Low-mass X-ray Binaries with Strange Quark Stars

TL;DR

This paper explores the formation of strange quark stars from low-mass X-ray binaries, analyzing their properties, evolution, and potential observational signatures, including the possibility of isolated submillisecond pulsars.

Contribution

It introduces a model for the conversion of neutron stars to strange quark stars in LMXBs and predicts their observable characteristics and birthrates.

Findings

Approximately 1% to 10% of LMXBs can produce SSs.

Converted SSs may be indistinguishable from LMXBs observationally.

Isolated SSs could be submillisecond pulsars with a birthrate of 5-70 per million years.

Abstract

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 to the density of quark deconfinement, $\sim 5 \rho_0$, where $\rho_0\sim 2.7\times 10^{14}$g cm$^{-3}$ is nuclear saturation density, we investigate LMXBs with SSs (qLMXBs). In our simulations, about 1\permil --- 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 binaries systems, LMXBs evolve into qLMXBs. We find that some observational properties (spin periods, X-ray luminosities and orbital periods) of qLMXBs are similar with those of LMXBs, and it is difficult to differ them. If the conversion disturbs the binaries systems, LMXBs can produce isolated SSs. These isolated SSs could be submillisecond pulsars, and their birthrate in the Galaxy is $\sim$5--70 per Myr.