Observational Electromagnetic Signatures of Spinning Black Holes

Abstract

As we enter the era of precision black hole imaging, identifying universal observational signa- tures which of the near horizon strong field region will become increasingly useful in constraining the parameters–mass, spin, spin axis orientations–of the black holes. In this dissertation we de- scribe progress in analytic characterization of such signatures. These arise from two critical phenomena related to the Kerr geometry: the presence of critical null geodesics, and the emer- gent conformal symmetry of the near horizon region of (near-)extremal black holes. We present three such observational signatures for electromagnetic emission: First, we analyt- ically predict the polarized near-horizon emissions for high-spin black holes like M87* and find a distinctive pattern of whorls aligned with the spin. Next, we analyze the maximum observable blueshift of the electromagnetic emission from an equatorial disk of emitters on stable circular equatorial orbits around a Kerr black hole. We find that small values of the maximum blueshift yield an excellent probe of inclination, while larger values provide strong constraints on spin or inclination in terms of the other. Finally, we consider monochromatic and isotropic photon emission from circular equatorial Kerr orbiters. We derive analytic expressions for the photon escape probability and the redshift-dependent total flux collected on the celestial sphere as a function of emission radius and black hole parameters.