# The Analogous Structure of Accretion Flows in Supermassive and Stellar Mass Black Holes: New Insights from Faded Changing-Look Quasars

## TL;DR

This study demonstrates that the structure of accretion flows in supermassive black holes and stellar-mass black holes are analogous, with observed spectral correlations supporting a unified model across different mass scales and accretion states.

## Contribution

It provides new observational evidence from faded changing-look quasars that supports the scaling of accretion flow geometry from X-ray binaries to AGN across different states.

## Key findings

- Observed alpha_OX and Eddington ratio correlation in AGN mirrors X-ray binary state transitions.
- Inversion of alpha_OX-Eddington ratio correlation occurs at ~10^-2 Eddington ratio.
- Accretion flow structures scale across black hole masses and states.

## Abstract

Despite their factor of ~10^8 difference in black hole mass, several lines of evidence suggest possible similarities between black hole accretion flows in active galactic nuclei (AGN) and Galactic X-ray binaries. However, it is still unclear whether the geometry of the disk-corona system in X-ray binaries directly scale up to AGN, and whether this analogy still holds in different accretion states. We test this AGN/X-ray binary analogy, by comparing the observed correlations between the UV-to-X-ray spectral index (alpha_OX) and Eddington ratio in AGN to those predicted from observations of X-ray binary outbursts. This approach probes the geometry of their disk-corona systems as they transition between different accretion states. We use new Chandra X-ray and ground-based rest-UV observations of faded 'changing-look' quasars to extend this comparison to lower Eddington ratios of <10^-2, where observations of X-ray binaries predict a softening of alpha_OX in AGN. We find that the observed correlations between alpha_OX and Eddington ratio of AGN displays a remarkable similarity to accretion state transitions in prototypical X-ray binary outbursts, including an inversion of this correlation at a critical Eddington ratio of ~10^-2. Our results suggest that the structures of black hole accretion flows directly scale across a factor of ~10^8 in black hole mass and across different accretion states, enabling us to apply theoretical models of X-ray binaries to explain AGN phenomenology.