On the possible orbital motion of Sgr A* in the smooth potential of the Milky Way

TL;DR

This study investigates the potential orbital oscillations of the supermassive black hole Sgr A* within the Milky Way, considering various Galactic potential models and recent velocity measurements, finding that oscillations are limited to a few parsecs mainly by the nuclear stellar disk.

Contribution

It provides the first detailed analysis of Sgr A*'s possible orbital motion considering modern Galactic potential models and velocity constraints, highlighting the dominant role of the nuclear stellar disk.

Findings

Oscillation amplitude depends on Galactic potential components.

Presence of a nuclear stellar disk limits SMBH oscillations to about 13 pc.

Oscillations are minimal when considering the nuclear stellar disk.

Abstract

The modern accuracy of measurements allows the residual/peculiar (Galactocentric) velocity of the supermassive black hole (SMBH) in our Galaxy, Sgr A*, on the order of several kilometers per second. We integrate possible orbits of the SMBH along with the surrounding nuclear star cluster (NSC) for a barred model of the Galaxy using modern constraints on the components of the SMBH Galactocentric velocity. Is is shown that the range of oscillations of the SMBH + NSC in a regular Galactic field in the plane of the Galaxy allowed by these constraints strongly depends on the set of central components of the Galactic potential. If the central components are represented only by a bulge/bar, for a point estimate of the SMBH Galactocentric velocity, the oscillation amplitude does not exceed 7 pc in the case that a classical bulge is present and reaches 25 pc if there is no bulge; with SMBH velocity components within the $2\sigma$ significance level, the amplitude can reach 15 and 50 pc, respectively. However, when taking into account the nuclear stellar disk (NSD), even in the absence of a bulge, the oscillation amplitude is only 5 pc for the point estimate of the SMBH velocity, and 10 pc for the $2\sigma$ significance level. Thus, the possible oscillations of the SMBH + NSC complex from the confirmed components of the Galaxy's potential are mostly limited by the NSD, and even taking into account the uncertainty of the mass of the latter, the oscillation amplitude can hardly exceed $13\,\text{pc}=6'$.