Download Time From the Perspective of a Particle Physicist

Supernova and Neutron Stars
For heavy white dwarves with a companion star
• acquire mass, if becomes > 1.4 M(Sun)
SUPERNOVA (Ia). p + e  n + neutrino
• Usually leaves neutron star
For high mass stars
• fusion continues beyond C,O to Iron
• if Mass(core) > 1.4 M(Sun) core collapses in
SUPERNOVA (II)
• leaves either Neutron Star or Black Hole
• Most SN are this type
PHYS 162
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Supernovas and Core Collapse
• massive stars have fusion to heavier nuclei
(Neon, Silicon, Sulpher, etc)
• end up with core of Iron nuclei plus 26 unbound
“free” electrons for every Fe
• electrons are “degenerate” as so close together 
provide most of the pressure resisting gravity
• enormous stress. electrons “give way” leaves
“hole” size of Earth in center of star
PHYS 162
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Supergiant  Iron Core
PHYS 162
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During Supernova
core collapse gives 200 billion degrees  very high
energy photons
• breaks up many nuclei
Fe  26p + 31n O  8p + 8n
• new nuclei form  photons, n, and p strike shell around
core  see in SN debris
• p + e  n + neutrino (and nuclei decaying)
1. Burst of neutrinos. 1000 times more energy than from
light (photons)
2. Leftover neutron star
•
PHYS 162
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Core Collapse
core collapses into
mostly neutrons –
very hot
outer layers rush into
“hole” smashing into
shock wave from core
Many nuclear
reactions  form
heavy elements
Core=30 km wide
Hole=13000 km wide
Type II expends
energy increasing size
PHYS 162
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Supernova Explosions
1 billion times brighter
then the Sun for a few
months
PHYS 162
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Supernova 1987a (in movie)
Large Magellanic
Cloud Type II
180,000 LY away
PHYS 162
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Detection of neutrinos from SN1987A in Japan
and Ohio
SN produced 1058 neutrinos
1015 n/cm2 at Earth
1018 neutrinos from SN passed
through any person’s body
Traveled 175,000 light years to Earth
Passed through Earth
24 were detected in detectors made from 100
tons of water located in underground mines
in Ohio, Russia and Japan
PHYS 162
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Nuclear Synthesis
•
All elements heavier than Helium are made inside
stars
up to Iron - fusion in Red Giants
heavier than Iron (and some lighter) - Supernova
explosions
• Stars lose matter at end of life-cycle
becoming Red Giants (can detect)
Supernova debris (can detect)
and this matter forms new stars (and planets and us
– “we are stardust” Joni Mitchell, Woodstock)
PHYS 162
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Cosmic Abundance of Elements
H = 92% of elements = mass-fraction 74%
He = 8%
= mass-fraction 25%
All others < 1% mass-fraction about 1%
Discovered by Cecilia Payne about 1921, but she didn’t
become Harvard faculty until 1956 as “no female faculty”
PHYS 162
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Supernova Debris SN1987a
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Supernova Debris
Crab Nebula M1
Cassiopeia A maybe
Supernova 1054 (observed by
observed in 1680
Chinese and Arabs). Has neutron
PHYS 162
star
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NEUTRON STARS
In supernova explosion core collapses
• e- + p  n + n
• neutrons remain giving neutron “star” about
1% protons/electrons
• very hot (200 billion degrees) and very small
(10-30 km - DeKalb County)
• so very, very dense. 1 cm3  100 million tons
PHS 162
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White Dwarf
Neutron Star
Mass (relative to
Sun)
Radius
1.0 (always <
1.4)
5000 km
1.5 (always <
3)
10 km
Density
106 g/cm3
1014 g/cm3
Properties determined by “degenerate” electrons and neutrons.
neutron/electron mass ratio = 2000, neutron star much smaller and
denser
Senior level physics classes do the quantum mechanics which
predict radius versus mass
PHS 162
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HR Digram Worksheet
• For Sirius B use spectral class B1
• Vertical axis is Luminosity and a log scale so do .00001,
.0001, .001, .01, .1, 1, 10, 100, 1000, 10,000, 100,000,
1,000,000 with 2,3 or 4 lines separating each
• After labeling horizontal axes with spectral class B0M10, add on below them the surface temperature with:
B0= 24,000 A0=11,000 F0=7000 G0=6000
K0=5000 M0=4000
PHYS 162
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HertzprungRussell Diagram
Plot Luminosity
versus surface
temperature
PHYS 162
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