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After the Supernova:After the Supernova:PulsarsPulsarsAfter the Supernova:After the Supernova:PulsarsPulsars

Melissa AnholmMelissa Anholm

University of Wisconsin-MilwaukeeUniversity of Wisconsin-Milwaukee

29 September, 200829 September, 2008

OutlineOutlineOutlineOutline

• Properties of Neutron Stars• Large Magnetic Field

• Rapid Rotation

• Origin of the Pulsing Effect• Motion in a Magnetic Field

• Light Emission

• The Lighthouse Effect

A Typical A Typical Neutron StarNeutron StarA Typical A Typical Neutron StarNeutron Star

• Strong Magnetic FieldStrong Magnetic Field

• Fast RotationFast Rotation

Properties of Neutron StarsProperties of Neutron Stars

Why does it spin so fast?Why does it spin so fast?Why does it spin so fast?Why does it spin so fast?

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A typical young pulsar completes about one rotation per second.

Properties of Neutron StarsProperties of Neutron Stars

A typical star completes about one rotation every week - month.

Magnetic Fields - Now with Magnetic Fields - Now with Lines!Lines!Magnetic Fields - Now with Magnetic Fields - Now with Lines!Lines!

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http://www.freewebs.com/ayxl/magnet.jpeg http://www.utm.edu/staff/cerkal/magnetic_files/image004.jpg

Properties of Neutron StarsProperties of Neutron Stars

After the Collapse: Rotation and the Magnetic Field

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• Dense magnetic field lines Strong magnetic field

• Angular momentum conserved Fast rotation

• Magnetic and rotationalaxes may not be aligned.

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Properties of Neutron Stars

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Misalignment of Magnetic and Rotational Axes - Why We Care

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 LightProperties of Light

Origin of the Pulsing Effect

• “photon” = a particle of light• accelerating charged particles produce photons (!)

QuickTime™ and a decompressor

are needed to see this picture.• Moving magnets produce an electric force.

• Electric currents and moving charged particles produce a magnetic force.

A Strange Connection A Strange Connection between Electricity between Electricity and Magnetismand Magnetism

http://img105.imageshack.us/img105/5114/magfield0ct.jpg

Origin of the Pulsing Effect

• Result: a moving charged particle in a magnetic field will accelerate.

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Motion on a Large Scale Near a Rotating Magnet

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 FieldMotion 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 Accelerating A Charged A Charged

ParticleParticle QuickTime™ and a decompressor

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Synchrotron Radiation = Light

• Light is emitted in a direction perpendicular to the magnetic field.

Origin of the Pulsing Effect

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The The Lighthouse Lighthouse EffectEffect

The The Lighthouse Lighthouse EffectEffect

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Origin of the Pulsing Effect

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.

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