55 research outputs found
Trapping of null geodesics in slowly rotating spacetimes
Extremely compact objects containing a region of trapped null geodesics could
be of astrophysical relevance due to trapping of neutrinos with consequent
impact on cooling processes or trapping of gravitational waves. These objects
have previously been studied under the assumption of spherical symmetry. In the
present paper, we consider a simple generalization by studying trapping of null
geodesics in the framework of the Hartle-Thorne slow-rotation approximation
taken to first order in the angular velocity, and considering a uniform-density
object with uniform emissivity for the null geodesics. We calculate effective
potentials and escape cones for the null geodesics and how they depend on the
parameters of the spacetimes, and also calculate the "local" and "global"
coefficients of efficiency for the trapping. We demonstrate that due to the
rotation the trapping efficiency is different for co-rotating and retrograde
null geodesics, and that trapping can occur even for , contrary to
what happens in the absence of rotation
- …