1. The Bizarre Stellar Graveyard
Chapter 14
The Bizarre Stellar Graveyard

2. White Dwarfs... ...are stellar remnants for low-mass stars.
...are found in the centers of planetary nebula.
...have diameters about the same as the Earth’s.
...have masses less than the Chandrasekhar mass.

3. Sirius B is a white dwarf star

4. Sirius A And Sirius B In X-ray

5. Novas and Supernovas Nova - a stellar explosion
Supernova - a stellar explosion that marks the end of a star’s evolution
White Dwarf Supernova (Type I supernova)- occur in binary systems in which one is a white dwarf
Massive Star Supernova (Type II Supernova) - occur when a massive star’s iron core collapses

6. Close Binary Systems and Mass Transfer

7. Nova Herculis
March 1935
May 1935

8. Diagram of nova process

9. Nova T Pyxidis
(HST)
A nova occurs when hydrogen fusion ignites on the surface of a white dwarf star system

10. Light Curve of typical Nova

11. Semidetached Binary System With White Dwarf Star (may result in a white dwarf (type I ) supernova)

12. Type II Supernova
The star releases more energy in a just a few minutes than it did during its entire lifetime.
Example: SN 1987A
After the explosion of a massive star, a huge glowing cloud of stellar debris - a supernova remnant - steadily expands.
Example: Crab Nebula
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.

13. The remnant of this explosion is The Crab Nebula
On July 4, 1054 astronomers in China witnessed a supernova within our own galaxy.
The remnant of this explosion is The Crab Nebula

14. Supernova 1987a

15. Type I and Type II Supernova

16. Supernova Light Curves

17. Hydrogen and Helium Burning

19. Carbon Burning and Helium Capture

20. Still heavier elements are created in the final stages of life of massive stars

21. Alpha Process – Helium Capture produces heavier elements up to Fe and Ni.

22. Elements beyond Fe and Ni involve neutron capture.
This forms unstable nuclei which then decay into stable nuclei of other elements
Formation of Elements beyond Iron occurs very rapidly as the star approaches supernova.

23. The supernova explosion then distributes the newly formed matter throughout the interstellar space (space between the stars).
This new matter goes into the formation of interstellar debris.
The remnant core is a dense solid core of neutrons – a neutron star!

24. Neutron Stars ...are stellar remnants for high-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. (1.4M)

25. Relative Sizes
Earth
White Dwarf
Neutron Star

26. Pulsars
The first pulsar observed was originally thought to be signals from extraterrestrials.
(LGM-Little Green Men was their first designation)
Period = seconds exact!
~ 20 seconds of Jocelyn Bell’s data- the first pulsar discovered

27. It was later shown to be unlikely that the pulsar signal originated from extraterrestrial intelligence after many other pulsars were found all over the sky.

28. Pulsars The pulsing star inside the Crab Nebula was a pulsar.
Pulsars are rotating, magnetized neutron stars.

29. The Crab Nebula

30. Period = 0.033 seconds = 33 milliseconds
The Crab Pulsar
Period = seconds = 33 milliseconds

31. 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.

32. Rotating Neutron Star

33. Light House model of neutron star emission accounts for many properties of observed Pulsars

34. Artistic rendering of the light house model

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

37. Neutron –Star Binaries

38. Mass Limits Low mass stars High Mass Stars
Less than 8 M on Main Sequence
Become White Dwarf (< 1.4 M)
Electron Degeneracy Pressure
High Mass Stars
Less than 100 M on Main Sequence
Become Neutron Stars (1.4M < M < 3M)
Neutron Degeneracy Pressure

39. Black Holes ...are stellar remnants for high-mass stars.
i.e. remnant cores with masses 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.

40. Supermassive Stars Black Hole
If the stellar core has more than three solar masses after supernova, then no known force can halt the collapse
Black Hole
Black holes were first predicted by the General Theory of Relativity, which is theory of gravity that corrects for some of the short-falls of Newton’s Theory of Gravity.

41. In general Relativity, space, time and mass are all interconnected

42. Distortion caused by mass
Space-Time
No mass
Distortion caused by mass

43. Predictions of General Relativity
Advance of Mercury’s perihelion
Bending of starlight

44. Advance of Mercury’s Perihelion
43” per century not due to perturbations from other planets

45. Bending of Starlight 1.75” Sun Apparent position of the star
Light from star bent by the gravity of the Sun
Sun

46. Schwarzschild Black Hole Schwarzchild metric- non-rotating black holes
ds2 = [1-(2m/r)]dt2 – [1-(2m/r)]-1dr2 - r2dq2 - r2sin2qdf2
Event Horizon Rs
Rs = 3(Mass)
Mass Rs
3 M km
Singularity +

47. Near a Rotating Black Hole (Kerr Metric – “frame dragging”)

48. What Can We Know? Mass Charge Rotation Rate gravity Electric Fields
Co-rotation

49. How Can We Find Them? Look for X-ray sources
Must come from compact source
White Dwarf
Neutron Star
Black Hole
Differentiate by Mass
WD - < 1.4 M
NS - between 1.4 and 3 M
BH - > 3 M

50. Cygnus X-1

51. The mass of a neutron star must be less than
1 solar mass
1.4 solar mass
2 solar mass
3 solar mass

52. Which is closest to the size of a white dwarf star
The Sun
Texas
The Earth
A Red Giant

53. End of Chapters

54. End of Section.

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

56. Energy Budget Fe C He
Energy H
Fusion Stages

57. Anazasi Pictographs

58. Supernova 1998S in NGC 3877

59. Supernova Remnants
Tycho’s SNR

60. PSR

61. LGM?
Several more found at widely different places in the galaxy
Power of a power equals total power potential output of the Earth
No Doppler shifts
PULSARS

62. Light Time Argument
An object which varies its light can be no larger than the distance light can travel in the shortest period of variation.

63. To Darken the Sun Time Delay = Radius/c
500,000 km/300,000 km/s = 1.67 sec

64. Only candidates: White Dwarfs, Neutron Stars

65. 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.

66. SS 433

67. Synchrotron Radiation
Magnetic lines of force
Electron

68. Glitches