Speaker: Jorge Delgado (CIDMA, University of Aveiro)

GTA group Seminar

Title: Structure of Circular Orbits for Generic Ultracompact Objects

Abstract: "Recently, it has been shown that the radial stability of a light-ring (LR) in a spacetime generated by a stationary, axisymmetric, asymptotically flat object with a Z2 symmetry determines the possibility and radial stability of timelike circular orbits (TCOs) around the LR. In this seminar, I shall revise the previously mentioned result and I shall generalise it by also considering the vertical (angular) stability of the orbits through the study of the radial and vertical epicyclic frequencies. I will show that the vertical stability of the LR only determines the vertical stability of the TCOs around it. A relation between the sum of the squared epicyclic frequencies and the Ricci tensor will also be provided. With such relation, I will show that objects with radially and vertically unstable LRs (TCOs) violate the null (strong) energy condition. If time allows, I shall apply these results to extreme mass ratio inspirals."

Webinar on the 1st of February, via Zoom through the following link:

https://videoconf-colibri.zoom.us/j/91991322136?pwd=V05MVWpNWlFuQTYxR0pMdGJ3bXV5dz09

Passcode: 498547