white dwarfs and neutron stars - university of...
TRANSCRIPT
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White Dwarfs and Neutron Stars
Stellar Corpses
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Stars: a Comparison
As astronomers collected and compared data from individual stars, a trend became apparent
Spectral type, surface temperature, luminosity and magnitude are closely related
Adding in mass and size, we get a correlation on a chart called a Hertzsprung-Russell diagram
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Stars: a Comparison
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The Life of a Star
Nuclear fusion inside the cores of stars creates energy
What happens when all of the nuclear fuel (hydrogen) is used up?
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The Life of a Star
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The Life of a Star
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The Death of a Star
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White Dwarfs
Small Carbon and Oxygen inert core of once active main sequence stars
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White Dwarfs
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White Dwarfs
By accumulating mass (hydrogen), periodic bursts of fusion can occur on the surface called a nova
If too much mass is accumulated, the explosion may take place within the star blowing it apart in a supernova
Supernovae can also happen if two white dwarfs collide
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CfA press release
Evidence of merging white dwarfs exploding: supernova 2006gz
SN 2006gz shows strong spectral signature of unburned carbon pushed away by the merger
Spectrum also shows silicon created during the explosion
Brighter than most white dwarf supernovae, suggesting more mass than the Chandrasekhar limit (1.4 solar masses) would allow
Dwarf Sibling Rivalry Explodes into Supernova. Release Number 2007-29. http://www.cfa.harvard.edu/news/2007/pr200729.html
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White Dwarf Fact Sheet
Composed of Carbon and Oxygen Is no longer actively creating energy
through thermonuclear fusion Peak emission in Ultraviolet Radius comparable to Earths Mass limit of about 1.4 solar masses Can explode into novae and supernovae
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High Mass Stars
Above 8 solar masses (less massive stars will blow off their outer layers into planetary nebulae and the core remains as a white dwarf)
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High Mass Stars
Additional stages of fusion in the core
Stops at iron (more energy input required)
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High Mass Stars
Core rapidly contracts and heats to around 5 billion degrees
Previously large core shrinks to less than 20 kilometers in diameter
Core becomes so dense that the protons and electrons fuse into neutrons
Inner part of the core bounces and produces a shockwave that triggers a supernova explosion
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Neutron Stars The remnants of the core after a
supernova has blasted the rest of the star into space
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Neutron Stars Have an upper mass limit of around 3 solar
masses (heavier cores of very massive stars collapse forming a black hole)
Hypothesized to exist long before the discovery of pulsars (rapidly spinning neutron stars that emit beams of radiation)
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Pulsars
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Neutron Stars
By accumulating mass (helium), periodic bursts of fusion can occur on the surface and create an X-ray burster
Can collide or merge with each other (or black holes), creating a gamma ray burst (the most powerful explosions in the universe)
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Spitzer press release Neutron stars can form powerful jets of
matter and energy Previously only thought possible with black
holes Binary system with neutron star gaining
matter from white dwarf companions atmosphere in an accretion disk
Neutron star is tiny compared to white dwarf but is very dense and about 14 times as massive
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Spitzer press release
Staff Writers. May 22, 2006. Stellar Jets. Spitzer. http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=sig06-014
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Neutron Star Fact Sheet
Composed largely of neutrons, with some protons and possibly exotic states of matter
Is no longer actively creating energy through thermonuclear fusion
Peak emission in X-ray (not always from the star itself)
Radius comparable to Winnipegs Mass limit of about 3 solar masses
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Sources and Links Freedman RA, Kaufmann III WJ, 2005. Universe: New York: W. H. Freeman and Company. 693pp. 7th ed. Staff Writers. September 24, 1997. Hubble Sees a Neutron Star Alone in Space.
Release Number STScI-1997-32. http://hubblesite.org/newscenter/archive/releases/1997/32/ Staff Writers. May 22, 2006. Stellar Jets. Spitzer. http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=sig06-014 Staff Writers, Harvard-Smithsonian Center for Astrophysics. November 1, 2007.
White Dwarf Sibling Rivalry Explodes into Supernova. Release Number 2007-29. http://www.cfa.harvard.edu/news/2007/pr200729.html link to the paper: http://arxiv.org/PS_cache/arxiv/pdf/0709/0709.1501v1.pdf Staff Writers, Harvard-Smithsonian Center for Astrophysics. January 31, 2006.
Neutron Star Swaps Lead to Short Gamma Ray Bursts. Release Number 2006-12.
http://www.cfa.harvard.edu/news/2006/pr200612.html link to the paper: http://www.nature.com/nphys/journal/v2/n2/full/nphys214.html
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List of Images Used 1) Hertzsprung-Russell Diagram 1 Universe 7th ed. page 428 2) Hertzsprung-Russell Diagram 2 Universe 7th ed. page 428 3) Fusion of Hydrogen into Helium Universe 7th ed. page 381 4) Main Sequence to Red Giant Universe 7th ed. page 471 5) Red Giant Sun Universe 7th ed. page 470 6) Mass Ejection Universe 7th ed. page 494 7) Sirius B White Dwarf Star Universe 7th ed. page 495 8) White Dwarf Mass Radius Relation Universe 7th ed. page 495 9) Fusion Layers in a Supergiant Star Universe 7th ed. page 498 10) Neutron Star Section Universe 7th ed. page 520 11) Neutron Pulsar Universe 7th ed. page 516 12) White Dwarf and Neutron Star Jets Spitzer press release,
NASA/JPL-Caltech/R. Hurt (SSC)