Low-Mass X-Ray Binaries with Strange Quark Stars

Strange quark stars (SSs) may originate from accreting neutron stars (NSs) in low-mass X-ray binaries (LMXBs). Assuming that conversion of NS matter to SSs occurs when the core density of accreting NS reaches the density of quark deconfinement, ∼5ρ0, where ρ0 ∼ 2.7 × 1014 g cm-3 is nuclear saturation density, we investigate LMXBs with SSs (qLMXBs). In our simulations, about 0.1–10% of LMXBs can produce SSs, which greatly depends on the masses of nascent NSs and the fraction of transferred matter accreted by the NSs. If the conversion does not affect binary systems, LMXBs evolve into qLMXBs. We find that some observational properties (spin periods, X-ray luminosities and orbital periods) of qLMXBs are similar to those of LMXBs, and it is difficult to differentiate between them. If the conversion disturbs the binary systems, LMXBs can produce isolated SSs. These isolated SSs could be submillisecond pulsars, and their birthrate in the Galaxy is ∼5–70 Myr-1.