Researchers say they have solved a decades-old puzzle about Sagittarius A*, the supermassive black hole at the center of the Milky Way. A study from Northwestern University, published in The Astrophysical Journal Letters, found evidence of a faint, hot outflow, or “cosmic wind,” showing the black hole is not inert, but still active in a subtle way.
Sagittarius A* is about 4 million times the mass of the Sun, and it has puzzled astronomers since the 1970s because it appeared unusually quiet compared with other black holes. Using radio observations from ALMA and X-ray data from NASA’s Chandra telescope, researchers Mark Gorsky and Lena Murchikova built a detailed map of gas around the black hole and identified a cone-shaped cavity in the surrounding cold gas.
Gorsky compared the effect to “a hair dryer,” saying the wind pushes warm, turbulent gas into dense, cold material, moving and heating it without blasting it out of the system. To confirm the finding, the team removed background noise from the most detailed map of the region and found a strong match between the hot area and the void in the cold gas, indicating direct black hole activity.
The study also suggests black holes can launch winds even during low-activity periods, not only during rapid growth phases. Because Earth’s view of the galactic center is obscured by gas and dust, the work may help scientists better understand how Sagittarius A* regulates its growth and the energy in the galaxy. The team now plans to expand the gas mapping and create a “movie” of gas moving toward the black hole to measure how much material it consumes over time. Yale’s Priyamvada Natarajan said the researchers have given the field “a new observational tool,” adding that follow-up studies should be “rich and fascinating.”
