1. Life Cycle of Stars
Mr. Weaver

2. Birth of a Star Nebula- A cloud of gas and dust where stars are born.
Composed mostly of Hydrogen, with a little bit of Helium

3. Horsehead Nebula

4. Hourglass Nebula

5. Carina Nebula

6. Pillars of Creation
Eagle Nebula

7. Birth of a Star
Dust and gas pulled together by gravity, forming a disk. Center gets hotter as it gets compacted
Massive jets of matter shoot out perpendicular to the disk
When core reaches 15 million K, fusion starts and the star is born
Leftover matter in disk forms planets

8. Formation of Star and Planets

10. Main Sequence
Hydrogen converted to Helium in core through Nuclear Fusion
Star is made up almost entirely of Hydrogen and Helium
Our Sun is in the Main Sequence
90% of a Star’s total lifetime

12. Death Depends on Size
Up to 12 Solar Masses: Red Giant, then White Dwarf
12-25 Solar Masses: Supernova/Neutron Star
25+ Solar Masses: Supernova/Black Hole

13. Sun Sized Stars
As Hydrogen runs out, core collapses inwards and gets hotter
Outer layers of Star expand outward
Star swells into a Red Giant

14. Our Sun as a Red Giant in ~5 Billion Years

15. Sun Sized (continued)
As Hydrogen runs out, Helium starts fusing into heavier elements
When fuel runs out, the Red Dwarf sheds its outer layers, forming a Planetary Nebula
Remaining Core is called a White Dwarf

16. Planetary Nebula
White Dwarf

17. For Much Larger Stars
As Hydrogen runs out, expands into a Red Supergiant.
Helium fuses into increasingly larger elements.
After Iron, fusion ceases to create energy (This is why Nuclear Fission of larger elements gives off energy)
Once the core turns to Iron, the star ceases to produce energy and collapses inward

18. Supernova!
When a giant star collapses in on itself, it rebounds back outwards in a tremendous explosion known as a supernova.
These supernovas are incredibly bright, outshining their entire galaxy for a brief time.
All elements heavier than Iron are created during these tremendous explosions

19. 400 Year Old
Supernova Remnant

20. 12-25 Solar Masses
Stars 12-25x the mass of our sun leave behind a super dense core known as a neutron star.
A neutron star is made up entirely of neutrons
Only about the size of one human city
Incredibly dense: one thimble’s worth of neutron star would weigh 100 million tons

21. Neutron Stars Continued
Neutron Stars spin extremely fast, rotating several times per second
This is because stars rotate, and as the star shrinks its speed of rotation increases
Neutron stars give off powerful beams of radiation. Every time they spin, we get a burst, like a lighthouse. We call these bursts Pulsars.

23. Escape Velocity
The takeoff speed required to fully escape the gravitational pull of an object
Mass and Radius of an object determine escape velocity
Escape Velocity of Earth: 25,000 mph
Escape Velocity of the Sun: 1.4 Million mph!

24. Stars >25 Solar Masses
When the largest stars collapse, their cores implode into something even more dense than neutron stars
These objects are so dense that the escape velocity is even higher than the speed of light
This means, light cannot escape the pull of gravity
We call these Black Holes

25. Black Holes
Nothing can travel faster than the speed of light, so if light cannot escape a black hole, nothing can.
We cannot observe black holes directly; they give off no light. We can only see their effects, for instance when they bend the light of other stars, or when large stars revolve around them

26. Event Horizon
The boundary of a black hole, past which nothing will ever escape, is called the Event Horizon.
Physicists are still trying to understand the complex warping of space-time that occurs within a black hole.

29. Black Holes (Continued)
Astrophysicists have found evidence of many black holes throughout our observable universe.
In fact, there is evidence that a super large black hole lives in the center of our own galaxy!