1. The Fate of High-Mass Stars
Chapter 11
The Fate of High-Mass Stars

2. 11.1 Supernovas
Nova - means “a new star” but are actually stellar explosions
Supernova - a stellar explosion that marks the end of a star’s evolution
Type I Supernovas - occur in binary systems in which one is a white dwarf

4. Type II Supernovas - occur when a massive star’s iron core collapses

5. Energy Budget Fe C He
Energy H
Fusion Stages

6. Type II Supernovae
The star releases more energy in a just a few minutes than it did during its entire lifetime.
Example:
SN 1987A
Brightness
remains high
for hundreds
of days.

7. Supernova 1998S in NGC 3877

8. Type II Supernovae
On July 4, 1054 astronomers in China witnessed a supernova within our own galaxy.

9. Type II Supernovae
After the explosion of a massive star, a huge glowing cloud of stellar debris - a supernova remnant - steadily expands.
Example: Crab Nebula

10. The Crab Nebula

11. Type II Supernovae
After a supernova the exposed core is seen as a neutron star - or if the star is more than 3 solar masses the core becomes a black hole.

12. Energy Output for Type I and Type II
Type II Supernovae
1053 ergs total
Of this 1051 ergs shows up at KE of the ejected shell
and 1050 ergs as light.
Most of the rest is in the escaping neutrinos!
Type I supernovae are more energetic.

14. Relative sizes
Earth
White Dwarf
Neutron Star

15. Neutron Stars ...are stellar remnants for medium-mass stars.
...are found in the centers of some type II supernova remnants.
...have diameters of about 6 miles.
...have masses greater than the Chandrasekhar mass.

16. The Crab Nebula

18. The Crab Pulsar

19. PSR

20. Pulsars Pulsars are rotating, magnitized neutron stars.
The pulsing star inside the Crab Nebula was a pulsar.
Light House Model
Beams of radiation emanate from the magnetic poles.
As the neutron star rotates, the beams sweep around the sky.
If the Earth happens to lie in the path of the beams, we see a pulsar.

22. Rotating Neutron Star

23. Pulsars
The first pulsars observed was originally thought to be a signal from extraterrestrials.
This was later shown to be unlikely after many other pulsars were found all over the sky.
Also, it was found that each pulse had a total power output equal to that of all the resources of Earth.

24. Rotation Rates of Pulsars
The neutron stars that appear to us as pulsars rotate about once every second.
Before a star collapses to a neutron star it probably rotates about once every 25 days.
Why is there such a big difference in rotation rates?
Answer: Conservation of Angular Momentum

26. 11.2.2 Rotation of Neutron Stars
J = Angular Momentum
I = Moment of Interia
w = angular speed
For a sphere...

27. Black Holes ...are stellar remnants for high-mass stars.
i.e. those greater than 3 solar masses
…have a gravitational attraction that is so strong that light cannot escape from it.
…are found in some binary star systems and there may be super-massive black holes in the centers of some galaxies.

30. Cygnus X-1

31. End of Chapter 11

32. Supernova Remnants
Tycho’s SNR

33. Core Remnant
Too massive for electron degeneracy to halt collapse (> 1.4 M)
Electromagnetic force
Neutron Degeneracy can halt collapse
M < 3 M
Strong nuclear force
Neutron Star

34. Pulse Mechanisms Binary Stars - How quickly can two stars orbit?
Two WD about 1m
Two NS about 1s.
Neutron Stars in orbit should emit gravity waves which should be detectable.
Oscillations - Depends only on density
WD about ten seconds
NS about .001s Little variation permitted.
Rotation - Until the object begins to break up.
WD about 1s
NS about .001s with large variation.

35. Glitches

36. Evolutionary Time Scales for a 15 M Star
Nucleosynthesis
Evolutionary Time Scales for a 15 M Star

37. SS 433