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-source region), located at a distance of 6.″05 northeast of the supermassive black hole 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–west (NW) 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 the H, K s , and L′ bands. The NW-ward flying sources could be a bound collection of stars. We discuss the tentative existence of an IMBH or an inclined disk distribution to explain the significant overdensity of stars. The first scenario of having an IMBH implies the lower limit of ∼104 M ⊙ for the putative IMBH. Our measurements for the first time reveal that the dense association of stars containing IRS 1W is a comoving 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 toward 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.