- Around massive objects, Newtonâs theory of gravity isnât right.
- Massive objects bend 3D space, so nearby objects bend into a 4th dimension: time.
- Stars form from gas clouds being collapsed by gravity.
- Stars of all different sizes and hotness are created.
- Spectral Types: OBAFGKMLTY (TY = failed stars)
- Only Boring Astronomers Find Gratification Knowing Mnemonics Like This â Yeah!
- Stars in same spectral type have same spectra.
- Most stars are along the main sequence: dim and cold and small to bright and hot and big.
- Sun spots are spots where the electrical field is stronger and the sun canât convect.
- Gas comes up and doesnât go back down and cools.
- Nuclear fusion: the sun takes protons, smashes them together, and ends up with helium.
- 4 protons â helium and light
- Protons must be heated to 10 million Kelvin to be smashed together
- Therefore stars must be at least 10 million Kelvin
- Nuclear fusion defines a star on the main sequence
- Eventually stars run out of hydrogen
- Big bright stars burn out fast
- Big stars: 100,000 - 1,000,000 years
- Our sun: 10-12 billion years
- Smallest stars: trillions of years
- Stars donât collapse because of pressure outwards from energy.
- When it runs out of hydrogen, it collapses, then gets really hot because itâs small, then expands to a red giant
- Red giant (in center) is now hot enough to fuze 3 heliums to get a carbon.
- You can keep fuzing to get other elements.
- If the star is 8x the mass of the sun, it collapses and explodes, creating a supernova.
- This is how we got all of our current elements â they exploded into space via a supernova
- Whatâs left is a âneutron starâ, which is the mass of the sun but the size of a city.
- If the star is 25x the sunâs mass, it becomes a black hole (has mass but no size).