The Fate of Massive Stars

• 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 lossWhat’s going on…?

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…

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 !!!!

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

General Evolutionary Scheme for Massive Stars

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

Supernovae

• 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

• 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

Core Collapse Supernova Mechanism

• http://en.wikipedia.org/wiki/Type_II_supernova