Multi-messenger constraints on the neutron-star equation of state and
  the Hubble constant
  Observations of neutron-star mergers based on distinct messengers, including
gravitational waves and electromagnetic signals, can be used to study the
behavior of matter denser than an atomic nucleus, and to measure the expansion
rate of the Universe described by the Hubble constant. We perform a joint
analysis of the gravitational-wave signal GW170817 with its electromagnetic
counterparts AT2017gfo and GRB170817A, and the gravitational-wave signal
GW190425, both originating from neutron-star mergers. We combine these with
previous measurements of pulsars using X-ray and radio observations, and
nuclear-theory computations using chiral effective field theory to constrain
the neutron-star equation of state. We find that the radius of a $1.4$ solar
mass neutron star is $11.75^{+0.86}_{-0.81}\ \rm km$ at $90\%$ confidence and
the Hubble constant is $66.2^{+4.4}_{-4.2}\ \rm km \,Mpc^{-1}\, s^{-1}$ at
$1\sigma$ uncertainty.
