A Metric for Testing the Nature of Black Holes. (arXiv:1210.0483v1 [gr-qc])

A Metric for Testing the Nature of Black Holes. (arXiv:1210.0483v1 [gr-qc]):
In general relativity, astrophysical black holes are uniquely described by
the Kerr metric. Observational tests of the Kerr nature of these compact
objects and, hence, of general relativity, require a metric that encompasses a
broader class of black holes as possible alternatives to the usual Kerr black
holes. Several such Kerr-like metrics have been constructed to date, which
depend on a set of free parameters and which reduce smoothly to the Kerr metric
if all deviations vanish. Many of these metrics, however, are valid only for
small values of the spin or small perturbations of the Kerr metric or contain
regions of space where they are unphysical hampering their ability to properly
model the accretions flows of black holes. In this paper, I describe a
Kerr-like black hole metric that is regular everywhere outside of the event
horizon for black holes with arbitrary spins even for large deviations from the
Kerr metric. This metric, therefore, provides an ideal framework for tests of
the nature of black holes with observations of the emission from their
accretion flows, and I give several examples of such tests across the
electromagnetic spectrum with current and near-future instruments.

Note: This paper notes how broadened Fe-K lines could test the black hole 'No-Hair' Theorem, with predictions of line shapes.