A Face-on Accretion Disk Geometry Revealed by Millimeter-wave Periodicity in Sgr A^*

2025/11/04 by Yanagisawa, Kazuki, Oka, Tomoharu, Ariyama, Ryo +3
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)

paper · doi:10.48550/arxiv.2511.02186

Abstract

We analyzed 77 epochs of Atacama Large Millimeter/submillimeter Array (ALMA) archival data to investigate flux variability in Sagittarius A^* (Sgr A^*), the supermassive black hole at the Galactic Center. Among these, we identified a rare but unusually clear and coherent ~52-minute sinusoidal modulation at 230 GHz, with a statistical significance exceeding 5σ. Modeling with a Doppler-boosted hotspot scenario yields an orbital radius of ~4 Schwarzschild radii and a disk inclination of 8^∘ (or 172^∘), providing the first direct millimeter wavelength constraint on the inner accretion flow geometry. This nearly face-on inclination is in good agreement with previous constraints from GRAVITY and EHT observations. These findings provide robust, independent evidence that millimeter-wave periodicity can directly probe the innermost accretion flow geometry, offering a powerful complement to variability studies at infrared and X-ray wavelengths.

Citations

• First mid-infrared detection and modeling of a flare from Sgr A*
• Multiwavelength Observations of Sgr A*. II. 2019 July 21 and 26
• Near-Infrared Flux Distribution of Sgr A* from 2005-2022: Evidence for an Enhanced Accretion Episode in 2019
• Polarimetry and astrometry of NIR flares as event horizon scale, dynamical probes for the mass of Sgr A*
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• Oscillation Phenomena in the disk around the massive black hole Sagittarius A*

Related

• Radio Variability of Sgr A* at Centimeter Wavelengths
• Flares of Sagittarius a* at Millimeter Wavelengths
• Advection-Dominated Accretion Model for Sagittarius A^*: Evidence for a 10⁶\msun Black Hole at the Galactic Center
• The Structure and Variability of Sagittarius A*: Zooming in to the Supermassive Black Hole at the Galactic Center
• Observing a Black Hole Event Horizon: (Sub)Millimeter VLBI of Sgr A*