How Spatially Resolved Polarimetry Informs Black Hole Accretion Flow Models

Angelo Ricarte, Michael D. Johnson, Yuri Y. Kovalev, Daniel C. M. Palumbo, Razieh Emami

Submitted on 7 November 2022


The Event Horizon Telescope (EHT) Collaboration has successfully produced images of two supermassive black holes, enabling novel tests of black holes and their accretion flows on horizon scales. The EHT has so far published total intensity and linear polarization images, while upcoming images may include circular polarization, rotation measure, and spectral index, each of which reveals different aspects of the plasma and space-time. The next-generation EHT (ngEHT) will greatly enhance these studies through wider recorded bandwidths and additional stations, leading to greater signal-to-noise, orders of magnitude improvement in dynamic range, multi-frequency observations, and horizon-scale movies. In this paper, we review how each of these different observables informs us about the underlying properties of the plasma and the spacetime, and we discuss why polarimetric studies are well-suited to measurements with sparse, long-baseline coverage.


Comment: Submitted for Galaxies Special Issue "From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science"

Subject: Astrophysics - High Energy Astrophysical Phenomena


A single GRMHD snapshot ray-traced and scaled to Sgr~A$^*$ properties, with three decades in dynamic range shown.  So far, total intensity maps have been produced for both Sgr~A$^*$ and M87$^*$, a linear polarization map has been produced for M87$^*$, and the remaining observables have yet to be generated for either source.  In the era of ngEHT, we will have access to each of these observables with improved dynamic range and time-domain information, which will greatly inform models of the black hole accretion flow.