The observational appearance of strange stars

Abstract

Strange quark matter with the density of ~ 5\times 10^{14} g cm^{-3} might exist up to the surface of a strange star. This differs qualitatively from the case of a neutron star and opens observational possibilities to distinguish strange stars from neutron stars. The thermal emission of photons and e^+e^- pairs from the bare (or nearly bare) quark surface of hot strange stars is reviewed. Bare strange stars are reasonable candidates for soft gamma-ray repeaters. The bursting activity of a soft gamma-ray repeater may be explained by fast heating of the bare quark surface of a strange star up to the temperature of ~ (1-2)\times 10^9 K and its subsequent thermal emission.