Multimessenger constraints for ultra-dense matter

Understand

Recent rapid progress in neutron-star (NS) observations offers great potential to constrain the properties of strongly interacting matter under the most extreme conditions.

• In order to fully exploit the current observational inputs and to study the impact of future observations of NS masses, radii, and tidal deformabilities, we analyze a large ensemble of randomly generated viable NS-matter equations of state (EoSs) and the corresponding rotating stellar structures.
• We discuss the compatibility and impact of various hypotheses and measurements on the EoS, including those involving the merger product of the gravitational-wave (GW) event GW170817, the binary merger components in GW190814, and radius measurements of the pulsar PSR J0740+6620.
• We obtain an upper limit for the dimensionless spin of a rigidly rotating NS, $|\chi| < 0.81$, an upper limit for the compactness of a NS, $GM/(Rc^2) < 0.33$, and find that the conservative hypothesis that the remnant in GW170817 ultimately collapsed to a black hole strongly constrains the EoS and the maximal mass of NSs, implying $M_\text{TOV} < 2.53 M_\odot$ (or $M_\text{TOV} < 2.19 M_\odot$ if we assume that a hypermassive NS was created).