Neutron Stars and Gravitational Wave Observation of Strong-field Gravity

In the context of scalar-tensor gravity theories, the apparent mass of neutron stars as seen from an observer at infinity is numerically calculable but requires careful matching, first at the star’s edge, between interior and exterior solutions, none of them being totally Schwarzschild-like but presenting instead small oscillations of the curvature scalar R ; and second at large radii, where the Newtonian potential is used to identify the mass of the neutron star. Thus, for the same equation of state, this mass definition is always larger than its general relativistic counterpart and consequently, star radii are in general smaller than in General Relativity, which can give an observational handle on such classes of models at the astrophysical level. Finally, because neutron stars masses can be much larger than General Relativity counterparts, the total energy available for radiating gravitational waves could be of order several solar masses, and thus a merger of these stars constitutes an interesting wave source.