Letter to the Editor

High-mass microquasars from binary to black hole scale

Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon, Université de Lyon, Université Lyon 1, CNRS, UMR 5574, 46 allée d’Italie, 69364 Lyon Cedex 07, France

^⋆ Corresponding author: Rolf.Walder@ens-lyon.fr

Received: 14 July 2025
Accepted: 7 August 2025

Abstract

We present a 3D hydrodynamical simulation of a wind-accreting high-mass microquasar, from 30 binary separations (d) to 256 black hole (BH) gravitational radii, over one-sixth of a full orbit in time, with system parameters inspired by Cyg X-1. The simulation allows key system components to emerge naturally as inter-dependent quasi-stationary parts of an inherently multi-scale flow. The BH accretion disk is highly eccentric, with spirally shaped accreting and decreting zones. Its flow field is consistent with elliptical orbits confocal at the BH. The disk structure relates to its feeding: a cold 3D accretion cone channels matter from opposite the L1 point and within 2/3d from the BH toward the disk. Above and below the disk, a polytropic atmosphere establishes, with temperatures one-tenth of the virial temperature. A hot cocoon of shocked wind material engulfs the BH accretion structure on scales of d/10. We hypothesize that the shocks may accelerate particles and the atmosphere may up-scatter photons to GeV energies and beyond. An Archimedian spiral is apparent out to at least 10d, as the orbiting BH perturbs the homogeneous donor star wind. Our simulation offers a coherent cross-scale perspective that allows us to contextualize observations, interpretations, and specific models.