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arXiv · 2511.02186

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

Kazuki Yanagisawa·Tomoharu Oka·Ryo Ariyama·Kazuki Yanagihara·Yuhei iwata·Mikiya M. Takahashi
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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 5{\sigma}. Modeling with a Doppler-boosted hotspot scenario yields an orbital radius of ~4 Schwarzschild radii and a disk inclination of 8$^\circ$ (or 172$^\circ$), 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.

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Kazuki Yanagisawa, Tomoharu Oka, Ryo Ariyama, Kazuki Yanagihara, Yuhei iwata, Mikiya M. Takahashi. 2025-11-04. A Face-on Accretion Disk Geometry Revealed by Millimeter-wave Periodicity in Sgr A$^*$. https://arxiv.org/abs/2511.02186

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