stars. life cycle of star h8jz6fu5d1a h8jz6fu5d1a
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Stars
Life cycle of starhttp://www.youtube.com/watch?v=H8Jz6FU5D1A
http://aspire.cosmic-ray.org/labs/star_life/starlife_proto.html
1. Nebula = cold, dark cloud of dust and gas [mostly H]
gravity pulls particles, to clump together
Accretion: accumulating more mass
Clumps increase in size [accretion]pressure and temperature increases [due to KE
of particles]
2. Protostar when forces are in equilibrium : gravity collapses particles together, high temperature/pressure
pushes particles apart.
At equilibrium Gas pressure = gravity
If protostar too small, becomes brown dwarf, never a real star.
4. STAR If enough mass, critical temperature protostar core begins
to fuse H into He :star is born.
The star is stable while the gravitation
pulling the star together is balanced
by the internal pressure pushing it apart.
During lifetime, stars fuse Hydrogen into Helium
and then fuse helium into Carbon.
Massive stars can fuse carbon into heavier elements.
3. Main sequence
90% of stars spend majority of life on the Main Sequence
On the main sequence, hydrogen is fused into helium
H is fused into He..
Main sequence is a grouping of stars by size, color, luminosity
We compare other stars to the brightness [luminosity ] of the Sun:
Temperature determines the color of a star
Temperature Color
30,000 - 60,000 K Blue stars
10,000 - 30,000 K Blue-white stars
7,500 - 10,000 K White stars
6,000 - 7,500 K Yellow-white stars
5,000 - 6,000 K Yellow stars (like the Sun)
3,500 - 5,000K Yellow-orange stars
< 3,500 K Red stars
Mass-luminosity relationship for Main Sequence Stars
L = Lo[M/Mo]3.5
Lo = luminosity of SunMo = mass of Sun
The Herzsprung-Russell Diagram H-R diagram
shows relationship of luminosity, temperature, size
[ H-R diagram]
Note the scales are log scales, not linear.
Mo is the mass of the Sun
Low mass stars: 0.5Mo
medium mass stars: 0.5Mo – 3Mo
massive stars: >3 Mo
Larger, hotter stars burn out very fast - in a few million years.
Smaller, cooler stars burn slowly for billions of years
The Sun is a medium yellow star.
The surface temperature is about 6000K
The Sun has a life expectancy of about 10 billion years
Try the interactive star lab: http://aspire.cosmic-ray.org/labs/star_life/starlife_sequence.html
Wh
After becoming red giantlow mass stars [mass of Sun] shrink
into white dwarfs.
Radius is close to radius of Earth.
Medium mass stars [ 1.4 to 3 Mo] expand into Red Giants , collapse
and then explode into a supernova
Finally becomes a neutron star
[about the size of Manhattan]
Massive stars collapse and begin to fuse carbon.They explode as supernova and the core is
crushed into a black hole .
After all H is fused, star leaves the main sequence.
Pressure increases, stars expand enormously and cool.
Small stars expands and sheds outer layers
Medium stars expand into red giants
After about 100,000 years the protostar has drawn in enough dust and gas to become a
star.
When core temperature reaches 10 million degrees, H begins to fuse into He,
releasing energy [heat]
Most stars are Main Sequence Stars
When core H has all fused to He,
About 1 million Earth’s fit in the Sun
http://www.youtube.com/watch?v=g4iD-9GSW-0
Sun compared to largest star
http://www.youtube.com/watch?v=Bcz4vGvoxQA
Black hole swallows a starhttp://www.youtube.com/watch?v=O3Z5AS3TTS4
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