Detection of faint stars near SgrA* with GRAVITY

TL;DR

Using the GRAVITY instrument's high-resolution interferometry, the study detected faint stars near SgrA*, enabling future measurements of the black hole's spin through stellar orbit analysis.

Contribution

This work demonstrates the capability of GRAVITY to detect faint stars close to SgrA*, advancing the potential for measuring the black hole's spin via stellar orbits.

Findings

Detected a faint star of magnitude 18.9 near SgrA*

Observed a brighter star of magnitude 16.6 at 130 mas from SgrA*

Showed that future upgrades could detect stars fainter than magnitude 19

Abstract

The spin of the supermassive black hole that resides at the Galactic Centre can in principle be measured by accurate measurements of the orbits of stars that are much closer to SgrA* than S2, the orbit of which recently provided the measurement of the gravitational redshift and the Schwarzschild precession. The GRAVITY near-infrared interferometric instrument combining the four 8m telescopes of the VLT provides a spatial resolution of 2-4 mas, breaking the confusion barrier for adaptive-optics-assisted imaging with a single 8-10m telescope. We used GRAVITY to observe SgrA* over a period of six months in 2019 and employed interferometric reconstruction methods developed in radio astronomy to search for faint objects near SgrA*. This revealed a slowly moving star of magnitude 18.9 in K band within 30mas of SgrA*. The position and proper motion of the star are consistent with the previously known star S62, which is at a substantially larger physical distance, but in projection passes close to SgrA*. Observations in August and September 2019 easily detected S29, with K-magnitude of 16.6, at approximately 130 mas from SgrA*. The planned upgrades of GRAVITY, and further improvements in the calibration, hold the promise of finding stars fainter than magnitude 19 at K.