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Abstract

We investigate the quark star equation of state within the Bayesian
statistical approach using the widely-used bag model, assuming the strange
quark matter is in the color-flavor locked phase. Three types of filters are
employed for the posterior distribution: Normal atomic nuclei should not decay
into nonstrange quark matter, bulk strange quark matter should be more stable
than the most bound atomic nuclei, and the lower limit on the maximum mass
$M_{\rm TOV}$. The likelihood functions incorporate observational constraints
from the tidal deformability measurement of the GW170817 binary merger by
LIGO/Virgo and the measurements of PSR J0030+0451's mass and radius by NICER.
The $90\%$ posterior credible boundary around the most probable values of the
quark star maximum mass is found to be $M_{\rm TOV}=2.15_{-0.12}^{+0.16}
M_{\odot}$, with the radius and tidal deformability of a canonical $1.4
M_{\odot}$ star being $R_{\rm 1.4}=11.52_{-0.46}^{+0.51}\,{\rm km}$ and
$\Lambda_{\rm 1.4}=670_{-160}^{+230}$, respectively. Nevertheless, the color
superconductivity gap is poorly constrained by those observed global star
properties, and no clear evidence about the sound speed behavior in strange
quark matter is manifested. A possible probe of the quark pairing gap through
future tidal deformability measurement of massive quark stars (close to $M_{\rm
TOV}$) is also discussed.