Universal relations for fast rotating neutron stars without equation of state bias

We provide a summary of several parametrisations for the nuclear equation of state that have been proposed over the past decades and list viable ranges for their parameters. Based on these parametrisations, we construct a large database of rotating neutron star models, which are arranged in sequences of constant central energy density. After filtering these sequences with respect to generous astrophysical constraints, we discover tight universal relations for various bulk quantities of uniformly rotating neutron stars of arbitrary rotation rates. These universal relations allow to estimate, at very low computational cost, bulk quantities of rotating neutron stars employing mass, radius, and moment of inertia of associated non-rotating neutron stars. The relations are calibrated to a large, model-agnostic dataset, thereby eliminating a potential bias, and prove to be robust. Such relations are important for future, high-precision measurements coming from electromagnetic and gravitational wave observations and may be used in equation of state inference codes or gravitational wave modeling among others.