Astronomers have confirmed the existence of a persistent outflow of gas originating from Sagittarius A*, the supermassive black hole located at the heart of the Milky Way. This discovery, detailed in a study published in The Astrophysical Journal Letters on June 5, 2026, by Northwestern University researchers Mark Gorski and Lena Murchikova, resolves a decades-old mystery regarding the apparent inactivity of the galaxy’s central engine.
The research team utilized the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile to conduct a high-resolution survey of cold molecular gas within the central parsec of the galaxy. By aggregating over 100 hours of observational data collected between 2017 and 2021, the team mapped the 12CO(J=2−1) rotational transition of carbon monoxide at 230 GHz. This specific transition is a standard tracer for cold molecular material, allowing astronomers to probe the dense, low-temperature regions of the interstellar medium that are otherwise invisible to optical telescopes.
This observational process required sophisticated signal processing to mitigate the intense, fluctuating radio emission from Sgr A* itself, which typically obscures fainter surrounding structures. The black hole acts as a bright, variable point source, with millimeter-wave flux that can shift by 20 percent or more within a single observation session. Without removing this variability, the black hole’s own glow would wash out the vastly fainter CO emission from surrounding gas structures, which emit at brightness temperatures around 30 millikelvin.
To isolate the faint molecular signals, Gorski and Murchikova employed the UVMultiFit software package to model and subtract the black hole’s variable radio output at 15-to-30-second intervals. This technical refinement allowed for the reconstruction of a molecular gas map with 100 times the sensitivity and 80 times the sharpness of previous attempts. The resulting imagery revealed a distinct, cone-shaped cavity extending approximately one parsec, oriented south-southwest toward the black hole.
Cross-referencing this molecular void with archival data from NASA’s Chandra X-ray Observatory provided critical validation for the team’s findings. The cone-shaped region, which appeared empty in the ALMA carbon monoxide map, was found to be filled with 10-million-degree plasma detected by Chandra. This spatial anti-correlation between cold molecular gas and hot X-ray-emitting plasma indicates that a powerful outflow is actively displacing or heating the surrounding interstellar medium.
The energy required to maintain this cavity exceeds the output of all known stellar winds within the nuclear cluster by a significant margin. Calculations suggest that only the gravitational and accretion-driven energy of Sgr A* can account for the observed clearing. The team estimates the wind has been active for at least 20,000 years, based on the interaction between the outflow and the ionized gas streams of the Galactic Center minispiral.
This evidence of a quiescent-state outflow offers a vital data point for models of galaxy evolution, which have historically relied on observations of highly active, luminous black holes. Most supermassive black holes in the universe exist in a low-activity state similar to Sgr A*, yet their role in regulating star formation through feedback mechanisms remains poorly understood. By studying this relatively weak wind, researchers can better characterize the feedback processes that dominate the majority of cosmic history.
The detection confirms that even in its current, relatively quiet state, Sgr A* exerts a measurable influence on its immediate environment. Rebecca Diesing, a postdoctoral astrophysicist at Columbia University and the Institute for Advanced Study, noted that the findings suggest Sgr A* is not an outlier among supermassive black holes. The study provides a necessary empirical foundation for future investigations into how black hole feedback influences the lifecycle of molecular clouds in non-active galaxies.
Understanding this feedback loop is essential for determining how galaxies manage their gas reservoirs over billions of years. While strong winds from active galactic nuclei are known to quench star formation by sweeping gas out of the galaxy, the role of gentler winds from quiescent black holes is more nuanced. These weaker outflows may compress molecular clouds, potentially triggering localized bursts of stellar birth rather than inhibiting them.
Future research efforts will likely focus on measuring the velocity of the gas along the edges of the identified cavity to confirm the dynamics of the outflow. If subsequent ALMA observations detect shifts or wobbles in the cone’s geometry, these measurements would provide a definitive velocity profile for the wind. Such data would further clarify whether the outflow is primarily quenching star formation by clearing gas or potentially triggering localized star formation through compression.
