Transcript Still More Pulsars

After the Supernova:
Pulsars
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Melissa Anholm
University of Wisconsin-Milwaukee
29 September, 2008
Outline
• Properties of Neutron Stars
• Large Magnetic Field
• Rapid Rotation
• Origin of the Pulsing Effect
• Motion in a Magnetic Field
• Light Emission
• The Lighthouse Effect
Properties of Neutron Stars
A Typical
Neutron Star
• Strong Magnetic Field
• Fast Rotation
Properties of Neutron Stars
Why does it spin so fast?
A typical star
completes about
one rotation every
week - month.
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A typical young
pulsar completes
about one rotation
per second.
Properties of Neutron Stars
Magnetic Fields - Now with Lines!
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http://www.freewebs.com/ayxl/magnet.jpeg
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http://www.utm.edu/staff/cerkal/magnetic_files/image004.jpg
Properties of Neutron Stars
After the Collapse:
Rotation and the Magnetic Field
• Dense magnetic field lines
 Strong magnetic field
• Angular momentum conserved
 Fast rotation
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• Magnetic and rotational
axes may not be aligned.
Origin of the Pulsing Effect
Misalignment of Magnetic and
Rotational Axes - Why We Care
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http://www.atnf.csiro.au/news/press/images/binary_pulsar/
All newly formed
neutron stars (and
some older ones,
too!) produce beams
of light along their
magnetic poles if the
axes aren’t aligned.
Origin of the Pulsing Effect
Properties of Light
• “photon” = a particle of light
• accelerating charged particles produce photons (!)
Origin of the Pulsing Effect
A Strange Connection
between Electricity
and Magnetism
• Moving magnets produce an
electric force.
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• Electric currents and moving
charged particles produce a
magnetic force.
• Result: a moving charged
particle in a magnetic field
will accelerate.
http://img105.imageshack.us/img105/5114/magfield0ct.jpg
Origin of the Pulsing Effect
Motion on a Large Scale Near a
Rotating Magnet
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http://www.atnf.csiro.au/news/press/images/binary_pulsar/
Charged particles
move upward or
downward (depending
on the charge) at the
pulsar’s rotational
poles.
Origin of the Pulsing Effect
Motion in a Magnetic Field
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• A charged particle placed in a
magnetic field will spiral around
the magnetic field lines.
Origin of the Pulsing Effect
Accelerating
A Charged
Particle
• Light is emitted in a
direction perpendicular
to the magnetic field.
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Synchrotron Radiation = Light
Origin of the Pulsing Effect
The
Lighthouse
Effect
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http://www.shatters.net/forum/viewtopic.php?t=11372
Conclusions
• Pulsars are rapidly rotating neutron
stars with powerful magnetic fields.
• A misalignment in the rotational
and magnetic axes leads to the
emission of beams of light from
a pulsar’s magnetic poles.