The Second Galactic Center Black Hole?; A Possible Detection of Ionized Gas Orbiting around an IMBH embedded in the Galactic Center IRS13E complex

TL;DR

This study reports the detection of ionized gas with high velocity and compact size near the Galactic Center, suggesting the presence of an intermediate mass black hole in the IRS13E complex, which could be a second black hole in the region.

Contribution

First detection of ionized gas with properties indicating it may orbit an IMBH in IRS13E, providing evidence for a potential second black hole in the Galactic Center.

Findings

Ionized gas with large velocity width (~650 km/s) detected in IRS13E

Estimated enclosed mass of ~10^4 Msun consistent with an IMBH

Possible X-ray counterpart supports the black hole hypothesis

Abstract

The Galactic Center is the nuclear region of the nearest spiral galaxy, Milky Way, and contains the supermassive black hole with M~4x10^6 Msun, Sagittarius A* (Sgr A*). One of basic questions about the Galactic Center is whether Sgr A* alone exists as a "massive" black hole in the region or not. The IRS13E complex is a very intriguing IR object which contains a large dark mass comparable to the mass of an intermediate mass black hole (IMBH) from the proper motions of the main member stars. However, the existence of the IMBH remains controversial. There are some objections to accepting the existence of the IMBH. In this study, we detected ionized gas with a very large velocity width (Delta v_{FWZI} ~ 650 km/s) and a very compact size (~400 AU) in the complex using ALMA. We also found an extended component connecting with the compact ionized gas. The properties suggest that this would be an ionized gas flow on the Keplerian orbit with high eccentricity. The enclosed mass is estimated to be 10^4 Msun by the analysis of the orbit. The mass does not conflict with the upper limit mass of the IMBH around Sgr A* which is derived by the long-term astrometry with VLBA. In addition, the object probably has an X-ray counterpart. Consequently, a very fascinated possibility is that the detected ionized gas is rotating around an IMBH embedded in the IRS13E complex.