1. Stars and the Sun
a star is a ball of hot plasma (like a gas with an electrical charge)
90% of the matter in the universe is plasma
it is not “on fire”
it does not “burn” like a fire does

2. Why is a star hot? Nuclear fusion
4 hydrogen atoms are pushed together to make 1 helium atom
left over particles released as energy
the opposite of what happens in nuclear power plants (fission) where atoms are split up

3. Anatomy of a star Has layers just as the Earth does
Core: center where fusion takes place (15 mil K)
Radiative zone: energy moves out from center
Convective zone: energy rises and sinks, some escapes

4. Anatomy of a star Photosphere: light we see comes from here
Has atmosphere just as the Earth does
Chromosphere: first layer of atmosphere … is pink!
Corona: extends out into space

5. Brightness of a star depends on: called the magnitude (2 kinds)
how big the star is (bigger = brighter)
how far from Earth it is (closer = brighter)
how hot it is (hotter = brighter)
called the magnitude (2 kinds)

6. Brightness of a star Kinds of brightness:
Luminosity: measure of the amount of energy given off. Measured as compared to the Sun (1), logarithmic 102, 104
Apparent magnitude: as seen from Earth, lower (including negative) is brighter!
Absolute magnitude: if all stars were same distance from Earth, lower (including negative) is brighter!

7. Spectrum the visible light waves that a star gives off or absorbs
Different for each element…like a fingerprint
can tell us:
what star is made of how fast moving
how far away it is how fast spinning
if its moving to/away

8. Spectrum

9. Star color Related to temperature
Stars give off all wavelengths of light, but usually more of one wavelength (color)
Red = ~ 3,500K Orange = ~ 5,000K
Yellow = ~ 6,000K White = ~ 10,000K
Blue = ~ 15,000K +

10. HR Diagram
Plots brightness and temperature

11. HR Diagram Groups: Grouped by spectrum:
Main sequence: diagonal line, 90% of stars
White dwarfs: hot, but small, lower left
Red giants/supergiants: cool, but big, upper right
Blue Giants: hot and big, upper left
Grouped by spectrum:
O B A F G K M
Oh, Be A Fine Girl (Guy) Kiss Me

12. Stars Life Cycle
Goes through different stages, depending on mass: more mass = bigger and hotter
All stars start as a cloud of gas and dust (nebula)
Condenses and eventually fusion starts, but very cold star (protostar) and usually can’t be seen in nebula

13. Nebulae and protostars

14. Stars like the Sun
Become Main Sequence stars next as gas and dust continue to condense and the nebula disappears
Fuse H  He for about 10 billion years
Runs out of H, core shrinks, outer layers cool and expand (red giant)
Big enough to swallow first 3 planets
Uses He other elements for about 10 million years

15. Stars like the Sun
Runs out of He, core shrinks, outer layers float into space (planetary nebula)
Core left over, small and hot (white dwarf)
Eventually fuses up to carbon, ends as small cold ball of carbon (black dwarf)

16. Stars like the Sun

17. Stars bigger than the Sun
8x or more massive
Nebula  protostar
A star with much more mass than the Sun will be bigger and brighter (blue giant) but not last as long
Then it will get bigger and cooler (red supergaint)
It can fuse elements up to Iron (Fe #26)

18. Stars bigger than the Sun
When core is made of iron, it can’t condense anymore. The great gravity pulls the outer layers in quickly and they hit the iron core and rebound, exploding in a supernova
In that explosion elements heavier than iron are formed

19. Stars bigger than the Sun
The core is usually left over.
If the core isless than 3 times the mass of the Sun, it will become a neutron star … something so dense that electrons are pushed into the nucleus and cancel out protons and make all neutrons! Some give out regular pulses of radio waves (pulsar).
If the core is 3x or more massive than the Sun it collapses again into a black hole…so dense that not even light escapes!

20. Stars bigger than the Sun

21. Relative star sizes

22. Relative star sizes

23. Galaxies Collections of millions or billions of stars
Also interstellar matter … gas and dust
Grouped together in clusters ours is called the Local Group
Clusters form superclusters and so on

24. Galaxies 3 basic shapes: Spiral Elliptical Irregular
Central bulge with spiral arms
Older stars towards center, younger ones on outside
Sometimes a bar instead of a bulge … barred spiral
Elliptical
Oval or round, no arms
Mostly older star , little interstellar matter
Irregular
No regular shape
No pattern to kinds of stars or amount of interstellar matter

25. Spiral Galaxies

26. Elliptical Galaxies

27. Irregular Galaxies

28. Galaxies Milky Way Quasar
Most likely a spiral galaxy…strip of stars is the spiral arm
Hard to tell without leaving it
Quasar
Most distance and radiant object i space
Very young galaxy
Change over time … as stars change and run into each other

29. Colliding Galaxies