Download The Lives of Stars

The Lives of Stars
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Evolution of Stars
Newton’s Laws of Gravitation state:
All masses attract each other
This force gets stronger the closer the objects
are together
Gravity is constantly at work
It is the force that helps create and build stars, but
ultimately causes them to die
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Nebulae
Astronomers speculate that stars form from gas
and dust clouds called nebulae
Gravity pulls the material togethe
Accumulating gas increases temperature
At 10,000,000 degrees nuclear fusion begins (transformation of
hydrogen into helium)
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Main Sequence Stars
Fusion begins
Starts to consume hydrogen
Helium begins to accumulate in the core
Interior begins to heat up increasing
temperature and pressure
Forces are balanced by gravitational pull
The time a star takes remains stable depends on
mass
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Low Mass Star (Red Dwarf)
Consume Hydrogen slowly ~100 billion
yrs
Lose mass becoming a white dwarf
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Intermediate Mass Stars(like sun)
Consume Hydrogen faster over about 10
billion yrs
When Hydrogen used up core begins to
collapse
Temperature increases
Outer layer begins to expand 10 – 100 times its
size
Outer layer is cooler so it looks red (Red Giant)
Sun will eventually become this reaching Mars
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Intermediate Mass Stars(like sun)
Stellar winds peel off outer
layer revealing inner layer
Planetary Nebula
Eventually disperses and star
becomes white dwarf
Over time core cools and they
become a black dwarf (dark
cinder)
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Massive Stars
Consume Hydrogen quickly
Core gets so hot Helium fuses into heavier
elements
Swells into Supergiant
Burn core in ~7 billion years
Helium burning stage ~ 500,000 yrs
Silicon is transformed into iron in 1 day
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Supernova
Massive stars
After iron core stage no fusion to counteract
gravity
Core collapses
Massive shock wave bursts from the star’s surface
(Supernova)
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Neutron Stars
After supernova two
possible fates
If core is 1.4 – 3 Solar masses
Gravity collapses remnants into
10 – 20 km diameter (Neutron
Star)
Located because they give off
pulsars
Greater than 3 solar masses
Form Black Holes
Objects so compact and dense
not even light can escape
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Formation of Stars
People thought space (inter-stellar medium) was
empty
Stellar winds
Planetary nebulae
Supernovas
All fill space with large quantities of gas and dust
All essential for making new stars
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Formation of the Solar System
The theory of how stars and planets are
formed is called the solar nebula theory
Scientists suggest the sun is 5 billion yrs old
9 planets orbiting around it are 4.6 billion yrs old
Catastrophic Theory
Star collided with sun
Debris scattered formed planets
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Formation of Solar System
Smallest planets closest to sun were
blasted with radiation
Didn’t have enough gravity to hold on to their
hot atmospheres
Became rocky inner planet (M,V,E,Ma)
Planets farther out kept their gas
Became the gas giants (J,S,U,N,P)
Throughout history loose rocks and dust
pounded planets (evidence in craters on
Mercury and the Moon)
Mostly cleared up now except for some
debris accumulated around planets
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Hunt for Extra-Solar Planets
Planets products of star formation so they
should be fairly common
There are 100 recorded examples of
young stars
There are about a dozen extra-solar
planets (planets that orbit stars other than
the sun)
A planet 2.5 times the size of Jupiter obits a
star near the Big Dipper