[DSRP Evidence](https://dsrpevidence.org/)

# 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

## Details

**Authors** Rebecca A. Lewis-Merrill et al.

**Year** 2026

**Publisher** The Astrophysical Journal

**Kind of work** article

**Discipline** Astronomy

[Read it at the publisher](https://doi.org/10.3847/1538-4357/ae878c) 
10.3847/1538-4357/ae878c

## In authors' words

### 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 at the center of our Galaxy, in the Gaia Celestial Reference Frame 3 (Gaia-CRF3). This reference frame realizes the International Celestial Reference System, 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 observations into Gaia-CRF3. We find the proper motion of Sgr A*-IR in Gaia-CRF3 to be μα*=−3.093±0.085 mas/yr and μδ=−5.62±0.13 mas/yr. 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 excludes any intermediate-mass black hole companion with mass ≳4×10^4 M⊙ within a distance of ∼0.01 pc.

### What they set out to do (purpose)

Precisely measure the motion of the Milky Way's central supermassive black hole in an absolute, quasar-defined coordinate frame and use it to test for a hidden companion black hole.

### Who or what was studied (sample)

The infrared counterpart to Sagittarius A* at the Galactic Center, observed via Keck adaptive optics.

### How they did it (methods)

Combined Keck adaptive-optics astrometry with Gaia and Hubble Space Telescope data, using a custom reference-star selection method to transform observations into Gaia-CRF3.

### What they found (results)

The infrared counterpart to Sagittarius A* has a measured proper motion of −3.093 mas/yr (RA) and −5.62 mas/yr (Dec) in the Gaia-CRF3 absolute reference frame, with acceleration limits ruling out an intermediate-mass black hole companion more massive than ~4×10^4 solar masses within 0.01 parsecs.

## Commentary

### In short

The finding shows that an object's measured motion is inseparable from the reference frame chosen to describe it: the same black hole's motion is only meaningful once expressed within a specific adopted coordinate perspective.

**Patterns it shows** P

Shows the structure is there

**Added** 2026-09-16

**How to cite this** Rebecca A. Lewis-Merrill et al. (2026). 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. The Astrophysical Journal.