Indication of Another Intermediate-mass Black Hole in the Galactic Center

Shunya Takekawa,Yuhei Iwata,Tomoharu Oka,Shiho Tsujimoto,Mariko Nomura

doi:10.3847/2041-8213/aafb07

Abstract

Abstract We report the discovery of molecular gas streams orbiting around an invisible massive object in the central region of our Galaxy, based on the high-resolution molecular line observations with the Atacama Large Millimeter/submillimeter Array. The morphology and kinematics of these streams can be reproduced well through two Keplerian orbits around a single point mass of (3.2 ± 0.6) × 104 M ⊙. We also found ionized gas toward the inner part of the orbiting gas, indicating dissociative shock and/or photoionization. Our results provide new circumstantial evidences for a wandering intermediate-mass black hole in the Galactic center, suggesting also that high-velocity compact clouds can be probes of quiescent black holes that abound in our Galaxy.

Highlights

Intermediate-mass black holes (IMBHs) with masses of 102–105 M are the missing link between stellar-mass and supermassive black holes (e.g., Ebisuzaki et al 2001)
We report the discovery of molecular gas streams orbiting around an invisible massive object in the central region of our Galaxy, based on the high-resolution molecular line observations with the Atacama Large Millimeter/submillimeter Array (ALMA)
Our results provide new circumstantial evidences for a wandering intermediate-mass black hole in the Galactic center, suggesting that high-velocity compact clouds can be probes of quiescent black holes abound in our Galaxy

Summary

INTRODUCTION

Intermediate-mass black holes (IMBHs) with masses of 102–105 M are the missing link between stellar-mass and supermassive black holes (e.g., Ebisuzaki et al 2001). Massive IMBHs may lurk in the nuclei of dwarf galaxies and/or globular clusters (e.g., Reines et al 2013; Baldassare et al 2015; Kızıltan et al 2017). These results have been argued upon, and none of the IMBH candidates are accepted as definitive (e.g., Ebisawa et al 2003; Strader et al 2012). HCN–0.009–0.044 is more compact (∼ 1 pc) than any previously known HVCCs (2–5 pc), and its velocity width (∼ 40 km s−1) is typical to those of HVCCs. The compactness, kinematics, and absence of luminous stellar counterpart can be explained by the high-velocity plunge of an invisible compact object into a molecular cloud (Takekawa et al 2017; Nomura et al 2018).

OBSERVATIONS

Spatial/Velocity Structure and Physical Condition

Keplerian Model

Indication of an IMBH