Instability of Circumnuclear Gas Supply as An Origin of "Changing-look" Phenomenon of Supermassive Blackholes

TL;DR

This paper investigates the 'Changing-look' phenomenon in supermassive black holes, proposing that it results from unstable circumnuclear gas supply causing accretion rate variations, distinct from traditional disk instability models.

Contribution

It identifies a characteristic timescale for the CL phenomenon and links it to SMBH mass, proposing a new explanation involving gas supply fluctuations.

Findings

Larger SMBHs have shorter CL timescales.

SMBH mass correlates with CL timescale, contrasting with traditional variability models.

CL phenomenon likely caused by sudden changes in circumnuclear gas supply.

Abstract

The origin of the "Changing-look" (CL) phenomenon in supermassive black holes (SMBHs) remains an open issue. This study aims to shed light on this phenomenon by focusing on a sample that encompasses all known repeating CL active galactic nuclei (AGNs). Through the identification of a characteristic time scale for the CL phenomenon, it was observed that larger SMBHs possess shorter characteristic timescales, while smaller SMBHs exhibit longer timescales. These findings reveal a significant contrast to the traditional AGN variability that has been adequately explained by the AGN's disk instability model. This stark discrepancy highlights a distinct origin of the CL phenomenon, distinguishing it from traditional AGN variability. By properly predicting the characteristic time scale and its dependence on SMBH mass, we propose that the CL phenomenon is likely a result of a variation in accretion rate caused by a sudden change in the supply of circumnuclear gas during the transition between active and passive SMBH fueling stages.