The Accretion flow in M87 is really MAD

TL;DR

This paper demonstrates that the accretion flow in M87 is best described by the MAD model, as it aligns with observed rotation measures, unlike the SANE model which overestimates them significantly.

Contribution

The study combines observational data with GRMHD simulations to conclusively identify the accretion mode in M87 as MAD, resolving previous uncertainties.

Findings

MAD model matches observed rotation measures in M87

SANE model overestimates rotation measures by over two orders of magnitude

Supports MAD as the dominant accretion mode in M87

Abstract

The supermassive black holes in most galaxies in the universe are powered by hot accretion flows. Both theoretical analysis and numerical simulations have indicated that, depending on the degree of magnetization, black hole hot accretion flow is divided into two modes, namely SANE (standard and normal evolution) and MAD (magnetically arrested disk). It has been an important question which mode the hot accretion flows in individual sources should belong to in reality, SANE or MAD. This issue has been investigated in some previous works but they all suffer from various uncertainties. By using the measured rotation measure values in the prototype low-luminosity active galactic nuclei in {M87} at 2, 5, and 8 GHz along the jet at various distances from the black hole, combined with three dimensional general relativity magnetohydrodynamical numerical simulations of SANE and MAD, we show in this paper that the predicted rotation measure values by MAD are well consistent with observations, while the SANE model overestimates the rotation measure by over two orders of magnitude thus is ruled out.