Dynamics of extended bodies in a Kerr spacetime with spin-induced quadrupole tensor

TL;DR

This paper analyzes how extended bodies with spin and quadrupole moments move in Kerr spacetime, revealing the impact of spin-induced quadrupoles on orbital stability and frequencies.

Contribution

It provides an analytical study of the equatorial motion of spinning extended bodies with quadrupole moments in Kerr spacetime, including ISCO shift calculations.

Findings

Analytical determination of ISCO shift due to spin

Calculation of last circular orbit frequency

Insights into spin-quadrupole effects on orbital dynamics

Abstract

The features of equatorial motion of an extended body in Kerr spacetime are investigated in the framework of the Mathisson-Papapetrou-Dixon model. The body is assumed to stay at quasi-equilibrium and respond instantly to external perturbations. Besides the mass, it is completely determined by its spin, the multipolar expansion being truncated at the quadrupole order, with a spin-induced quadrupole tensor. The study of the radial effective potential allows to analytically determine the ISCO shift due to spin and the associated frequency of the last circular orbit.