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Neutron Stars

0. Neutron Stars . 0. Gradual compression of a stellar iron core. Radial Structure of a Neutron Star. - Heavy Nuclei ( 56 Fe). - Heavy Nuclei ( 118 Kr); free neutrons; relativistic, degenerate e -. - Superfluid neutrons. 0. Properties of Neutron Stars. Typical size: R ~ 10 km.

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Neutron Stars

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  1. 0 Neutron Stars

  2. 0 Gradual compression of a stellar iron core

  3. Radial Structure of a Neutron Star - Heavy Nuclei (56Fe) - Heavy Nuclei (118Kr); free neutrons; relativistic, degenerate e- - Superfluid neutrons

  4. 0 Properties of Neutron Stars Typical size: R ~ 10 km Mass: M ~ 1.4 – 3 Msun Density: r ~ 4x1014 g/cm3 → 1 teaspoon full of NS matterhas a mass of ~ 2 billion tons!!! Rotation periods: ~ a few ms – a few s Magnetic fields: B ~ 108 – 1015 G (Atoll sources; ms pulsars) (magnetars)

  5. 0 Neutron Star Cooling Tc ~ 1011 K n → p + e- + ne p + e- → n + ne (non-degenerate n, p) ~ 1 d URCA process: Tc ~ 109 K ~ 1,000 yr neutrino cooling Tc ~ 108 K Lph ~ 7x1032 erg/s lmax ~ 30 Å (soft X-rays) Tc ~ 108 K; Teff ~ 106 K for ~ 10,000 yr

  6. 0 The Lighthouse Model of Pulsars A Pulsar’s magnetic field has a dipole structure, just like Earth. Radiation is emitted mostly along the magnetic poles. Rapid rotation along axis not aligned with magnetic field axis → Light house model of pulsars Pulses are not perfectly regular → gradual build-up of average pulse profiles

  7. 0 Pulsar Emission Models:Polar Cap model Particle acceleration along magnetic field lines Synchrotron emission Curvature radiation Pair production Electromagnetic cascades

  8. Pulsar Emission Models:Outer Gap model W Electrons are bound to magnetic fields co-rotating with the pulsar At a radial distance r = c/W co-rotation at the speed of light → “light cylinder” → Particles ripped off magnetic fields Synchrotron emission Curvature radiation Light Cylinder

  9. 0 Pulsar periods and derivatives Associated with supernova remnants Mostly in binary systems

  10. 0 Pulsar periods Over time, pulsars lose energy and angular momentum => Pulsar rotation is gradually slowing down. dP/dt ~ 10-15 Pulsar Glitches: DP/P ~ 10-7 – 10-8

  11. 0 Energy Loss of Pulsars From the gradual spin-down of pulsars: d dE/dt = (½ I w2) = I w w = - (1/6) m┴2w4 r4 c-3 dt m┴ ~ B0 r sin a One can estimate the magnetic field of a pulsar as B0 ≈ 3 x 1019√PP G

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  14. 0 Images of Pulsars and other Neutron Stars The vela Pulsar moving through interstellar space The Crab nebula and pulsar

  15. 0 The Crab Pulsar Pulsar wind + jets Remnant of a supernova observed in A.D. 1054

  16. 0 The Crab Pulsar Visual image X-ray image

  17. 0 Dispersion of Pulsar Signals dt = (4pe2/mecw13) dw DM d DM = ∫ ne(s) ds 0 DM = Dispersion Measure

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