Direct astrophysical tests of chiral effective field theory at supranuclear densities

Neutron stars (NSs) contain the densest matter in the universe, and the pressure at densities between 1--3 times nuclear density ($2.8\ifmmode\times\else\texttimes\fi{}{10}^{14}$ g/cm${}^{3}$) determines the relationship between their macroscopic properties, such as mass and radius. The authors compare NS observations from gravitational-wave, X-ray, and radio observations with state-of-the-art theoretical predictions for nuclear forces from chiral effective field theory ($\ensuremath{\chi}$EFT) to determine its validity at high density and when it might break down. The combination of astrophysical observations and $\ensuremath{\chi}$EFT predictions improves the constraints on NS radii and the pressure of dense matter in the NS core. These constraints provide new insights about the phase diagram of dense matter at low temperature and the role of many-body nuclear forces at work within NS cores.