Discovery of a Dense Association of Stars in the Vicinity of the Supermassive Black Hole Sgr A*

Abstract

We focus on a sample of 42 sources in the vicinity of the bow-shock source IRS 1W (N-sources), located at the distance of $6.05''$ north-east of the supermassive black hole (SMBH) Sagittarius A* (Sgr A*), within the radius of $1.35''$. We present the first proper motion measurements of N-sources and find that a larger subset of N-sources (28 sources) exhibit a north-westward flying angle. These sources can be bound by an intermediate mass black hole (IMBH) or the concentration that we observe is due to a disk-like distribution projection along the line of sight. We detect the N-sources in $H$, $K_s$, and $L$' bands. The north-westward flying sources could be a bound collection of stars. We discuss a tentative existence of an IMBH or an inclined disk distribution to explain a significant overdensity of stars. The first scenario of having an IMBH implies the lower limit of $\sim 10^4~M_\odot$ for the putative IMBH. Our measurements for the first time reveal that the dense association of stars containing IRS 1W is a co-moving group of massive, young stars. This stellar association might be the remnant core of a massive stellar cluster that is currently being tidally stripped as it inspirals towards Sgr A*. The second scenario suggests that the appearance of the N-sources might be influenced by the projection of a disk-like distribution of younger He-stars and/or dust-enshrouded stars.