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

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 Earths 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 companions 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

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 Winnipegs Mass limit of about 3 solar masses

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

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)