Question of the Day 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

E INVERSE RELATIONSHIP

DIRECT RELATIONSHIP

Temperature (K) Brightness 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

Temperature (K) Brightness 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 Death Small and Average Stars Small stars: Main Sequence White Dwarf Black Dwarf Medium stars: Main Sequence Red Giant White Dwarf Black Dwarf

Burnout and Death Very 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