Within a confining quark matter model which considers phenomenologically the
quark confinement and asymptotic freedom as well as the chiral symmetry
restoration and quark deconfinement at high baryon density, we find that if the
up-down quark matter (udQM) is more stable than nuclear matter and strange
quark matter (SQM), the maximum mass of static quark stars with udQM is
2.77Mββ under agreement with both the constraints on star tidal
deformability from gravitational wave signal GW170817 and the mass-radius of
PSR J0030+045 measured simultaneously by NICER. In contrast, the conventional
strange quark star with SQM has a maximum static mass of only 2.05Mββ
and its radius significantly deviates from NICER's constraint. Our results thus
provide circumstantial evidence suggesting the recently reported GW190814's
secondary component with a mass of 2.59β0.09+0.08βMββ could be an
up-down quark star.Comment: 5 pages, 2 figure