# A geometric distance measurement to the Galactic Center black hole with 0.3% uncertainty

## TL;DR

This paper precisely measures the distance to the Galactic Center using 27 years of observations of star S2, achieving a 0.3% uncertainty through astrometry, spectroscopy, and interferometry, confirming gravitational redshift effects.

## Contribution

It provides the most accurate geometric measurement of R0 to date, combining long-term data with interferometry to improve precision and confirm gravitational redshift detection.

## Key findings

- Distance to Galactic Center: 8178 ± 13 (stat) ± 22 (sys) pc
- Redshift detection at 20 sigma significance
- Measurement precision of 0.3% for R0

## Abstract

We present a 0.16% precise and 0.27% accurate determination of R0, the distance to the Galactic Center. Our measurement uses the star S2 on its 16-year orbit around the massive black hole Sgr A* that we followed astrometrically and spectroscopically for 27 years. Since 2017, we added near-infrared interferometry with the VLTI beam combiner GRAVITY, yielding a direct measurement of the separation vector between S2 and Sgr A* with an accuracy as good as 20 micro-arcsec in the best cases. S2 passed the pericenter of its highly eccentric orbit in May 2018, and we followed the passage with dense sampling throughout the year. Together with our spectroscopy, in the best cases with an error of 7 km/s, this yields a geometric distance estimate: R0 = 8178 +- 13(stat.) +- 22(sys.) pc. This work updates our previous publication in which we reported the first detection of the gravitational redshift in the S2 data. The redshift term is now detected with a significance level of 20 sigma with f_redshift = 1.04 +- 0.05.