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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 – PowerPoint PPT presentation

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Title: The Fate of Massive Stars


1
The Fate of Massive Stars
  • Post Main-Sequence Evolution of Massive Stars
  • The Classification of Supernovae
  • Core-Collapse Supernovae
  • Gamma Ray Bursts
  • Cosmic Rays

2
Post-Main Sequence Evolution of Massive Stars
3
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

Whats going on?
4
Luminous Blue Variable Stars (LBV)
  • High Effective Temperature 15,000K-30,000K
  • Luminosities gt 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
  • Lgt ?
  • Large amplitude pulsations?
  • High rotation velocity on some LBV
  • weaker effective gravity
  • Still not totally clear
  • http//adsabs.harvard.edu/abs/1994PASP..106.1025H
  • http//berkeley.edu/news/media/releases/2008/09/10
    _etacar-video.shtml

5
Wolf-Rayet Stars
  • Strong Broad Emission lines
  • Very hot 25,000K-100,000K !!
  • High rate of mass loss
  • dM/dt gt 10-5 M? yr -1
  • Wind speed 800-3,000 km/s
  • Rapidly Rotating
  • Veqgt300 km/s
  • Very massive M gt 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 !!!!

6
General Evolutionary Scheme for Massive Stars
  • For stars with M gt 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

7
General Evolutionary Scheme for Massive Stars
8
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 --gt 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

9
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

10
Supernovae
  • http//supernova.lbl.gov/

11
Supernovae Spectral Lines
12
Type I Supernova
13
Type II-P Supernova
14
Type II-L Supernova
15
Supernova Classification Scheme
  • Classification by Spectral Lines and Light Curve
    Shape
  • Brightness to rival entire galaxies
  • What is happening?

16
Core Collapse Supernova Mechanism
17
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
endothermic Loss of pressure to support
core!!! Photodisintegration
18
Core Collapse Supernova Mechanism
  • http//en.wikipedia.org/wiki/Type_II_supernova
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