GW170817, general relativistic magnetohydrodynamic simulations, and the neutron star maximum mass

Recent numerical simulations in general relativistic magnetohydrodynamics (GRMHD) provide useful constraints for the interpretation of the GW170817 discovery. Combining the observed data with these simulations leads to a bound on the maximum mass of a cold, spherical neutron star (the TOV limit): <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>M</mml:mi><mml:mo>max</mml:mo><mml:mtext>sph</mml:mtext></mml:msubsup><mml:mo>≲</mml:mo><mml:mn>2.74</mml:mn><mml:mo>/</mml:mo><mml:mi>β</mml:mi></mml:mrow></mml:math> , where <i>β</i> is the ratio of the maximum mass of a uniformly rotating neutron star (the supramassive limit) over the maximum mass of a nonrotating star. Causality arguments allow <i>β</i> to be as high as 1.27, while most realistic candidate equations of state predict <i>β</i> to be closer to 1.2, yielding <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>M</mml:mi><mml:mtext>max</mml:mtext><mml:mtext>sph</mml:mtext></mml:msubsup></mml:mrow></mml:math> in the range 2.16-2.28<i>M</i>_⊙. A minimal set of assumptions based on these simulations distinguishes this analysis from previous ones, but leads a to similar estimate. There are caveats, however, and they are enumerated and discussed. The caveats can be removed by further simulations and analysis to firm up the basic argument.