  In recent years our understanding of the dense matter equation of state (EOS)
of neutron stars has significantly improved by analyzing multimessenger data
from radio/X-ray pulsars, gravitational wave events, and from nuclear physics
constraints. Here we study the additional impact on the EOS from the jointly
estimated mass and radius of PSR J0740+6620, presented in Riley et al. (2021)
by analyzing a combined dataset from X-ray telescopes NICER and XMM-Newton. We
employ two different high-density EOS parameterizations: a piecewise-polytropic
(PP) model and a model based on the speed of sound in a neutron star (CS). At
nuclear densities these are connected to microscopic calculations of neutron
matter based on chiral effective field theory interactions. In addition to the
new NICER data for this heavy neutron star, we separately study constraints
from the radio timing mass measurement of PSR J0740+6620, the gravitational
wave events of binary neutron stars GW190425 and GW170817, and for the latter
the associated kilonova AT2017gfo. By combining all these, and the NICER
mass-radius estimate of PSR J0030+0451 we find the radius of a 1.4 solar mass
neutron star to be constrained to the 95% credible ranges 12.33^{+0.76}_{-0.81}
km (PP model) and 12.18^{+0.56}_{-0.79} km (CS model). In addition, we explore
different chiral effective field theory calculations and show that the new
NICER results provide tight constraints for the pressure of neutron star matter
at around twice saturation density, which shows the power of these observations
to constrain dense matter interactions at intermediate densities.
