1. Death of Stars (for high mass stars)

2. Death of Stars Remember: What a star evolves into depends on its MASS.
After the main sequence, a star could become…….
White dwarfs (low mass…size of sun or smaller)
pulsars (heavier stars…like blue giants)
black holes (heaviest stars…like blue giants)

3. Review Same as before, but faster…
1. intersteller cloud of dust
2. protostar
3. main-sequence star but as a BLUE GIANT
4. Red Supergiant-- When a high-mass star exhausts the hydrogen fuel in its core the star leaves the main sequence and begins to burn helium.

5. The Structure of the Core of a Star Just Before It Erupts as a Supernova
When helium is depleted, fusion of heavier elements begins. This process is called nucleosynthesis.
H -> He -> C -> O -> Si -> Fe
(eventually goes to IRON)
When the final product is iron in the core, no more energy…so it collapses.

6. Why is iron (mass number = 56) the last stage?
Atoms will naturally fuse into more stable nuclei
You can’t get more energy out of fusing iron

7. B. Carbon core contracts causing
1. Pressure to rise
2. Temp. to rise to 600 million K
C. Higher temps. Cause carbon fusion cycle that will eventually end in iron.

8. Steps in the Explosion of a Supernova
D. formation of iron ends the fusion cycle and star contracts one last time and rebounds off the dense core

9. Kaboom! 1. Luminosity--100 billion times brighter than the sun
2. produces wave of neutrinos, elements heavier than Fe, shock waves in nebulae

10. SN 1987A

11. Supernova G. Example: SN 1987A
1. Where? --in Large Magellanic Cloud (S. hemisphere)
2. When? (duh)
3. What was found?--neutrinos…as the theory predicted

12. Neutrino detector

13. The Brightness of a Typical Type II Supernova for 100 Days After the Supernova Reached Maximum Brightness

14. Neutron Stars A. Description
1. Extremely dense star after shedding outside layers
2. Mass is about 1.4 to 3 solar masses
3. Size is about 10 km across (small!)
4. Density is about 3 x 1014 g/cm3 ( 1cm3 of neutron star equals 340 m3 of steel!!!)
(artist’s rendition)

15. Pulsars 1. Pulsars are neutron stars that rotate
a. NOT normal stars…the rotation period is to 10 seconds (fast!)
2. Have extremely intense magnetic fields
a. result--rips apart particles at surface
b. accelerated electrons emit synchotron radiation
c. like a lighthouse

16. A Model of a Pulsar
We can maybe see them if we are lined up with the beams of radiation

17. Crab Pulsar Animation

18. One Hundred
Consecutive Pulses
from
PSR

19. Crab Pulsar Ex. Crab Pulsar inside the crab nebula
The pulsar is within the left over supernova remnant from 1054 A.D.

20. So What Effect does Gravity have on spacetime?
Spacetime has 4 coordinates:
x-axis, y-axis, z-axis (3-D) and time
Mass bends spacetime in general. (Einstein)
Black holes (supermassive) bend spacetime a lot !

21. Flat and Curved Two-Dimensional Spaces

22. Paths of a Marble and the Television
Image of the Paths for the Cases of
Flat and Curved Space

23. Black Holes A. Not really a hole
B. A dense star that continues to collapse
1. So dense and gravity is so strong that light can’t escape
C. Event horizon--ring around black hole where light couldn’t escape
D. Scharzshild radius--the radius a star has to have to become a black hole

24. Black holes
1. For sun to become a black hole--it would have to collapse to at least 3 km
2. For the earth to become a black hole--it would have to collapse to 1 cm

25. The Paths of Light Rays Aimed Outward in Different Directions from the
Collapsing Core of a Star

26. A visual diagram of how a black hole may bend spacetime.
However, you don’t “see” this (it’s not like a waterslide).

27. Artist’s drawing of a black hole
If we can’t “see” them, how do we know they are there?
1. Accretion disk
2. Galactic jets
3. X-rays from the disk
4. A companion star orbiting “nothing”
Note: The bright center is not the black hole, just energetic material around it.
Galactic jets
Accretion disk
X-rays

28. Cygnus X-1 Distance--2500 pc (8000 ly away)
where?--in constellation Cygnus
discovered in 1966
a. blue supergiant companion that orbits it
b. intense x-rays (as seen in picture)