1. The Sun, Formation of Elements, the Big Bang, and Black Holes
Stars
The Sun, Formation of Elements, the Big Bang, and Black Holes

2. Stars
Mass of plasma held together by its own gravity and creating light and heat using nuclear fusion
Make up galaxies
Always there – don’t see them in daytime b/c sun is so bright, atmospheric skylight overwhelms star light.

3. Formation Most of Space = really empty
1 million times more empty than we can make on Earth
Gas and Dust attract other gas and dust using gravity
Nebula – Cloud of dust and gas
More gas = more mass, more gravity, attracts more gas
Makes a Protostar – forming star, huge cloud of gas and dust
Cloud pulls together due to gravity, nuclear fusion occurs and makes a star

4. Lifetime
Large stars = lots of gravity -> lots of nuclear reactions -> very bright -> burn out quickly
Smaller stars = less bright, last longer
Sun = avg. star, lasts around 10 billion years
Has been around 5 billion years so halfway through its life.

5. Lifecycle of a star

6. Classification Determine what stars are made of by energy they emit.
X-rays, light waves, radio waves
Type of waves indicate what atoms are in star.

7. Classification: H-R Diagram
Also classified by surface temp and brightness using the H-R Diagram

8. Our Sun Typical star – medium size, low mass
Yellow star half way through main sequence stage
75% Hydrogen (H), 25% Helium (He)
Similar to billions of other stars

9. Nuclear Fusion
Nuclear fusion – small atoms combine into larger atoms, releasing huge amts. of energy
Requires enormous heat and pressure – found in core of stars due to mass and gravity
In sun, H fuses to form He, releasing energy as heat and light
Changes more than 600 million tons of H into He each sec.
When sun runs out of H in 5 billion years, it will start fusing He turning it into a red giant
Nuclear fusion = start of star, how star makes energy

10. Nuclear Fusion H -> He

11. Formation of Elements
All elements larger than H and He were formed by nuclear fusion in the core of stars
At the end of the star life cycle, the star explodes in a Nova – star explosion
Large elements are then released as star dust.
Star dust comes together to form planets, rocks, etc.
All oxygen, gold, iron, carbon, etc. formed in the core of stars by nuclear fusion
So we’re all made of star dust!!!
You’re a star, you’re a big, bright, shiny star!!!

12. Periodic Table of Elements

13. Big Bang - Evidence
Red shift of distant galaxies indicates they’re all moving away from us
So if we move them in “rewind” they get all get closer together
Eventually, all converge at single point around 14.6 billion years ago – universe is 14.6 b.y. old
Cosmic Background Radiation – very slight amt. of heat in deep space (3 K)
Heat likely came from big bang and is slowly cooling

14. Big Bang 14.6 billion years ago, everything was in a single point
No matter, just pure energy
Point expanded, energy cooled, and matter was formed as Hydrogen and Helium
H and He pulled together by gravity formed first generation of stars.

15. Black Holes
Black hole – remains of giant star that has collapsed on itself
So dense, such great gravity that nothing can escape, not even light
Only form at end of stars life for REALLY big stars
Once fusion is done, gravity is too great, has nothing left to fuse/burn so collapses on itself

16. Sun as Black hole Our sun cannot be a black hole – too small
But if it could, it would shrink from 1,400,000 km across to infinitely small while keeping same mass
Light within 3 km of center would be trapped
Would Earth be sucked in?

17. Sun as Black Hole
No. Mass of the sun (and gravity) would be the same, so our orbit would be unchanged.
Would only affect things that got to where the center of the sun is now
And it’d be really dark/cold
We know they exist b/c we can see things react to their gravity, but can’t see them.
NOT the same as a wormhole - won’t take you to another dimension/place. Will just crush you into a single point.