Physics of pulsars

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Physics of pulsars

• Physics of Neutron Stars
• J. M. Lattimer and M. Prakash
• 23 APRIL 2004 VOL 304 SCIENCE

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Introductions

• Dentist and Smallest stars.
• Combination of nuclear physics, particle physics,
  condense matter physics and astrophysics
• hyperon-dominated matter, de-confined quark
  matter, superfluidity and superconductivity with
  critical temperatures near 1010 k
• Opaqueness to neutrinos, and magnetic fields in
  excess of 1013 Gauss

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Brief History of the discovery

• Chadwicks discovery of the neutron
• The prediction that matter at the almost
  unimaginable density of 1018 kg/m3
• might be formed under gravitational compression
  inside stars was first made by Baade and Zwicky
  in 1934
• Many theoretical approach to the properties of
  the Neutron Stars
• Discovery of 4 pulsars in 1967

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Composition of NS

• A central density nc as high as 5 to 10 times the
  nuclear equilibrium density n0 0.16 fm-3 of
  neutrons and protons found in laboratory nuclei
• Although neutrons dominate the nucleonic
  component, some protons (and enough electrons and
  muons to neutralize the matter) exist
• At supranuclear densities, exotica such as
  strangeness-bearing baryons, condensed mesons
  (pion or kaon) or even deconfined quarks may
  appear.

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SQM Stars

• 1. bare quark-matter surface with a large,
  supranuclear density
• 2. thin layer of normal matter supported by
  Coulomb forces above the quark surface
• up, down, and strange quarks (the charm, bottom,
  and top quarks are too massive to appear inside
  pulsars). Unlike normal stars, SQM stars are
  self-bound, not requiring gravity to hold them
  together.

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How Neutron Stars are Formed

• massive star 8 MT Collapse.
• Type II SNe
• Gravitational binding energy released from a WD
  core to a NS 3GM/5R2 1053 erg, which is about
  10 of its total mass energy Mc2
• The kinetic energy of the expanding remnant 1051
  erg, and the total energy radiated in photons is
  further reduced.
• When n 2 to 3 n0 , a mean free path for
  neutrino is 10 cm, much less than the radius of
  proto-neutron star, 20 km.

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Shock wave

• Core collapse halts when the stars interior
  density reaches n0, which triggers the formation
  of a shock wave at the cores outer edge
• The shock wave propagates only about 100 to 200
  km before it stalls
• Neutrinos resuscitate the shock
• The protoneutron rapidly shrinks because of
  pressure losses from neutrino emission
• The escape of neutrinos occurs on a time scale of
  10 s

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Global Structure of Neutron Stars

• mass-radius (M-R) relation are determined by the
  equations of hydrostatic equilibrium
• TOV and EOS (equation of state)

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Is SAX J1808.4-3658 a Strange Star?(Li et al.
1999)
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A simultaneous measurementof mass and radius
could help to discriminate EOSs
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Difference of EOSs

• GS1, contain large amounts of exotica, any of
  which produces a large amount of softening and
  relatively small radii and maximum masses
• For normal neutron stars, the radius is
  relatively insensitive to the mass in the
  vicinity of 1 to 1.5 MT
• Perhaps two of the most important, but unknown,
  astrophysical quantities are the neutron star
  maximum mass and the radius of 1.4 MJ neutron
  stars

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A simultaneous measurementof mass and radius
could help to discriminate EOSs
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Uncertainties in EOSs

• large variations in predicted radii and maximum
  masses because of the uncertainties in the EOS
  near and above n0
• an important distinction between nuclear and
  neutron star matter is their relative proton
  fraction x

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Layers structure

• Atmosphere plays an important role in shaping
  the photon spectrum
• Envelope crucially influences the transport and
  release of thermal energy from the stars surface
• Crust 1 to 2 km, primarily contains nuclei. at
  densities above the neutron drip density,
  neutrons leak out of nuclei.
• Outer core neutron 3P2 superfluid and the
  protons 1S0 superconductor
• Inner core a mixed phase of hadronic and
  deconfined quark matter, even if strange quark
  matter is not the ultimate ground state of matter

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How to distinguish EOSs?

• The missing information

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The spin up of a pulsar in the binary system

• Accretion phase, accretion extend to the surface
  of the pulsar.

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Variation in the rotation inertia should not be
ignored
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SAX J1808.4-3658
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Her X-1
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2A 1822-371
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application

• A method to determine the EOS of pulsar in binary
  systems.
• Constraint the theoretical particle physics
• Predict the observational timing feature of the
  SQM stars