Surface Electric Field of Bare Strange Stars Accepted by Astro'

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Surface Electric Field of Bare Strange
Stars(Accepted by Astro. Astrophy.)

• Jian Hu
• R. X. Xu
• 3/7/2002

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Introduction

• It is of great importance to identify strange
  stars
• To distinguish NS and BSS according to their
  sharp differences of surface conditions, we study
  the surface properties of BSS in details
• Strong electrical field (1017V/cm) should be at
  the bare quark surface of a strange star because
  of the mass difference of strange quark and up
  (or down) quark
• E could play an important role in producing the
  thermal emission of BSS by the Usov mechanism

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Usov Mechanism

• According to strong field QED, e pairs are
  spontaneously created rapidly in a few empty
  quantum states with energy
• ? lt ?F-2me c2
• e pairs annihilated into photons which are
  thermalized in the electron layer around a BSS
  (optically thick for T gt109K)
• This mechanism has been applied tentatively to
  soft gamma ray repeaters
• This mechanism depends on many parameters, i.e.
  E, ?rE
• In the bag model, E, ?rE are functions of ac, ms,
  B

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What we have done

• We used the bag model and the Thomas-Fermi model,
  improved the calculation of the electric fields
  in the vicinity of BSS surface, considering the
  boundary effect.
• We investigate the electric character of BSSs for
  varying ac, but with typical parameters ms200
  MeV and B1/4145 MeV
• Then calculated the ?rE as the functions of ac,
  ms, B, show the relations in figures.

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Equation I

• Thomas-Fermi model the quarks and electrons keep
  chemical equilibrium locally, and the relation
  between charge density and electric potential is
  described by the classical Poisson equation
• The chemical potential µ can be determined by the
  condition that the pressure on the quark surface
  is zero, Pz00.
• The kinetic energy of electrons is equal to the
  electric potential, pe V
• Electron number density, neV3/3p2

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Equation II
Boundary conditions
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Results
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Electric potential as the function of z
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Electric field decreases above the quark surface.
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Electric field decreases sharply below the quark
surface.
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A set of calculated thickness ?rE, as a function
of bag parameter B and ms
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Conclusion Discussion

• Usov mechanism can work for bag parameters within
  rather wide range
• strong electric field resides only about 10 fm
  below the quark surface
• E is an exponential function of z below the quark
  surface

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Thanks!