Download Supernovas 10/19

Supernova Explosions
1 billion times brighter
then the Sun for a few
months
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Supernovas
• 10-20 supernovas occur every1000 years in
a galaxy the size of the Milky Way (~200
billion stars) with ~15% being type Ia
• 8 observed in last 2000 years (185, 386,
393, 1006, 1054, 1181, 1572, 1604)
• Hard to observe if on “opposite” side of
Milky Way  all recent observed SN are in
other galaxies
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1572 (Tycho Brahe) and 1604 (Kepler)
In Milky Way both probably Type Ia
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Supernova 2014j – Jan 2014
In M82 (Ursa Major). Type Ia. Closest of this type
observed in modern times. 11.5 million LY away.
Discovered at undergrad session Univ Coll London
(SN1972 e was 11 MLY but pre “modern”)
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Supernova PTF 11kly – Sept 2011
In Pinwheel Galaxy. Type Ia. 2nd closest Ia
observed in modern times. 21 million LY away
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Supernova 1987a (in movie)
Large Magellanic
Cloud Type II
180,000 LY away
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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. This causes them to provide most
of the pressure resisting gravity
• enormous stress. If electrons “give way”
leaves “hole” in center of star
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Supergiant  Iron Core
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During Supernova
core collapse gives 200 billion degrees  energetic
photons
• breaks up many nuclei
Fe  26p + 31n O  8p + 8n
• new nuclei form  photons, n, and p strike shell around
core
• p + e  n + neutrino
1. Burst of neutrinos. 1000 times more energy than from
light (photons)
2. Leftover neutron star
•
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Core Collapse
core collapses into
mostly neutrons –
very hot
outer layers rush
into “hole”
smashing into
shock wave from
core
happens when
mass of core > 1.4
Mass Sun.
Chandrashekar
limit
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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
17 were detected in detectors made from 100
tons of water located in underground mines
in Ohio and Japan
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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)
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Nuclear Synthesis during Supernova
•
mostly neutrons attaching themselves to nuclei say
Fe(26p + 31n)  U(92p + 146n)
• new nuclei form that have 10-20-50 “too many” neutrons
• they Beta decay n  p very rapidly now having nuclei
with more protons than Iron
• Cycle repeats itself – happens very fast “rapid”
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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 1856 as “no female faculty”
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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
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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
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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
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HR Diagram 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 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
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HertzprungRussell Diagram
Plot Luminosity
versus surface
temperature
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