The Galactic Center Reference Frame: A 30-Year Solution

Abstract

Stellar orbits probe the metric of and mass around the Sgr A* massive black hole. To enable study of the black hole, the surrounding mass, and tests of gravity, a precise reference frame must be established and maintained. We present an updated stellar maser-based reference frame for the inner parsec of the Galactic Center, referenced to the radio continuum of Sgr A*. This work synthesizes 30 years of astrometric observations of 15 SiO stellar masers and the Sgr A* continuum at 43 GHz. The uncertainty in the mean offset of the maser ensemble from Sgr A* is 0.08 mas in the current epoch and will decay to 0.10 mas by 2030. At a distance of 8.2 kpc, these correspond to position uncertainties of 0.6 AU and 0.8 AU, respectively, which is similar to or smaller than the stellar SiO-emitting region. The mean maser proper motion uncertainties are 0.05 mas yr⁻¹ in RA and 0.08 mas yr⁻¹ in Dec, corresponding to 1.8 km s⁻¹ and 3.2 km s⁻¹. The reference frame stability between IR and maser astrometry is 10~μas yr⁻¹ (0.40 km s⁻¹) in RA and 15 μas yr⁻¹ (0.57 km s⁻¹) in Dec. The masers show substantial variability in flux density and velocity structure, most notably IRS~7, which shows a 30-fold brightening in a blueshifted component since 2022. This variability may set a floor on future astrometry improvements and especially measurements of radial acceleration.

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BibTeX RIS

BibTeX

@misc{darling2026galactic,
  title = {{The Galactic Center Reference Frame: A 30-Year Solution}},
  author = {Jeremy Darling and Jennie Paine and Matthew Hosek Jr. and Shoko Sakai and Stefan Gillessen and Tatsuya Akiba-Lewis and Andrea Ghez and Frank Eisenhauer and Reinhard Genzel},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.31766},
  eprint = {2610.31766},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.31766},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - The Galactic Center Reference Frame: A 30-Year Solution
AU  - Jeremy Darling
AU  - Jennie Paine
AU  - Matthew Hosek Jr.
AU  - Shoko Sakai
AU  - Stefan Gillessen
AU  - Tatsuya Akiba-Lewis
AU  - Andrea Ghez
AU  - Frank Eisenhauer
AU  - Reinhard Genzel
PY  - 2026
DA  - 2026/10/22
PB  - arXiv
DO  - 10.48550/arxiv.2610.31766
UR  - https://arxiv.org/abs/2610.31766
AB  - Stellar orbits probe the metric of and mass around the Sgr A* massive black hole. To enable study of the black hole, the surrounding mass, and tests of gravity, a precise reference frame must be established and maintained. We present an updated stellar maser-based reference frame for the inner parsec of the Galactic Center, referenced to the radio continuum of Sgr A*. This work synthesizes 30 years of astrometric observations of 15 SiO stellar masers and the Sgr A* continuum at 43 GHz. The uncertainty in the mean offset of the maser ensemble from Sgr A* is 0.08 mas in the current epoch and will decay to 0.10 mas by 2030. At a distance of 8.2 kpc, these correspond to position uncertainties of 0.6 AU and 0.8 AU, respectively, which is similar to or smaller than the stellar SiO-emitting region. The mean maser proper motion uncertainties are 0.05 mas yr^−1 in RA and 0.08 mas yr^−1 in Dec, corresponding to 1.8 km s^−1 and 3.2 km s^−1. The reference frame stability between IR and maser astrometry is 10~μas yr^−1 (0.40 km s^−1) in RA and 15 μas yr^−1 (0.57 km s^−1) in Dec. The masers show substantial variability in flux density and velocity structure, most notably IRS~7, which shows a 30-fold brightening in a blueshifted component since 2022. This variability may set a floor on future astrometry improvements and especially measurements of radial acceleration.
ER  -

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