1. The Life and Death of Stars
Notes #7

2. Structure of the Universe
Our universe contains hundreds of billions of galaxies
Each galaxy contains hundreds of billions of stars

3. Our galaxy is called the “Milky Way”
It is a spiral galaxy made of 400 billion stars

4. Our Solar System is located out in one of the spiraling arms of the Milky Way
center US

5. The Milky Way 100,000 light years across Our Solar System
1 light year is how far light travels in one year.
Since light travels at 671 million miles per hour this equals 5,878,499,810,000 miles in one year.
So, our Galaxy is 587,849,981,000,000,000 miles across. It’s BIG !!!!!

6. You can see the Milky Way on a clear, Moonless night

7. Star Formation Where did all of these stars come from?
A star forms from a cloud of interstellar gas and dust called a nebula.

8. Star Formation
This cloud collapses on itself from gravity into a protostar.
When it becomes hot enough for nuclear fusion, it is officially a star

9. Nuclear Fusion Hydrogen atoms fuse into helium atoms.
This releases energy that powers stars.
Proton
Beta particles
Hydrogen is fused to
Become Helium

10. The Lifecycle of Stars
When stars are born, they become main sequence stars where they spend 90% of their life.
Main sequence stars come in a variety of sizes, colors, temperatures, and luminosities.

11. Our Sun Luminosity = 1 Temperature = 57000 K or 60000 C Color = yellow
Size = little less then average
Age = 4.6 byo

12. The Lifecycle of Stars
The smaller the main sequence star, the dimmer, redder and cooler it is.
The bigger the star, the hotter, bluer and brighter it is.

13. Size Determines Life and Death
Stars like our Sun live about 10 billion years until they use up their hydrogen fuel.
Smaller stars use H slower, so they live longer.
They will expand into giant stars and then quietly become white dwarfs where they eventually burn out.

14. LIFE CYCLE OF A STAR LIKE OUR SUN

15. Size Determines Life and Death
Larger main sequence stars use H faster so they die quicker.
They will become supergiants and then die in a supernova explosion.
This can make a black hole or neutron star.

16. LIFE CYCLE OF A MASSIVE STAR

17. Chandra X-ray Observatory image of Cassiopeia A, a 300-year-old supernova remnant.

18. SN 1994D, a type 1a supernova in the NGC 4526 galaxy (bright spot on the lower left).

19. Absolute vs. Relative Magnitude
Absolute magnitude is a measure of the energy that a star is releasing.
Relative/Apparent magnitude is how bright it looks to us. Determined by size and distance.
A bright star may appear dim if it is extremely far away.
A dim star may appear bright if it is close.

20. The Big Dipper-which stars are the brightest and dimmest?