Download White Dwarfs and Neutron Stars

White Dwarfs and
Neutron Stars
Stellar Corpses
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
Stars: a Comparison
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?
The Life of a Star
The Life of a Star
The Death of a Star
White Dwarfs
• Small Carbon and Oxygen inert core of
once active main sequence stars
White Dwarfs
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
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
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Dwarf “Sibling Rivalry” Explodes into Supernova. Release Number 2007-29.
http://www.cfa.harvard.edu/news/2007/pr200729.html
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 Earth’s
• Mass limit of about 1.4 solar masses
• Can explode into novae and supernovae
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)
High Mass Stars
• Additional stages of fusion in the core
• Stops at iron (more energy input required)
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
Neutron Stars
• The remnants of the core after a
supernova has blasted the rest of the star
into space
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)
Pulsars
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)
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 companion’s
atmosphere in an accretion disk
• Neutron star is tiny compared to white
dwarf but is very dense and about 14
times as massive
Spitzer press release
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Staff Writers. May 22, 2006. Stellar Jets. Spitzer.
http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=sig06-014
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 Winnipeg’s
• Mass limit of about 3 solar masses
Sources and Links
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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
List of Images Used
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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)