Understand
We demonstrate that the observation of old strange quark stars (SQSs) can set important limits on the scattering cross sections $\sigma_q$ between the light quarks and the non-interacting scalar dark matter (DM).
- By analyzing a set of 1403 of solitary pulsarlike compact stars in the Milky Way, we find the old solitary pulsar PSR J1801-0857D can set the most stringent upper limits on $\sigma_q$ or the DM-proton scattering cross sections $\sigma_p$.
- By converting $\sigma_q$ into $\sigma_p$ based on effective operator analyses, we show the resulting $\sigma_p$ limit by assuming PSR J1801-0857D to be a SQS could be comparable with that of the current direct detection experiments but much weaker (by several orders of magnitude) than that obtained by assuming PSR J1801-0857D to be a neutron star (NS), which requires an extremely small $\sigma_p$ far beyond the limits of direct detection experiments.
- Our findings imply that the old pulsars are favored to be SQSs rather than NSs if the scalar DM were observed by future terrestrial experiments.