Rotational effects in quark stars: comparing different models

Abstract

We investigate the rotational properties of self-bound strange quark stars using two representative quark matter equations of state (EOS): the vector MIT bag model and the density-dependent quark mass (DDQM) model. Through general-relativistic calculations of uniformly rotating sequences, we analyze their mass--radius relations, moments of inertia, quadrupole moments, surface redshifts, Keplerian frequencies, and energy components. A central result of this work is the full decomposition of the stellar energy budget in rotating strange stars, separating gravitational, internal, rotational, and binding energy contributions. Rotation amplifies the intrinsic EOS differences: the MIT model supports more massive ($M_{\max} \gtrsim 3.3\,M_\odot$) compact stars with larger moments of inertia and greater resistance to deformation, while the DDQM model produces larger radii, less massive stars limited by mass-shedding at lower frequencies. Combined measurements of mass, radius, and frequency can thus break the EOS degeneracy; massive, rapidly rotating pulsars favors MIT-like EOS, whereas larger radii in canonical stars point to a DDQM-like model. These rotational observables, soon to be tightly constrained by NICER and next-generation gravitational-wave detectors, offer a means to test the existence and composition of self-bound quark matter in compact stars.