Rapidly Spinning Compact Stars with Deconfinement Phase Transition

We study rapidly spinning compact stars with equations of state featuring a first order phase transition between strongly coupled nuclear matter and deconfined quark matter by employing the gauge/gravity duality. We consider a family of models, which allow purely hadronic uniformly rotating stars with masses up to approximately $2.9\, \mathrm{M}_\odot$, and are therefore compatible with the interpretation that the secondary component ($2.59^{+0.08}_{-0.09}\, \mathrm{M}_\odot$) in GW190814 is a neutron star. These stars have central densities several times the nuclear saturation density so that strong coupling and non-perturbative effects become crucial. We construct models where the maximal mass of static (rotating) stars $M_{\mathrm{TOV}}$ ($M_{\mathrm{max}}$) is either determined by the secular instability or a phase transition induced collapse. We find largest values for $M_{\mathrm{max}}/M_{\mathrm{TOV}}$ in cases where the phase transition determines $M_{\mathrm{max}}$, which shifts our fit result to $M_{\mathrm{max}}/M_{\mathrm{TOV}} = 1.227^{+0.031}_{-0.016}$, a value slightly above the Breu-Rezzolla bound $1.203^{+0.022}_{-0.022}$ inferred from models without phase transition.