Surface Photon Emissivity of Bare Strange Stars

We consider the bremsstrahlung surface photon emissivity of strange quarkstars, by sistematically taking into account the effects of the multiplescatterings of the highly relativistic quarks in a dense medium (theLandau-Pomeranchuk-Migdal effect). Due to interference between amplitudes ofnearby interactions, the bremsstrahlung emissivity from strange star surface issuppressed for frequencies smaller than a critical frequency. The range of thesuppressed frequencies is a function of the quark matter density at the star'ssurface and of the QCD coupling constant. For temperatures much smaller thanthe Fermi energy of the quarks the bremsstrahlung spectrum has the sametemperature dependence as the equilibrium black body radiation. Multiplecollisions could reduce the intensity of the bremsstrahlung radiation by anorder of magnitude. The effect of the thin electron layer at the surface of thequark star on the bremsstrahlung spectrum is also analyzed in detail. It isshown that absorption in the semi-degenerate electron gas can alsosignificantly reduce the intensity of the quark-quark bremsstrahlung radiationand, consequently, the surface emissivity. Hence the combined effects ofmultiple collisions and absorption in the electron layer could make the softphoton surface radiation of quark stars six orders of magnitude smaller thanthe equilibrium black body radiation.Comment: 36 pages, 10 figures, to appear in Ap