Neutron star event horizons

Abstract

New physical evidence of the compressibility of neutrons has supported a reappraisal of how neutron stars transition into black holes, taken from the perspective of an internal observer. After comparing observational evidence with relativistic models, it is concluded that, at least nonrotating isolated black holes are better termed as black stars, which fit a continuum of increasingly massive neutron stars that become invisible once they exceed a critical mass, suggested as 5 M⊙. Beyond this mass, two event horizons develop concurrently, separating to form a photon trap that exists between the inner horizon and the outer horizon. This inner horizon (below the surface) avoids the formation of a real singularity and is apparently ≤ 6.75 km radius, while the outer horizon is ≥ 6.75 km radius, confirmed as 50% of the Schwarzschild radius. The mathematical singularity that is apparent to an external observer in general relativity may be an illusion. Our methodology also shows how gravitational redshift may inform the mass and surface radius of a neutron star.