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Transcript
Stellar Death
High Mass Stars
Nucleosynthesis
Evolutionary Time Scales for a 15 M Star
Fused
Products
H
4He
107 yrs.
40 X 106 K
4He
12C
Few X 106 yrs
1 X 108 K
1000 yrs.
6 X 108 K
16O, 24Mg
Few yrs.
1 X 109 K
28Si, 32S
One year
2 X 109 K
Days
3 X 109 K
< 1 second
> 3 X 109 K
16O, 20Ne,
12C
20Ne
24Mg, 4He
+
16O
28Si
+
56Fe
56Fe
Neutrons
Time
Temperature
Energy Budget
H
Used energy
Released energy
He
C
Fusion Stages
Fe
Animation
The Final Second
 Fe fusion begins
 Energy debt results
 Core contracts - temperature increases
Uncontrollable gravitational collapse
vNuclei converted back into He
He  protons and neutrons
proton + electron  neutron + neutrino
vCore Implodes  Envelope Explodes
Supernova
Anazasi Pictographs
The Crab Nebula
Supernova 1987a
Supernova 1998S in
NGC 3877
Supernova Remnants
Tycho’s SNR - 1572
Core Remnant
 Too massive for electron degeneracy
to halt collapse (> 1.4 M)
 Neutron Degeneracy can halt collapse
 M < 3 M
 Strong nuclear force
 Neutron Star
Properties of a Neutron Star
 Very small
 Gravity balanced by strong nuclear force
 R = 10 km
 Very Faint
 Rapid rotation
 Conserve angular momentum
 1000 rotations/s
 Intense Magnetic Field
 One trillion gauss
PSR 0628-28
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
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.
To Darken the Sun
Time Delay = Radius/c
500,000 km/300,000 km/s = 1.67 sec
Only candidates: White Dwarfs, Neutron Stars
Pulse Mechanisms
 Binary Stars - How quickly can two stars orbit?
o Two WD about 1m
o Two NS about 1s.
o Neutron Stars in orbit should emit gravity waves which should
be detectable.
 Oscillations - Depends only on density
o WD about ten seconds
o NS about .001s Little variation permitted.
 Rotation - Until the object begins to break up.
o WD about 1s
o NS about .001s with large variation.
The Crab Pulsar
Rotating Neutron Star
Lighthouse Model
Synchrotron Radiation
Radiation
Magnetic lines of force
Electron
Glitches
SS 433
Relative sizes
Earth
White Dwarf
Neutron Star
Mass Limits
 Low mass stars
 Less than 8 M on Main Sequence
 Become White Dwarf (< 1.4 M)
 Electron Degeneracy Pressure
 High Mass Stars
 Less than 40 M on Main Sequence
 Become Neutron Stars (3 M < M <1.4 M)
 Neutron Degeneracy Pressure
Supermassive Stars
 If stellar core has more than three
solar masses after supernova, then no
known force can halt the collapse
Black Hole
Space-Time
No mass
Distortion
caused by
mass
Predictions of General
Relativity
 Advance of Mercury’s perihelion
 Bending of starlight
Advance of Mercury’s Perihelion
Advance in arcsec/cen
5599
total advance with respect to the
geocenter.
5025
contribution of precession of
Earth's equinoxes.
531
Classical or Newtonian
contribution of the other planets.
43
General relativity correction
(modern theory: 42.98)
Bending of Starlight
Apparent position
of the star
Sun
Light from star bent by
the gravity of the Sun
Low Gravity
Very small
amount of
bending
Stronger Gravity
Light at an angle is
bent noticeably
Exit Cone and
Photon Sphere
Photon Sphere
Near a Black Hole
Schwarzschild Black Hole
Event Horizon
Rs = 3(Mass)
+
Rs
Singularity
Mass
Rs
3 M
9 km
5
15
10
30
What Can We Know?
 Mass
 gravity
 Charge
 Electric Fields
 Rotation Rate
 Co-rotation
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
Cygnus X-1