Nuclear Physics Multimessenger Astrophysics Constraints on the Neutron Star Equation of State: Adding NICER's PSR J0740+6620 Measurement
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Abstract
In the past few years, new observations of neutron stars and neutron-star\nmergers have provided a wealth of data that allow one to constrain the equation\nof state of nuclear matter at densities above nuclear saturation density.\nHowever, most observations were based on neutron stars with masses of about 1.4\nsolar masses, probing densities up to $\\sim$ 3-4 times the nuclear saturation\ndensity. Even higher densities are probed inside massive neutron stars such as\nPSR J0740+6620. Very recently, new radio observations provided an update to the\nmass estimate for PSR J0740+6620 and X-ray observations by the NICER and XMM\ntelescopes constrained its radius. Based on these new measurements, we revisit\nour previous nuclear-physics multi-messenger astrophysics constraints and\nderive updated constraints on the equation of state describing the neutron-star\ninterior. By combining astrophysical observations of two radio pulsars, two\nNICER measurements, the two gravitational-wave detections GW170817 and\nGW190425, detailed modeling of the kilonova AT2017gfo, as well as the gamma-ray\nburst GRB170817A, we are able to estimate the radius of a typical 1.4-solar\nmass neutron star to be $11.94^{+0.76}_{-0.87} \\rm{km}$ at $90\\%$ confidence.\nOur analysis allows us to revisit the upper bound on the maximum mass of\nneutron stars and disfavors the presence of a strong first-order phase\ntransition from nuclear matter to exotic forms of matter, such as quark matter,\ninside neutron stars.\n