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Question: Describe the Doppler Effect.

Answer: … … …

Turn In:-p. 534 CYU #3-7, 9-Expansion of Space

Turn In:-p. 534 CYU #3-7, 9-Expansion of Space

The Life Cycle of a Star

What do cars have to do with stars?

Cars and Stars

Size For cars: curb weight For stars: intrinsic brightness

Energy Produced For cars: horsepower For stars: temperature/ color

How long it takes to burn all its fuel For cars: mileage- how long it takes to burn 1 tank

of gas For stars: hydrogen gas

ECity Mileage vs Weight

0

5

10

15

20

25

30

35

40

45

50

0 1000 2000 3000 4000 5000 6000 7000

Curb Weight

Cit

y M

ilea

ge

Series1

INVERSE RELATIONSHIP

Horsepower vs Curb Weight

0

100

200

300

400

500

600

0 1000 2000 3000 4000 5000 6000 7000

Curb Weight

Ho

rsep

ow

er

Series1

DIRECT RELATIONSHIP

2500 5000 10000 20000 40000

Temperature (K)

What type of relationship is this?

Direct

Which car graph is this most similar to?

Horsepower vs Curb Weight

Stellar Evolution

Stars exist because of gravity. Mass attracts mass.

A nebula (cloud of gas and dust) provides the starting material.

Stellar Evolution

As the cloud is squeezed, the temperature rises, it ignites and a star is born.

A star is a ball of gases balanced between gravity’s contraction (pulling in) and nuclear explosions (pushing out).

Nuclear Explosions

Protostar

Gravity continues to cause contraction of star

Core is heated more than the surface

Nuclear fusion begins

Huge amounts of energy are released

Main Sequence Star

Balanced between gravity’s contraction and gas pressure’s expansion

Massive stars burn fast (several million yrs.)

Small stars burn slow (hundreds of billions)

Average stars burn for about 10 billion yrs. The sun is an average sized star

90% of a star’s life is spent as Main Seq.

The Sun

2500 5000 10000 20000 40000

Temperature (K)

Why do we call them “Main Sequence Stars?”

Most of the stars fall on the “best-fit line” on this graph, which we call the main sequence

• same graph you just saw, but with one change (look at the x-axis)

• x-axis goes from largest to smallest

• Traditional way that the H-R Diagram is displayed

• Draw and label the main sequence in your notes

H-R Diagram

Red Giant (old age)

All hydrogen fuel has been used

Core contracts and heats up

Heat causes star to expand up to 1000 times larger

Star cools as it expands

Fate of average mass stars

Supergiant (old age)

Fate of large mass stars

Core contracts and heats up

Heat causes star to expand

Star cools as it expands

Generates all the elements on the periodic table (up to iron)

Size Comparison

Burnout and DeathSmall and Average StarsSmall stars: Main Sequence White Dwarf Black Dwarf

Medium stars:Main Sequence Red Giant White Dwarf

Black Dwarf

Burnout and DeathVery Massive Stars

Supernova: an explosion of the star that leaves a nebula

Supernovas

Supernovae are one of the most energetic explosions in nature, making them like a 1028 megaton bomb (i.e., a few octillion nuclear warheads).

These two photographs are of the same part of the sky.

This photo was taken in 1987 during the supernova explosion of SN 1987A.

This photo was taken before the Supernova explosion

After a Supernova, the core of the star…

Neutron Star: very small and very dense

Black Holes: gravity is so large that even light cannot escape

Black Holes

http://antwrp.gsfc.nasa.gov/apod/astropix.html