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A Pulsar’s Life Continues

A Pulsar’s Life Continues. Melissa Anholm University of Wisconsin, Milwaukee 6 October, 2008. Outline. Initial Slowing Energy lost as radio waves. Pulsar slows and dims. “Recycling” of Pulsars Pulsar steals matter from another star Rotation speed is changed X-rays are emitted.

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A Pulsar’s Life Continues

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

  2. Outline • Initial Slowing • Energy lost as radio waves. • Pulsar slows and dims. • “Recycling” of Pulsars • Pulsar steals matter from another star • Rotation speed is changed • X-rays are emitted. • Recycled Pulsars • After accretion stops, so do X-rays. • Original emission mechanism has become active again. • Predictable timing - useful for experiments.

  3. The amount of electromagnetic radiation produced by a pulsar depends on: • Speed of Rotation • Strength of Magnetic Field Note: Mechanism is still not well-understood. http://www.shatters.net/forum/viewtopic.php?t=11372

  4. Pulsar Population Young Pulsars

  5. Electromagnetic Radiation Carries Energy Away The pulsar’s rotation slows. The pulsar stops emitting electromagnetic radiation. http://www.shatters.net/forum/viewtopic.php?t=11372

  6. Pulsar Population Young Pulsars

  7. Pulsars in Binary Systems May Be Able to Shine Again Pulsars in Binary Systems May Be Able to Shine Again Companion Star Neutron Star Accretion Disk http://www.noao.edu/outreach/press/pr08/pr0802.html

  8. Spinning Things Spread Out into a Disk

  9. So what happens to the neutron star? So what happens to the neutron star? “Recycling” • 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

  10. Infalling Matter Reaches Very High Speeds before Impact Stolen matter hits hard and produces heat.

  11. Hot Spots Form on Magnetic Poles Axis of Rotation Accretion Disk Hot Spot at Magnetic Pole Flow of Hot Gas Magnetic Field Lines

  12. Hot Things Glow “Red Hot” “X-Ray Hot”

  13. Rotating Hot Spots Emit X-Rays • When the hot spots come into view, we detect a “pulse” of • X-ray radiation. It’s an X-ray pulsar, now!

  14. Two Emission Mechanisms X-Rays Radio Waves • Emission mechanism depends on rotational speed and magnetic field strength. • Radio waves are directed in beams from the magnetic poles. • We observe pulses when the beams are directed at us • Emission mechanism depends on infalling matter producing hot spots. • Hot spots glow--radiation is sent in all directions. • We observe pulses when the hot spots are on the side of the neutron star facing us. http://spacibm.rice.edu/~baring/astr350/astr350_cosmos.html

  15. X-Ray Pulsars and Radio Pulsars • X-Ray-emitting hot spots glow in all • directions. • Radio waves are emitted in beams from • the magnetic poles. For many pulsars, we observe X-rays, but not radio waves, even though we think they emit both. http://spacibm.rice.edu/~baring/astr350/astr350_cosmos.html

  16. 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

  17. “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

  18. What’s so Great about a Recycled Pulsar? • Spinning Faster • More Massive It takes a bigger push to change the rotation speed by a measurable amount. Pulses are very predictable. Good for GW detection! http://www.shatters.net/forum/viewtopic.php?t=11372

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