arXiv subjects

Pritam Banerjee

Publications and source records attributed to Pritam Banerjee.

22 records · Page 2Linked to original sources

arXiv2019

Tidal effects away from the equatorial plane in Kerr backgrounds

We study tidal effects on self-gravitating Newtonian stars rotating around a Kerr black hole in stable circular orbits away from the equatorial plane. Such cases are exemplified by a non-vanishing Carter's constant. Here, we calculate the tidal disruption limit (Roche limit) of the star numerically, in Fermi normal coordinates. The Roche limit is found to depend strongly on the choice of the orbit, and differs significantly from the equatorial plane result as one approaches nearly polar orbits. As expected, this difference is large when the star is close to the black hole (near to the innermost stable circular orbit) and becomes smaller when the star is far from it. We also discuss the dependence of the Roche limit on the equation of state of the star, taking two specific parameter values as examples.

gr-qc↗

arXiv2018

A novel gravitational lensing feature by wormholes

Horizonless compact objects with light rings (or photon spheres) are becoming increasingly popular in recent years for several reasons. In this paper, we show that a horizonless object such as a wormhole of Morris-Thorne type can have two photon spheres. In particular, we show that, in addition to the one present outside a wormhole throat, the throat can itself act as an effective photon sphere. Such wormholes exhibit two sets of relativistic Einstein ring systems formed due to strong gravitational lensing. We consider a previously obtained wormhole solution as a specific example. If such type of wormhole casts a shadow at all, then the inner set of the relativistic Einstein rings will form the outer bright edge of the shadow. Such a novel lensing feature might serve as a distinguishing feature between wormholes and other celestial objects as far as gravitational lensing is concerned.

gr-qc↗

arXiv2018

On Strong Gravitational Lensing in Rotating Galactic Space-times

We study strong gravitational lensing in rotating space-times which can be thought of as realistic galactic models in General Relativity. To this end, using the Newman-Janis algorithm, we first obtain a rotating version of a static galactic metric advanced by Bharadwaj and Kar. This is matched with a generic external Kerr solution without a slowly-rotating approximation. Next, we construct a rotating version of Perlick's Bertrand space-times and establish this as a new rotating solution of Einstein's equations where each spatial radius admits a stable circular orbit. A rotating generalization of a strong lensing formalism due to Perlick is then applied to the rotating Bharadwaj-Kar metric and the differences with lensing in the purely Kerr background (for a Kerr black hole at the galactic center) is pointed out. Then, arguing that a rotating Bertrand space-time might be a realistic galactic model away from the galactic center, strong lensing is studied in this situation where the central singularity is naked. Possible observational signatures are elaborated upon, which might be useful in distinguishing black holes from naked singularities.

gr-qc↗

arXiv2017

Massless fermions in null Fermi coordinates and an application to analog gravity in $\text{He}^3$-A

Bogoliubov quasiparticles moving in the background of superfluid $\text{He}^3$-A see an apparently curved space-time metric when the background superfluid vacuum is in motion. We study how this curvature couples with the spins of the effectively massless quasiparticles. First, we set up the problem in null Fermi coordinates for radial as well as circular geodesics and then use it in the context of the analog metric seen by the quasiparticles. We obtain an effective magnetic interaction due to curvature coupling, and provide numerical estimates. Some possible implications of these results are then pointed out.

gr-qc↗