STARS

I. Stellar EvolutionI. Stellar Evolution

The Life Cycles of StarsDr. 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 SequenceStay a stable size because gravity

counteracts H�He fusion.

http://physics.uwyo.edu/~stark/outreach/StarLives/life+death/fusion.gif

H�He

A Balancing Act

2. Throughout its life, these two forces determine the stages of 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.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

He�CHe�C

H�He

http://physics.ship.edu/~mrc/pfs/108/node3.htm

http://www.physics.hku.hk/~nature/CD/regular_e/lectures/images/chap15/red_size.jpg

Planetary Nebulae

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.

E. The Fate of a Red Giant1. 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

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,

G. The Fate of a Supergiant

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 – Instead of releasing E, it uses E

This is where the

elements come elements come

from!

The massive E absorbed causes the Supergiant to

www.theage.com

the Supergiant to explode in a Supernova!

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

OROR

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

Supernovae compress

gas and dust which lie

between the stars.

This compression starts

The Cycle Continues

This compression starts

the collapse of gas and

dust to form new stars.

The Life Cycles of StarsDr. 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)are)

RED �ORANGE�YELLOW�WHITE�BLUECOOLEST …………………………………………………………………………………………….HOTTEST

+15-----------------------------�-15DIMMEST………………………………………………………………….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 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. Spectroscope-device used to tell the composition of a starstar

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. Elliptical1. 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. Irregular1. 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 D. The North Star= Polaris. We see it all year.

E. Circumpolar stars- circle Polaris and can also be seen all year