surrounded by a glowing cloud
of gas called a planetary nebula (Because the 1st
ones found looked like planets viewed through a
small telescope)
Once it blows off most of its mass, only its hot
core remains (Size of Earth but still about the
same mass as before)
Once it cools its called a black dwarf (Takes 20
billion years so the universe has not been around
long enough for this to occur)
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More than 8 times the mass of the sun, grow
into super-giants creating new elements , the
heaviest being iron
Dies quickly because it consumes its fuel very
rapidly
Once the star runs out of fuel the star
collapses and explodes as a supernova
(Becomes brighter than an entire galaxy)
Produces elements heavier than iron
-Rare Earth Elements
-Uranium, Platinum, Gold, Etc
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The heavier elements in our solar system,
including the atoms in your body, came from
a supernova that occurred in our galaxy
billions of years ago
As the supernova spews material into space,
its core continues to collapse
If the remaining core has a mass less than 3
times the sun’s mass, it will become a
neutron star (This star is dense,
electrons/protons are crushed together by
the enormous gravity to form neutrons)
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Neutron stars are much smaller and denser
than white dwarfs
A spoonful of a neutron star would weigh
nearly a billion tons on Earth
Can spin hundreds of times a second
If a neutron star gives off strong pulses of
radio waves it is called a Pulsar
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If a star’s core after a supernova explosion is
more than 3 times the sun’s mass, gravity
causes the collapse beyond the neutron star
stage
The pull of gravity increases and the speed
required to escape the star’s core reaches the
speed of light
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Beyond this point, nothing can escape and a
black hole is formed
A black hole is an object whose surface
gravity is so great that not even
electromagnetic waves, traveling at the speed
of light, can escape from it