The Swansong of the Galactic Center Source X7: An Extreme Example of Tidal Evolution near the Supermassive Black Hole

TL;DR

Over two decades of high-resolution near-infrared observations reveal that the elongated dust and gas feature X7 near the Galactic Center's supermassive black hole is undergoing extreme tidal evolution, with orbital and morphological changes consistent with black hole influence.

Contribution

This study provides the first detailed orbital and morphological analysis of X7, demonstrating its evolution due to tidal forces and proposing a new origin scenario involving binary system collision ejecta.

Findings

X7 has a mildly eccentric orbit with a 170-year period heading towards periapse in 2036.

X7's morphology has become more elongated, with a stable position angle.

X7's brightness and temperature suggest a constant mass of about 50 Earth masses.

Abstract

We present two decades of new high-angular-resolution near-infrared data from the W. M. Keck Observatory that reveal extreme evolution in X7, an elongated dust and gas feature, presently located half an arcsecond from the Galactic Center supermassive black hole. With both spectro-imaging observations of Br-{\gamma} line-emission and Lp (3.8 {\mu}m) imaging data, we provide the first estimate of its orbital parameters and quantitative characterization of the evolution of its morphology and mass. We find that the leading edge of X7 appears to be on a mildly eccentric (e~0.3), relatively short-period (170 years) orbit and is headed towards periapse passage, estimated to occur in ~2036. Furthermore, our kinematic measurements rule out the earlier suggestion that X7 is associated with the stellar source S0-73 or with any other point source that has overlapped with X7 during our monitoring period. Over the course of our observations, X7 has (1) become more elongated, with a current length-to-width ratio of 9, (2) maintained a very consistent long-axis orientation (position angle of 50 deg), (3) inverted its radial velocity differential from tip to tail from -50 to +80 km/sec, and (4) sustained its total brightness (12.8 Lp magnitudes at the leading edge) and color temperature (425 K), which suggest a constant mass of ~50 MEarth. We present a simple model showing that these results are compatible with the expected effect of tidal forces exerted on it by the central black hole and we propose that X7 is the gas and dust recently ejected from a grazing collision in a binary system.