A Pulsar’s Life Continues Melissa Anholm University of Wisconsin, Milwaukee 6 October, 2008.

A Pulsar’s Life A Pulsar’s Life ContinuesContinues

Melissa AnholmMelissa Anholm

University of Wisconsin, MilwaukeeUniversity of Wisconsin, Milwaukee

6 October, 20086 October, 2008

OutlineOutline Initial SlowingInitial Slowing

Energy lost as radio waves.Energy lost as radio waves. Pulsar slows and dims.Pulsar slows and dims.

““Recycling” of PulsarsRecycling” of Pulsars Pulsar steals matter from another starPulsar steals matter from another star Rotation speed is changed Rotation speed is changed X-rays are emitted.X-rays are emitted.

Recycled PulsarsRecycled Pulsars After accretion stops, so do X-rays.After accretion stops, so do X-rays. Original emission mechanism has become active Original emission mechanism has become active

again.again. Predictable timing - useful for experiments.Predictable timing - useful for experiments.

• Speed of Rotation• Strength of Magnetic Field

http://www.shatters.net/forum/viewtopic.php?t=11372

The amount of electromagnetic radiation produced by a pulsar depends on:

Note: Mechanism is still not well-understood.

Pulsar Population

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are needed to see this picture.

Young PulsarsYoung Pulsars

The pulsar’s rotation slows.

The pulsar stops emitting electromagnetic radiation.

Electromagnetic Radiation Carries Energy Away


Pulsar Population



Young PulsarsYoung Pulsars

Pulsars in Binary Systems May Be

Able to Shine Again

Pulsars in Binary Systems May Be

Able to Shine Again

Accretion DiskCompanion Star

Neutron Star http://www.noao.edu/outreach/press/pr08/pr0802.html

Spinning Things Spread Out Spinning Things Spread Out into a Diskinto a Disk



So what happens to the neutron star?

So what happens to the neutron star?

• The stolen matter gives the neutron star a “kick”.

• The neutron star’s rotation speeds up or slows down.

• Rapidly rotating neutron stars can again emit beams of radio waves.

http://www.noao.edu/outreach/press/pr08/pr0802.html

“Recycling”



Infalling Matter Reaches Very Infalling Matter Reaches Very High Speeds before ImpactHigh Speeds before Impact

Stolen matter hits hard and produces heat.

Hot Spots Form on Hot Spots Form on Magnetic PolesMagnetic Poles

Accretion Disk

Hot Spot at Magnetic Pole

Magnetic Field Lines

Axis of Rotation

Flow of Hot Gas

Hot Things GlowHot Things Glow

““Red Hot”Red Hot” ““X-Ray Hot”X-Ray Hot”

Rotating Hot Spots Emit Rotating Hot Spots Emit X-RaysX-Rays

• When the hot spots come into view, we detect a “pulse” ofWhen the hot spots come into view, we detect a “pulse” of X-ray radiation.X-ray radiation.

It’s an X-ray pulsar, now!It’s an X-ray pulsar, now!



http://spacibm.rice.edu/~baring/astr350/astr350_cosmos.html

Two Emission Mechanisms

X-RaysX-Rays Radio WavesRadio Waves• Emission mechanism Emission mechanism depends on infalling matter depends on infalling matter producing hot spots.producing hot spots.

• Hot spots glow--radiation Hot spots glow--radiation is sent in all directions.is sent in all directions.

• We observe pulses when We observe pulses when the hot spots are on the side the hot spots are on the side of the neutron star facing of the neutron star facing us.us.

• Emission mechanism Emission mechanism depends on rotational depends on rotational speed and magnetic field speed and magnetic field strength.strength.

• Radio waves are Radio waves are directed in beams from directed in beams from the magnetic poles.the magnetic poles.

• We observe pulses We observe pulses when the beams are when the beams are directed at usdirected at us



http://spacibm.rice.edu/~baring/astr350/astr350_cosmos.html

X-Ray Pulsars and Radio Pulsars

• X-Ray-emitting hot spots glow in all X-Ray-emitting hot spots glow in all directions. directions. • Radio waves are emitted in beams from Radio waves are emitted in beams from the magnetic poles.the magnetic poles.

For many pulsars, we observe X-rays, For many pulsars, we observe X-rays, but not radio waves, even though we but not radio waves, even though we think they emit both.think they emit both.



Accretion Must Eventually End

• Supernova• Companion shrinks when it exhausts fuel• Companion is completely evaporated• Passing star disrupts orbits

http://upload.wikimedia.org/wikipedia/commons/1/10/Supernova_Companion_Star.jpg



“Recycled” Pulsars• When the accretion process ceases, the hot spots on the neutron star cool.

No more X-rays.

• The neutron star may now be rotating quickly again.

Initial mechanism for producing radio waves has been re-activated.

http://commons.wikimedia.org/wiki/Image:Pulsar_schematic.svg

• Spinning Faster• More Massive


It takes a bigger push to change the rotation speed by a measurable amount.

Pulses are very predictable. Pulses are very predictable. Good for GW detection! Good for GW detection!

What’s so Great about a Recycled Pulsar?

A Pulsar’s Life Continues Melissa Anholm University of Wisconsin, Milwaukee 6 October, 2008.

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