Distinguishing gravitational and emission physics in black-hole imaging: spherical symmetry

Abstract

Imaging a supermassive black hole and extracting physical information requires good knowledge of both the gravitational and the astrophysical conditions near the black hole. When the geometrical properties of the black hole are well understood, extracting information on the emission properties is possible. Similarly, when the emission properties are well understood, extracting information on the black-hole geometry is possible. At present however, uncertainties are present both in the geometry and in the emission, and this inevitably leads to degeneracies in the interpretation of the observations. We explore here the impact of varying geometry and emission coefficient when modelling the imaging of a spherically-accreting black hole. Adopting the Rezzolla-Zhidenko parametric metric to model arbitrary static black-holes, we first demonstrate how shadow-size measurements leave degeneracies in the multidimensional space of metric-deviation parameters, even in the limit of infinite-precision measurements. Then, at finite precision, we show that these degenerate regions can be constrained when multiple pieces of information, such as the shadow-size and the peak image intensity contrast, are combined. Such degeneracies can potentially be eliminated with measurements at increased angular-resolution and flux-sensitivity. While our approach is restricted to spherical symmetry and hence idealised, we expect our results to hold also when more complex geometries and emission processes are considered.

Theory-agnostic Reconstruction of Potential and Couplings from Quasi-Normal Modes

“…Indeed, the latter have been the object of several recent studies to constrain possible deviations of the BH geometry from GR, e.g. [34,[55][56][57][58][59].…”

Multi-level images around Kerr–Newman black holes

“…While the observed profile depends on the less-understood plasma physics in the accretion disk as well, the light bending effect is mainly determined by the spacetime geometry. Thus, the characteristics of the multi-level lensed images may offer us a promising way to test the strong gravity [23][24][25][26][27][28][29][30][31][32][33][34][35].…”

Multi-level images around Kerr-Newman black holes

“…While the observed profile depends on the less-understood plasma physics in the accretion disk as well, the light bending effect is mainly determined by the spacetime geometry. Thus, the characteristics of the multi-level lensed images may offer us a promising way to test the strong gravity [21][22][23][24][25][26][27][28][29][30][31].…”