The Fate of Massive Stars
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Transcript of The Fate of Massive Stars
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The Fate of Massive Stars
• Post Main-Sequence Evolution of Massive Stars
• The Classification of Supernovae• Core-Collapse Supernovae• Gamma Ray Bursts• Cosmic Rays
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Post-Main Sequence Evolution of Massive Stars
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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 lossWhat’s going on…?
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Luminous Blue Variable Stars (LBV)
• http://adsabs.harvard.edu/abs/1994PASP..106.1025H
• http://berkeley.edu/news/media/releases/2008/09/10_etacar-video.shtml
•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> ?
•Large amplitude pulsations?
•High rotation velocity on some LBV•“weaker” effective gravity
•Still not totally clear…
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Wolf-Rayet Stars
• 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 !!!!
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General Evolutionary Scheme for Massive Stars
• For stars with M > 8 M
• Nucleo-synthesis – Hydrogen burning at core through
CNO cycle (http://en.wikipedia.org/wiki/CNO_cycle)
– Temperatures sufficient for fusion of heavier elements in core up to Iron
– Onion-like layers of Elements• Mass loss- Stellar Winds
• Core collapse
Supernova
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General Evolutionary Scheme for Massive Stars
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The Humphreys-Davidson Luminosity Limit
• 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
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Crab Supernova
• “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
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Supernovae
• http://supernova.lbl.gov/
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Supernovae Spectral Lines
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Type I Supernova
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Type II-P Supernova
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Type II-L Supernova
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Supernova Classification Scheme
•Classification by Spectral Lines and Light Curve Shape•Brightness to rival entire galaxies•What is happening?
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Core Collapse Supernova Mechanism
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Core Collapse Supernova Mechanism
• 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 endothermicLoss of pressure to support core!!!
Photodisintegration
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Core Collapse Supernova Mechanism
• http://en.wikipedia.org/wiki/Type_II_supernova