Absolute Motion of the Infrared Counterpart to Sagittarius A* in the Gaia Celestial Reference Frame 3 and…

Abstract

We report the first proper motion and acceleration measurements of the infrared (IR) counterpart to Sagittarius A* (Sgr A*-IR), the supermassive black hole (SMBH) at the center of our Galaxy, in the Gaia-Celestial Reference Frame (Gaia-CRF3). This reference frame realizes the International Celestial Reference System (ICRS), which is an absolute reference coordinate system defined by quasars. A combination of Gaia and Hubble Space Telescope data was used to transform Keck adaptive optics (AO) observations into Gaia-CRF3. We developed a method for selecting reference stars that minimizes astrometric transformation errors (statistical error = $0.10-0.63$ mas) and drift of the coordinate system (systematic error ∼ 0.01 mas/yr). We find the proper motion of Sgr A*-IR in Gaia-CRF3 to be μ_α^* = −3.093 ± 0.085 mas yr⁻¹ and μ_δ= −5.62 ± 0.13 mas yr⁻¹ with the initial position at t₀ = 2016.0 of R.A. = 266.41680848 ± 0.00000029 deg and DEC = -29.00783947 ± 0.00000050 deg, which translates to a precision of 1.05 mas in R.A. and 1.79 mas DEC. This is consistent with the astrometric measurements of the radio counterpart to Sgr A* by \citet{Xu_2022}. We also place a 2σ upper constraint of the acceleration of Sgr A*-IR on the sky at 0.061 mas yr⁻². This acceleration limit on Sgr A*-IR excludes any intermediate-mass black hole companion with mass ≳ 4× 10⁴ M_⊙ within a distance of ∼0.01 pc, consistent with previous studies. With the release of Gaia Data Release 4, we predict these limits will be improved by at least a factor of two.

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BibTeX

@misc{lewismerrill2026absolute,
  title = {{Absolute Motion of the Infrared Counterpart to Sagittarius A* in the Gaia Celestial Reference Frame 3 and Limits on an Intermediate-mass Black Hole Companion}},
  author = {Rebecca A. Lewis-Merrill and Tuan Do and Matthew W. Hosek Jr. and Gregory David Martinez and Shoko Sakai and Kelly Kosmo O'Neil and Grant Weldon and Abhimat Gautam and Zoë Haggard and Andrea M. Ghez and Jessica R. Lu and Keith Matthews},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.04077},
  eprint = {2609.04077},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.04077},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Absolute Motion of the Infrared Counterpart to Sagittarius A* in the Gaia Celestial Reference Frame 3 and Limits on an Intermediate-mass Black Hole Companion
AU  - Rebecca A. Lewis-Merrill
AU  - Tuan Do
AU  - Matthew W. Hosek Jr.
AU  - Gregory David Martinez
AU  - Shoko Sakai
AU  - Kelly Kosmo O'Neil
AU  - Grant Weldon
AU  - Abhimat Gautam
AU  - Zoë Haggard
AU  - Andrea M. Ghez
AU  - Jessica R. Lu
AU  - Keith Matthews
PY  - 2026
DA  - 2026/09/03
PB  - arXiv
DO  - 10.48550/arxiv.2609.04077
UR  - https://arxiv.org/abs/2609.04077
AB  - We report the first proper motion and acceleration measurements of the infrared (IR) counterpart to Sagittarius A* (Sgr A*-IR), the supermassive black hole (SMBH) at the center of our Galaxy, in the Gaia-Celestial Reference Frame (Gaia-CRF3). This reference frame realizes the International Celestial Reference System (ICRS), which is an absolute reference coordinate system defined by quasars. A combination of Gaia and Hubble Space Telescope data was used to transform Keck adaptive optics (AO) observations into Gaia-CRF3. We developed a method for selecting reference stars that minimizes astrometric transformation errors (statistical error = $0.10-0.63$ mas) and drift of the coordinate system (systematic error ∼ 0.01 mas/yr). We find the proper motion of Sgr A*-IR in Gaia-CRF3 to be μ_α^* = −3.093 ± 0.085 mas yr^−1 and μ_δ= −5.62 ± 0.13 mas yr^−1 with the initial position at t_0 = 2016.0 of R.A. = 266.41680848 ± 0.00000029 deg and DEC = -29.00783947 ± 0.00000050 deg, which translates to a precision of 1.05 mas in R.A. and 1.79 mas DEC. This is consistent with the astrometric measurements of the radio counterpart to Sgr A* by \citet{Xu_2022}. We also place a 2σ upper constraint of the acceleration of Sgr A*-IR on the sky at 0.061 mas yr^−2. This acceleration limit on Sgr A*-IR excludes any intermediate-mass black hole companion with mass ≳ 4× 10^4 M_⊙ within a distance of ∼0.01 pc, consistent with previous studies. With the release of Gaia Data Release 4, we predict these limits will be improved by at least a factor of two.
ER  -

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