Symmetry Energy of Strange Quark Matter and Tidal Deformability of Strange Quark Stars

Research performed during the past decade revealed an important role of symmetry energy in the equation of state (EOS) of strange quark matter (SQM). By introducing an isospin-dependent term into the quark mass scaling, the SQM stability window in the equivparticle model was studied. The results show that a sufficiently strong isospin dependence C I can significantly widen the SQM region of absolute stability, yielding results that simultaneously satisfy the constraints of the astrophysical observations of PSR J1614-2230 with 1.928 ± 0.017 M_⊙ and tidal deformability 70 ≤Λ _1.4≤ 580 measured in the event GW170817. With increasing C I , the difference between the u , d , and s quark fractions for the SQM in β - equilibrium becomes inconspicuous for C>0 , leading to small isospin asymmetry δ , and further resulting in similar EOS and structures of strange quark stars (SQSs). Moreover, unlike the behavior of the maximum mass of u - d QSs, which varies with C I depending on the sign of the parameter C , the maximum mass of the SQSs decreases monotonously with increasing C I .