Constraining the distribution of dark matter at the Galactic centre using the high-resolution Event Horizon Telescope

TL;DR

This paper explores how the Event Horizon Telescope can constrain dark matter distribution near the Galactic centre by analyzing black hole shadow sizes, highlighting current observational limitations.

Contribution

It introduces a toy model linking dark matter effects to black hole shadow size and discusses potential constraints from EHT observations.

Findings

Dark matter can influence the size of the black hole shadow.

Current observational uncertainties hinder detecting dark matter effects.

Dark matter effects add uncertainty to tests of general relativity.

Abstract

We investigate constraints on the distribution of dark matter in the neighbourhood of the Galactic centre that may eventually be attained with the high-resolution Event Horizon Telescope (EHT). The shadow of a black hole in vacuum is used to generate a toy model describing how dark matter affects the size of the shadow of the supermassive black hole located at the Galactic centre. Observations by the EHT may constrain the properties of the dark matter distribution in a possible density spike around the black hole. Current uncertainties due to both the resolution of the telescope and the analysis of stellar orbits prevent one from discerning the effect of dark matter on the measured size of the shadow. The change in the size of the shadow induced by dark matter can be seen as an additional uncertainty in any test of general relativity that relies on using the angular size of the shadow to estimate the Schwarzschild radius of the black hole.