Stellar Death The Evolution of Massive Stars

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Stellar Death The Evolution of Massive Stars

• Neutron Stars BlackHoles

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Stars with a masses less than about 25 solar
masses but more than 8 solar masses
Main Sequence Star ? Red Giant ? SuperGiant ?
Supernova Explosion ? Neutron Star
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This is the end..
The end of stellar evolution is an inert core of
spent fuel that cannot maintain gas pressure to
balance gravity
Such a core can be balanced against gravitational
collapse by electron degeneracy pressure IF the
total mass is less than the Chandrasekhar mass
limit
Chandrasekhar Mass
Only if the mass of a inert core is less than
Chandrasekhar Mass Mch
MCh1.46 M?
Electron degeneracy pressure can prevent
gravitational collapse
In more massive cores electrons become
relativistic and gravitational collapse occurs.
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Large Scale Mass Loss Large Mass, HUGE
Luminosity, Strong Winds
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Fusing Main Fusion Products H He He C, O
C Ne, O Ne O O S, Si, Ar Si Fe, Cr
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Whats next? Iron (Fe) Fusion. Good? BAD! Why?
Iron fusion doesnt produce energy - it consumes
energy, energy that should help maintain the
cores structure. Iron fuses, core collapses,
core gets hotter, fuses iron faster.
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The end is near
A vast quantity of Neutrinos are produced. What
about the rest of the star? Rest of star
collapses on tiny core very dense core of pure
neutrons Iron Core Bounce! Huge energy generation
Iron fusion causes the core to collapse in 1/4 of
a second. Neutronization occurs p e ? n ?
Core becomes a small ball of neutrons. How
small? About 20 km wide.
Expels layers out - big star go BOOM!
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Supernova Explosion
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Supernovae Factoids
Luminosity
Supernovae might be the brightest objects in the
universe, and can outshine a whole galaxy (for a
few weeks)
Energy of the visible explosion
Huge!!!Luminosity
109-10 L?
Frequency
1-10 per century per galaxy
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Supernova!
Very important event because very bright -
visible over a great distance, for a long
time explosion spreads material out - material
that goes into new stars can trigger new star
formation energy goes into producing heavy
elements release of neutrinos!! Hot topic of
astrophysics research Stellar Corpses neutron
star or blackhole
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Since Supernova are rare, look at what is left
behind Supernova Remnants - hot gas cloud left
behind by supernova Remain hot for a long
time Sometimes visible in x-rays, many visible in
radio Size of remnant and expansion velocity
clue to age
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Tycho Brahes Supernova
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HST picture Crab nebula SN July 1054 AD Dist
6500 ly Diam 10 ly, pic size 3
ly Expansion 3 mill. Mph (1700 km/s)
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Visible
X-ray
IR
Radio
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Then one day in 1987 (February 23, 1987 to be
exact)
Tarantula Nebula in LMC (constellation Dorado,
southern hemisphere) size 2000ly (1ly 6
trillion miles), distance 180000 ly
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Then one day in 1987 (February 23, 1987 to be
exact)
Tarantula Nebula in LMC (constellation Dorado,
southern hemisphere) size 2000ly (1ly 6
trillion miles), distance 180000 ly
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Supernova 1987A (SN87A)
The best observed supernova of all time! Visible
to the naked eye - first since 1604! Star that
went supernova (Sanduleak -69 202) was previously
studied. Observation of neutrinos! Observation of
nucleosynthesis (production of heavy
elements) And today we see..
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SuperNova Light Curve
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Supernova remnants neutron stars
SN remnant Puppis A (Rosat)
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Isolated neutron star seen with Hubble Space
Telescope
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Where did heavy elements come from?
Heavy element abundances are (roughly) what
results from supernova explosions. Lighter
elements (C, N, O, . . . up to Fe) are produced
in fusion reactions before the explosion Heavier
elements are produced in the explosion itself
We are stardust, We are billion year old
carbon. -- Joni Mitchell, 1969
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Pulsars?
In 1967 Jocelyn Bell (1943 - ) a graduate student
working with a group of English astronomers,
headed by her advisor Anthony Hewish (1924- ),
noticed an odd radio signal with a rapid and
astonishingly precise pulse rate of one energetic
burst every 1.33 seconds.
Over the next few months the group found several
more pulsating radio sources, some of which were
definitely associated with the inner most regions
of some supernova remnants.
These repeating sources were named, Pulsars.
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LightHouse Model
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