Abstract We analyzed 11 epochs of archival Atacama Large Millimeter/submillimeter Array (ALMA) data to investigate the flux density variability of Sgr A* at 340 GHz. In one epoch, the light curve exhibits two short-timescale components with characteristic periods of ∼30 and ∼50 minutes. While the corresponding peaks in the periodogram are highly significant under a white-noise assumption, their significance decreases below 3 σ when red-noise variability is taken into account, and we therefore do not regard them as statistically significant periodic detections. Nevertheless, the observed timescales are comparable to the orbital period near the innermost stable circular orbit of Sgr A*, and the light curve shows phase-dependent structure and amplitude evolution consistent with orbital modulation. We find that the variability is well described by a model involving multiple orbiting hotspots with decaying emission. This interpretation suggests that both periodic and nonperiodic variability in Sgr A* may arise from a common physical origin in orbiting structures within the accretion flow, providing a unified framework for its millimeter variability.
Yanagisawa et al. (2026) studied this question.