Black holes waltzing with matter

Black holes waltzing with matter

Black holes rotate, as the vast majority of celestial bodies. But they are not rotating alone. Surrounding every black hole there is matter, typically in the form of dust. Black holes and matter waltz together, each one influencing the other, as described by Einstein's equations of general relativity. The complexity of these equations makes it very difficult to analyze the interaction between black holes and the surrounding matter, especially because of the black hole’s rotation. Thus, until now most studies resorted to computer simulations or to simplified models, for example, by neglecting the influence of the matter on the black hole or the rotation of space-time.

In this paper, we identify a novel scenario in which the full interactions can be addressed in rotating systems, and in this sense constitutes a better approximation to reality. Adopting a mathematical model that considers space-time as having five dimensions -- instead of the usual four -- we were able to treat the interplay between rotating black holes and their surrounding matter with a similar degree of simplicity as in a nonrotating context.This work introduces a framework that can be used in the future to deepen our understanding of realistic black holes.

 

Read the paper: http://inspirehep.net/record/1281676

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Effective action and linear response of compact objects in Newtonian gravity

Effective action and linear response of compact objects in Newtonian gravity

by Sayan Chakrabarti, Térence Delsate and Jan Steinhoff

accepted for publication in Physical Review D, Phys. Rev. D88 (2013) 084038, e-Print: arXiv:1306.5820 [gr-qc] | PDF

Abstract: We apply an effective field theory method for the gravitational interaction of compact stars, developed within the context of general relativity, to Newtonian gravity. In this effective theory a compact object is represented by a point particle possessing generic gravitational multipole moments. The time evolution of the multipoles depends on excitations due to external fields. This can formally be described by a response function of the multipoles to applied fields. The poles of this response correspond to the normal oscillation modes of the star. This gives rise to resonances between modes and tidal forces in binary systems. The connection to the standard formalism for tidal interactions and resonances in Newtonian gravity is worked out. Our approach can be applied to more complicated situations. In particular, a generalization to general relativity is possible.

 

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