Photon ring autocorrelations from gravitational fluctuations around a black hole

TL;DR

This paper explores how gravitational fluctuations around black holes influence photon ring autocorrelations, proposing a method to detect these effects using VLBI and gravitational wave techniques, potentially opening new avenues in black hole physics research.

Contribution

It introduces a novel approach to detect gravitational fluctuations around black holes through photon ring autocorrelations using VLBI response functions.

Findings

Correlation shapes differ from stochastic emission sources

Order-of-magnitude estimates for SNR suggest detectability

Sensitivity curves indicate potential for future gravitational fluctuation detection

Abstract

The images of supermassive black holes in M87 and our galaxy captured by the Event Horizon Telescope (EHT) might open up a new way for exploring black hole physics at the horizon scale. Theoretically, this could provide insights into studying the emission sources around a black hole or the geometries of the black hole itself. This paper investigates the two-point correlations of intensity fluctuations on the photon ring, resulting from the existence of shock waves or gravitational fluctuations around a black hole. Following approaches used in the field of gravitational wave detectors, we introduce response functions of very long baseline interferometry (VLBI) for detecting gravitational fluctuations and study the shape of the overlap reduction functions. It is found that the shape of the correlations here differs from that resulting from stochastic emission sources. By providing an order-of-magnitude estimate for the signal-to-noise ratio (SNR), we obtain sensitivity curves for the detection of gravitational fluctuations. This might reveal the potential for detecting gravitational fluctuations with future VLBI observations in the LIGO frequency band.