A research team has analyzed seven years of ALMA (Atacama Large Millimeter/submillimeter Array) observations and discovered a remarkably clear 52-minute periodic signal from Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way. The team consisted of Kazuki Yanagisawa from the Graduate School of Science and Technology, Professor Tomoharu Oka from the Faculty of Science and Technology, as well as other researchers from Keio University, the National Astronomical Observatory of Japan and National Institute of Technology at Tokyo College. The signal, observed on July 22, 2021, is attributed to relativistic Doppler beaming produced by a compact hotspot orbiting extremely close to the black hole at about one-third the speed of light.
The analysis constrains the inclination of the system to ~172°, meaning that Earth is observing the accretion disk from almost directly "below." This discovery provides new observational constraints on the relativistic dynamics and geometry of matter in the immediate environment of a supermassive black hole.
These findings were published in The Astrophysical Journal on December 1, 2025.
