1. Characteristics of Stars

2. Elements in Stars 99% Hydrogen (H) and Helium (He)
1-2% Oxygen, Carbon, Nitrogen, Calcium
Sun is 70% Hydrogen and 28% Helium
Produce energy (heat and light) by fusing hydrogen atoms to make helium

3. Physical Properties of Stars
Star Color is dependant on surface temperature.
Hot stars = Blue or White, ~30,000 K
Cool stars = Red or Orange, ~3,000 K
The Sun = Orange or Yellow, ~5,500 K

4. Absolute Magnitude
Stars actual brightness  distance of 32.6 light years from the sun
Depends on size and temperature of the star.
What would the brightest star look like?

6. At this size, a dwarf star is too small to see

7. D C E B A Low Temp High Temp
1. Each letter represents a star, what type is each and what color is each? 2. What 2 things does this diagram tell you about stars? D C E B A
Low Temp
High Temp

8. Answers… A – White Dwarf, White B – Main Sequence, Yellow
C – Main Sequence, Blue
D – Super Giant, Red
E – Giant, Red
Surface Temperature & Absolute Magnitude (Brightness)

9. Origin of Stars Nebulae (huge clouds of hydrogen gas and dust)
Diffuse Nebula: visible due to the light provided by close stars
Dark Nebula: blocking other stars

10. Formation of Protostars
Something outside the nebula triggers the gravity between gasses and dust
A supernova shockwave
Nebula contract
As the nebula contracts, spots in it start to glow with heat  protostar

11. Formation of Main Sequence Stars
Protostar continues to contract  Fusion begins
IMPORTANT: STARS ARE ALWAYS TRYING TO COLLAPSE DUE TO THEIR OWN GRAVITY
It keeps collapsing until the star’s released energy equals the force of gravity
It is now a Main Sequence Star

12. Formation of Giants/Supergiants
Hydrogen decreases  energy of fusion no longer balances the force of gravity
Core of the star contracts and get hotter
Increases the rate of fusion for the remaining Hydrogen
The increased energy causes the outer layers to expand  Giant/Supergiant

14. Formation of Dwarfs No fuel  Star collapses due to gravity
Squeezes the nuclei together very tightly dwarf
The can glow for billions of years as they cool

15. Non Massive Star Life Cycle
Nebula

16. Massive Star Life Cycle: Supernova
Fusion stops in massive stars  forms super dense core with extremely strong gravity
The gravity causes the star to collapse past the dwarf stage
Collapse puts intense pressure on the core
Star explodes violently and half its mass is blown away  supernova

17. Supernova Before and After

18. Neutron stars Leftover half of supernova that doesn’t blow up
Its gravity is so strong that all of the atoms particles (p+, n, e-) are crushed together, leaving only neutrons
Neutron stars may be 10km wide, are a trillion times as dense as the sun.

19. Black Holes
If the star is massive enough, its gravity causes it to collapse past the neutron phase into a tiny volume, but humongous density/gravity  Black Hole
The gravity is so great that not even light can escape

20. How do we know they exist?
Strong X-Ray emissions from the Cygnus constellation
When something gets sucked into a black hole, its atoms get ripped apart and it emits x-rays

21. Galaxies and Universe

22. Solar system - the sun, orbiting planets, asteroids, meteors, and comets
The sun is 1 star in a galaxy, which is a group of millions or billions of stars held together by gravity
Our galaxy is in the universe, which contains all the planets, stars, solar systems, and galaxies

23. The Milky Way 100 billion stars Every visible star
It is 1 of 17 nearby galaxies that make up the Local Group

24. Milky Way Facts Diameter: 140,000 light years
Width: 20,000 light years
Sun 23,000 light years from the center
That’s Us!

25. Sprial Galaxies
Spiral Galaxies central nucleus, arms coming off the nucleus.

26. Barred Spiral Galaxies

27. Elliptical Galaxies
Range from spherical to lens shaped most common

28. Irregular Galaxies
Smaller, fainter, and less common, no pattern

29. Big Bang Theory Universe began as a dense sphere of hydrogen.
13.7 billion years ago it exploded, forming a gigantic, expanding cloud of gas and dust
Evidence
Red Shift
Microwave Radiation