Observational features of hot spots on neutron stars with a photon sphere

Abstract

Abstract We describe and illustrate light deflection near neutron stars possessing a photon sphere motivated by modern confirmations of general relativity and its significance for relativistic astrophysics. In this paper, we model the spacetime outside the star with the Schwarzschild metric and summarize the properties of the photon orbits. More especially we illustrate the relativistic appearance of the hot spots on the neutron star surfaces over the celestial screen of an asymptotic observer. We visualize the relativistic images of the neutron star surface for various ratios of neutron star radius to Schwarzschild radius. We establish a noticeable increscent of the visual size of ultra-compact neutron stars with a photon sphere, which could distinguish stars with extremely strong surface gravity with respect to less compact neutron stars. We found an appearance of additional relativistic images of the hot spots leading to a higher magnification of the neutron star luminosity emission regions.