Stellar Evolution

A. “LIFE CYCLE” OF STARS Of course stars aren’t really alive, this is just for comparison

1. A star begins in a nebula when gas & dust contract

2. A protostar forms when gas & dust start to combine in nuclear fusion

3. Stars with less mass exist longer than stars with more mass Like a Toyota Camry vs. a Tractor-Trailer Big Rig, smaller means more efficient!

4. When mass starts to run out, nuclear fusion slows

5. Star’s gravity weakens & it expands, becoming a red giant or supergiant

6. When a Red Giant runs out of fuel: a. the outer parts drift out to space & leave the core behind (“a white dwarf”) Comparable to Earth in size

b. when the white dwarf stops glowing, it is a dead “black dwarf”

a. after the supernova, some material drifts off 7. A dying Supergiant can suddenly explode in a “supernova” a. after the supernova, some material drifts off to space, becoming another nebula.

b. material left behind becomes a small, dense neutron star

can escape its gravity and it becomes a black hole c. after the most-massive stars go supernova, the material left behind grows so dense that not even light can escape its gravity and it becomes a black hole ← But it isn’t really a hole, see?

B. Our Sun Our sun is about 5 billion years old, and it should last about another 5 billion years.

2. It is medium-hot, and medium-bright

3. Eventually, our sun will become a white dwarf

4. Our sun is a star on a spiral arm in the Milky Way Galaxy

Our sun - and our entire solar system - revolve around the center of the Milky Way

b. There is a black hole at the center of the Milky Way… but don’t worry, it won’t gobble us up! It acts like an anchor for the galaxy to swirl around.

C. Black Holes This “singularity” - or remnant of a dead star might be as tiny as a single atom, or as large as 20 of our suns put together

2. The Event Horizon - the area around the singularity that is affected by its gravity

b. The gravity is so great within the event horizon, that not even light can escape

3. Crossing the Event Horizon - If a person jumped in, the gravitational pull on his feet would be so strong, that his body would start to stretch

b. His feet would stretch more as they moved in, and then his legs would start to stretch

c. This “spaghettification” would continue until...

d. The force of the singularity’s gravity ripped him apart and/or crushed him completely :-(