1	Stellar Evolution
2	Dude, Where’s my Star? People have been looking for explanations both of what and where stars are for ages. But the Notion that Stars even evolve is really new. Early theories, all thought of stars as objects manipulated by gods Apollo By the middle ages people saw stars as a manifestation of gods might Ptolemy and the “Almagest” Stars are holes which let light shine through
3	So, how do stars evolve anyhoo? By the 19^th century (thanks to Laplace) people now conceived stars as DYNAMIC! This meant that stars could evolve But How? Well, it is easy to think of their evolution as a three part process Stellar babies– what astro goons call “Pre main sequence” 9-5 stars– They work, they heat, they smash atoms at 10 million K Arthur Miller’s “Death of a star”
4	Pre-Main Sequence, Schmequence When solar system forms mass almost evenly spread out A Big Cloud Gravitational Trigger needed Thanks to angular momentum, we end up with a lovely disk The disk eventually becomes the planets But what happens in the center?
5	Star Cores: GRTNE¹ As the cloud collapses the center gets denser and denser At some point it becomes so dense that it can hinder its own light from escaping. (This is called being optically dense) Optically dense stars heats up faster than the NASDAQ before a Fed meeting Because they are hotter, they also have more radiation pressure Hydrostatic Equilibrium Quite volatile during this stage and often have conniption fits
6	Before the Mid-life crisis: The H-R Diagram So after stars settle down from their “Youthful indiscretions” they become predictable or in astronomy language, “Boring” H-R Diagrams graph the stars temperature to how bright it it is. They are helpful devices for figuring out what is going on in the star for two reasons: H-R diagrams can also show how old a star is and … H-R diagrams show how big a star is But how exactly?
7	H-R Diagram Continued Well, the closer you get upper left hand corner of the graph the larger and younger stars become (they are the sumo wrestlers of the star world) While the closer you get to the lower right hand corner of the graph….
8	Yet More H - R The more they would look more like this dude Our sun is right smack in the middle of this graph and has neither age nor size to boast about,but what it lacks in character, it makes up for in stability
9	Hooray for the stable sun! This stability is good news for life. To put it gently, if the sun wasn’t so stable Mr. Kitty would be burned by huge fire balls from space, and bombarded by high intensity gamma or “Chemo” rays giving poor Mr. Kitty kitty leukemia . In short, Mr. Kitty would become Kitty Crisp! But the nuclear fuel which balances the suns collapse is slowly used up over a long period. So eventually all the fuel is gone.. What will happen after this occurs?
10	Death Stars At the end of their lives, stars become drastically unstable and evolve in a myriad of directions based on how much they weigh. We will focus on the deaths of stars of three different masses: Sun’s Death Deaths of stars a lot heavier than the sun, a.k.a. Neutron Stars The Death of Huge stars like Betelgeuse which will end up as Black Holes Let’s Focus on the Sun First
11	Our Sun’s Death
12	Red Giants, Better than Jolly Green Once the the fuel is used up in our sun, it will shrink New Type of Nuclear Fusion is Triggered Because this new type of fusion only happens closer to the surface of the star, it inflates the entire star to MONSTRO sizes. These stars are called Red Giants Pop Quiz Time: What does GRTNE stand for (35 pts)
13	Red Giant Act II The Sun will eventually become a Red Giant, and in the process gobble up Mercury and Venus. Red Giants use fuel really quickly So, within a few million years all the new fuel will be used up. What will happen next to the sun?
14	Hi-Ho! White Dwarfs Here we come After all nuclear reactions stop, the gravitational attraction will still try to contract the sun Will anything stop this madness? Luckily,in the early days of Quantum Physics Wolfgang Pauli noticed that more than two electrons can’t exist in the same place at the same time. You can think of this as saying that electrons hate sharing their room with more than one other electron Lesson Learned: Electrons are bad roommates
15	White Dwarfs: The saga continues So, when a star collapses it eventually tries to force more than two electrons together This causes the electrons to get feisty They try vigorously to get away from one another Thus they move so fast that they create a pressure which can hold up the gravitational collapse This pressure is known in Astro-babble as “Electron Degeneracy Pressure.” This will allow the sun to become stable again Eventually it will cool off and become a Black Dwarf But What happens to stars a little bigger than the sun?
16	The Death of a Neutron Forming Star
17	Neutron Stars² So for stars a little larger than those that become white dwarfs, the electron degeneracy pressure isn’t quite enough to stop Gravity. But Neutrons also obey the Pauli Exclusion Principle As the star heats up it increases electron speed. When the core reaches nuclear densities, they have relativistic speeds and the core becomes a giant particle smasher These electrons turn the protons into neutrons, which then display a “Neutron Degeneracy Pressure” Freakish Magnetic Fields But what happens when papa stars like Betelgeuse collapse?
18	Betelgeuse’s Death
19	BeetleJuice’s Death
20	Black Holes For super duper massive stars, nothing can stop the collapse Eventually it reaches a point where even light (which is the Michael Johnson of the Physics world) can’t escape from its gravitational pull. This is the so called Schwartzchild Radius.
21	Black Holes 2.0^® The center of the black hole has been traditionally defined as a point of infinite density called a singularity. Not possible to communicate with inside Recently, it has been suggested that singularities don’t exist at all, instead the center is a tiny vibrating super string, which means that at the end of their lives Jumbo stars end up as single particles Wow! It doesn’t get any cooler than that. Fortunately, because this presentation is….
22	OVER