Presentation on theme: "The Fate of Massive Stars Post Main-Sequence Evolution of Massive Stars The Classification of Supernovae Core-Collapse Supernovae Gamma Ray Bursts Cosmic."— Presentation transcript:
The Fate of Massive Stars Post Main-Sequence Evolution of Massive Stars The Classification of Supernovae Core-Collapse Supernovae Gamma Ray Bursts Cosmic Rays
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 10 7 L Sun Bipolar structure visible by HST “Homunculus” Expanding lobes largely hollow Lobe width ~ 0.1 pc Contains H 2,CH and OH Depleted of C and O Enriched in He and N CNO cycle nuclear processing Mass estimated to be ~120 M sun Rapid mass loss What’s going on…?
Luminous Blue Variable Stars (LBV) http://adsabs.harvard.edu/abs/1994P ASP..106.1025Hhttp://adsabs.harvard.edu/abs/1994P ASP..106.1025H http://berkeley.edu/news/media/relea ses/2008/09/10_etacar-video.shtmlhttp://berkeley.edu/news/media/relea ses/2008/09/10_etacar-video.shtml High Effective Temperature 15,000K-30,000K Luminosities > 10 6 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…
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 –V eq >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 For stars with M > 8 M Nucleo-synthesis –Hydrogen burning at core through CNO cycle (http://en.wikipedia.org/wiki/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
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
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
Responsible for Type II,Ib and Ic Onion-like structure of interior of star develops Silicon Burning occurs once temperatures exceed 3 x 10 9 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