Event Horizon Telescope Observations as Probes for Quantum Structure of Astrophysical Black Holes
Steven B. Giddings and Dimitrios Psaltis
Abstract (click to read)
For more information on this work, read the paper submitted to Physical Review D. In this web page, you can find some useful animations, the stills of which appear as figures in the paper.
The discovery of Hawking radiation yields a logical contradiction when one tries to account for quantum information absorbed by a black hole: this information can’t escape, can’t be destroyed, and can’t be preserved after the black hole evaporates. This situation appears to represent a fundamental conflict between the principles underpinning local quantum field theory: the principles of quantum mechanics, relativity, and locality. Therefore, while it has long been believed that the vicinity of the horizon is well-described by classical general relativity, since curvatures are expected to be small there, many theorists who study quantum evolution of black holes have now concluded that there must be modifications to their description via local quantum field theory, and that in order to resolve the conflict, these modifications must extend at least to horizon scales. A natural candidate for these yields “soft” quantum deformations of the effective metric near a black hole.
In the near future two new approaches to probing the innermost regions of black hole spacetimes will become available, with the potential of offering probes of their quantum structure that are clean of astrophysical complexities. The first involves gravitational wave observations either of coalescing black holes (such as the initial LIGO detection of the source GW150914) or of extreme mass ratio inspirals. The second involves obtaining images of accreting black holes with horizon-scale resolution using the Event Horizon Telescope. The goal of our work is to investigate the possible signatures of soft quantum modifications to black hole metrics that could be imprinted on Event Horizon Telescope observations, and thus the sensitivity of these observations to such effects.
As a first step, we performed a number of exploratory calculations of the effect on photon trajectories of different monochromatic perturbations of the black-hole metric in order to identify the range of parameters that will introduce observable effects on the predicted images.
We then used a simple model for the plasma in the accretion flow around a black hole in order to make concrete predictions of the effects of strong, soft quantum perturbations on the image of accreting black holes.