Stars
Life cycle of star
http://www.youtube.com/watch?v=
H8Jz6FU5D1A
http://aspire.cosmicray.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 Sun
Mo = 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.cosmicray.org/labs/star_life/starlife_seque
nce.html
Wh
After becoming red giant
low 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
HR diagrams
http://www.youtube.com/watch?v=
Kqe6F-Qf9Tk
Black hole swallows a star
http://www.youtube.com/watch?v=
O3Z5AS3TTS4