Download The Fate of Massive Stars

The Fate of Massive Stars
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Post Main-Sequence Evolution of
Massive Stars
The Classification of Supernovae
Core-Collapse Supernovae
Gamma Ray Bursts
Cosmic Rays
Post-Main Sequence Evolution of Massive Stars
Eta Carinae
•Declination -59 deg 41’ 4.26”
•“fitfully variable” John Herschel
•1837 brightened to Magnitude -1
•Sirius distance = 2.46 pc
•Eta Carinae distance = 2300 pc
• L ~ 2 x 107 LSun
•Bipolar structure visible by HST
•“Homunculus”
•Expanding lobes largely hollow
•Lobe width ~ 0.1 pc
•Contains H2,CH and OH
•Depleted of C and O
•Enriched in He and N
• CNO cycle nuclear processing
•Mass estimated to be ~120 Msun
•Rapid mass loss
What’s going on…?
Luminous Blue Variable Stars (LBV)
•High Effective Temperature 15,000K-30,000K
•Luminosities > 106 L
•Composition of their atmospheres and ejecta
Evolved Post Main-Sequence Star
•Lie in instability region of H-R diagram
•Mass-Loss is important
•L>
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•Large amplitude pulsations?
•High rotation velocity on some LBV
•“weaker” effective gravity
•Still not totally clear…
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http://adsabs.harvard.edu/abs/1994P
ASP..106.1025H
http://berkeley.edu/news/media/relea
ses/2008/09/10_etacar-video.shtml
Wolf-Rayet Stars
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Strong Broad Emission lines
Very hot 25,000K-100,000K !!
High rate of mass loss
– dM/dt > 10-5 M yr -1
– Wind speed 800-3,000 km/s
Rapidly Rotating
– Veq>300 km/s
Very massive: M > 85 M
Less variability than LBVs
•WN: dominated by He and N emission
•WC: dominated by He and C emission
absence of H and N
•WO: prominent O emission lines
•Due to mass loss of star
•Lost hydrogen envelope
•Looking at core of star !!!!
General Evolutionary Scheme for Massive Stars
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For stars with M > 8 M
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Nucleo-synthesis
– Hydrogen burning at core through
CNO cycle
(http://en.wikipedia.org/wiki/CNO_cycle)
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Temperatures sufficient for fusion
of heavier elements in core up to
Iron
– Onion-like layers of Elements
Mass loss- Stellar Winds
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Core collapse
Supernova
General Evolutionary Scheme for Massive Stars
The Humphreys-Davidson Luminosity Limit
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A modification to the Eddington
Luminosity limit that accounts for
increased opacity due to presence of
various Ions (including Fe) in stellar
atmosphere
Diagonal upper-luminosity cutoff that
is temperature dependent
Hotter --> Higher Luminosity cutoff
Greater mass-loss/stellar winds for
cooler stars at lower luminosities
Stellar winds important contribution
to ISM
Massive Stars ability to quench star
formation
Massive stars rare (1 in 1,000,000)
but important role in the evolution of
galaxies
Crab Supernova
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“Guest Stars” have been noted
throughout history…
Bright object appeared in the sky in
1054 …recorded by astrologers in
Europe,China, Japan, Egypt and
Iraq.
A rapidly expanding cloud at the
reported location of the bright object
seen in 1054 is now known as the
Crab Supernova remnant
A pulsar has been identified at this
location as well
Supernovae
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http://supernova.lbl.gov/
Supernovae Spectral Lines
Type I Supernova
Type II-P Supernova
Type II-L Supernova
Supernova Classification Scheme
•Classification by Spectral Lines and Light Curve Shape
•Brightness to rival entire galaxies
•What is happening?
Core Collapse Supernova Mechanism
Core Collapse Supernova Mechanism
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Responsible for Type II,Ib and Ic
Onion-like structure of interior of star
develops
Silicon Burning occurs once temperatures
exceed 3 x 109 K
Any further reactions that produce nuclei
more massive than Iron are endothermic.
As one climbs the curve of binding energy
…less energy per unit mass of fuel
Timescale for each reaction sequence is
progressively shorter
At these high temperatures photons
have enough energy to un-do
nucleosynthesis….highly endothermic
Loss of pressure to support core!!!
Photodisintegration
Core Collapse Supernova Mechanism
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http://en.wikipedia.org/wiki/Type_II_supernova