On the Maximum Mass of Neutron Stars and GW190814

Motivated by the recent discovery of a compact object with mass in the range $2.5{-}2.67\, \mathrm{M}_\odot$ in the binary merger GW190814, we revisit the question of the maximum mass of neutron stars (NSs). We use a Markov Chain Monte Carlo approach to generate about 2 million phenomenological equations of state with and without first order phase transitions. We fix the crust equation of state and only assume causality at higher densities. We derive strict upper bounds on the maximum mass of NSs that depend on bulk properties of NSs, such as the radii and the tidal deformabilities of reference NSs. We find that the presence of a NS in GW190814 is not inconsistent with present astronomical constraints on the NS equation of state, but could be ruled out with near-future NICER and/or LIGO/Virgo observations.