Supermassive black-hole imaging with a self-consistent electron-temperature prescription

The recent 230 GHz observations by the Event Horizon Telescope have resolved the innermost structure of the M87 galaxy, revealing a ring-like feature consistent with thermal synchrotron emission from a magnetized torus surrounding a rotating supermassive black hole. Moreover, Global Millimeter VLBI Array observations at 86 GHz have revealed a larger-scale, edge-brightened jet with clear signatures of non-thermal emission. The theoretical modelling of these observations involves advanced general-relativistic magnetohydrodynamic simulations of magnetized accretion disks around rotating black holes, together with the associated synchrotron emission, which is normally treated with simplified expressions for the electron temperature and assuming a purely thermal distribution. However, an important non-thermal component is expected to be present, making the thermal-emission model not only an approximation, but also a source of degeneracy in the modelling. In view of this, we here present the first application of an ab-initio approach to the electron temperature derived from microscopic simulations of turbulent collisionless plasmas. The novel method, which has no tuneable coefficients and is fully specified by the thermodynamical and magnetic properties of the plasma, provides a better description of the jet morphology and width at 86 GHz, as well as of the broadband spectral emission. These findings highlight the importance of incorporating microscopic plasma physics in black-hole imaging and emphasise the crucial role of magnetic reconnection in electron heating and acceleration processes.

💡 Research Summary

This paper presents a novel, first‑principles approach to modeling the electron temperature and energy distribution in the vicinity of the supermassive black hole M87*, aiming to reconcile the 230 GHz Event Horizon Telescope (EHT) ring image with the 86 GHz Global Millimeter VLBI Array (GMVA) edge‑brightened jet. The authors combine state‑of‑the‑art general‑relativistic magnetohydrodynamic (GRMHD) simulations performed with the BHAC code and general‑relativistic radiative transfer (GRRT) calculations using BHOSS. The GRMHD setup employs a Kerr black hole with spin a⋆≈0.94, a Fishbone‑Moncrief torus (inner radius 20 M, pressure maximum at 40 M) threaded by a weak poloidal magnetic field (β=100) that evolves into a magnetically arrested disk (MAD) state. The computational domain spans r∈