STARS
I. Stellar Evolution
The Life
Cycles
of
Stars
Dr. Jim Lochner, NASA/GSFC
A. Nebula- cloud of
gas and dust
B. Protostar- spinning disk
C. Main Sequence
1. When the protostar reaches 15 million C,
nuclear fusion begins. (H He) and
enormous amounts of E is released.
Main Sequence
1. When E begins to be released,
a star is “born”
Main Sequence
Stay a stable size because gravity
counteracts HHe fusion.
HHe
http://physics.uwyo.edu/~stark/outreach/StarLives/life
+death/fusion.gif
A Balancing Act
2. Throughout its life,
these two forces
determine the stages of
a star’s life.
D. Red Giant/Supergiant
1. When H gets low, gravity causes the star
to shrink & heat up.
2. Increased heat & pressure cause He to
fuse to C.
3. The excess E released makes the star
expand to a red giant or a supergiant.
10x bigger than the sun
100x bigger than the sun
HeC
HHe
http://physics.ship.edu/~mrc/pfs/108/node3.htm
http://www.physics.hku.hk/~nature/CD/regular_e/lectures/imag
es/chap15/red_size.jpg
He supplies get low, and the red giant begins to
shrink in a series of contractions, giving off a
planetary nebula and leaving only a white, hot
center.
Planetary Nebulae
E. The Fate of a Red Giant
1. The white center is called a white dwarf.
*It is the size of the Earth with the mass
of the sun.
* It weighs a ton per teaspoon.
http://abyss.uoregon.edu
2. When the white dwarf “burns out” it
becomes a black dwarf.
http://library.thinkquest.org
http://www.physics.hku.hk/~nature/CD/regular_e/lectures/chap15.html
F. Nova
1. Sometimes a white dwarf has an
explosion called a nova before becoming
a black dwarf.
ttp://www.astropix.com
G. The Fate of a Supergiant
1. After He gets low in a supergiant, the
core collapses again until it becomes hot
enough to fuse C into Mg or O
2. Through a combination of processes,
successively heavier elements are
formed and burned.
4. Fe is the most
stable element
and cannot be
fused further.
– Instead of
releasing E, it
uses E
This is where the
elements come
from!
The massive E
absorbed causes
the Supergiant to
explode in a
Supernova!
www.theage.com
Supernova
H. What’s Left After the Supernova?
1. Neutron Star (If mass of core < 5 x Sun)
• Under collapse, protons and electrons
combine to form neutrons.
• 10 Km across
OR
2. Black Hole (If mass of core > 5 x Solar)
Neutron stars can have 2 beams of
light coming off of them called pulsars.
www.sciencemus
eum.org.uk
The Cycle Continues
Supernovae compress
gas and dust which lie
between the stars.
This compression starts
the collapse of gas and
dust to form new stars.
The Life
Cycles
of
Stars
Dr. Jim Lochner, NASA/GSFC
Twinkle, Twinkle, Little Star ...
How I Wonder What You Are ...
• Stars have
• Different colors
Which indicate different temperatures
• The hotter a star is, the faster it burns
its life away.
II. The H-R Diagram
A. Interpreting an H-R Diagram
1. An H-R diagram compares the surface
temperature of stars with their absolute
magnitude (how bright the stars actually
are)
RED ORANGEYELLOWWHITEBLUE
COOLEST …………………………………………………………………………………………….HOTTEST
+15------------------------------15
DIMMEST………………………………………………………………….BRIGHTEST
H-R Diagram
2. For most stars, as the surface temp increases,
brightness increases
3. Main band of stars in the diagram are called
main sequence stars
4. The cool bright stars in the upper right are
red giants that appear bright because they
are large
5. White dwarfs in the lower left are hot but
appear dim since they are small
B. Analyzing Stars
1. Spectroscopedevice used to tell
the composition of a
star
2. Spectrum- The
reading a
spectroscope gives
you.
www.upscale.utoronto.ca/GeneralInt
erest/Harrison/Spectra/spectra.gif
3. You can tell how a
star moves by
observing its
spectrum.
4. Red shift in a
spectrum means a
star is moving away.
5. Blue shift means a
star is moving
closer.
www.upscale.utoronto.ca/GeneralInt
erest/Harrison/Spectra/spectra.gif
III. 3 Types of GALAXIES
spiral
elliptical
irregular
A. Basic Galaxy Info
1. Avg 100,000 light-years in diameter
2. There are at least 1 billion galaxies
3. They are classified based on shape
B. Spiral
1. Has a bright nucleus of stars.
2. Flattened arms spiral around the nucleus.
3. The Milky Way is a spiral galaxy.
C. Elliptical
1. Shape ranges from nearly spherical to a
flattened disk.
2. Very bright in center and has no spiral
arms.
3. Usually older than other types & have
little dust & gas.
D. Irregular
1. Have no particular shape.
2. Small and faint.
3. Stars are unevenly distributed
IV. Basic Star Info.
A. Constellation- group of stars
B. Big Dipper= Ursa major
C. Little Dipper= Ursa minor
D. The North Star= Polaris. We see it all
year.
E. Circumpolar stars- circle Polaris and can
also be seen all year