We finally found the hot wind coming out of our black hole

In a groundbreaking discovery, astronomers have detected hot gas winds emanating from our galaxy’s supermassive black hole, Sagittarius A* (Sgr A*), for the first time. This finding could provide insight into the enigmatic period of inactivity exhibited by Sgr A*.

Unlike many active supermassive black holes found at the centers of other galaxies, which emit energetic jets of radiation, Sgr A* is relatively quiet. This has led to intrigue among scientists about the mechanism behind its subdued activity. Supermassive black holes are theorized to emit winds—hot gas streams that emerge from regions near their event horizons, where matter is heated drastically as it spirals inward.

Despite the anticipation surrounding these winds since the 1970s, no definitive detection had been made around Sgr A*. This is largely attributed to the complex environment surrounding the black hole, a congested mix of stars, dust, and gas forming the circumnuclear disc (CND).

Mark Gorski and Elena Murchikova from Northwestern University have utilized the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to conduct a more refined study of the CND. Their research unveiled expanses of cold gas where none were anticipated, alongside a distinct cone of hot gas that seemingly represents the elusive winds predicted in earlier models.

Gorski expressed surprise at the presence of cold gas in this area, stating, “The conventional wisdom was that there was no point searching for it as it likely didn’t exist. When I presented this image to my colleague, I said, ‘We need to focus on this, as it has been a 50-year-old problem.’”

Over the course of five years, the team gathered extensive observations of the innermost CND, achieving a resolution 100 times sharper than past studies. They modeled the variability of Sgr A*’s light and subtracted it from the faint light of the cold gas, which allowed them to identify a clear region devoid of cold gas. When overlaid with existing X-ray data—emissions stemming from hot gases—they discovered a striking correlation between the two.

Calculating the energy required to expel hot gas through this newly identified cone revealed a staggering output equivalent to approximately 25,000 solar masses. This indicates that the hot gas must originate from Sgr A* itself, dismissing other potential sources like nearby stars or supernovae. Gorski concluded, “The energy necessary implies the presence of a black hole and that it produces a wind.”

Historically, astronomers have observed enormous gas bubbles, known as Fermi bubbles, extending above and below the galactic plane, suggesting that Sgr A* may have previously emitted jets of material. However, the re-emergence of these jets remains uncertain. Understanding this newly discovered wind may aid us in deciphering Sgr A*’s inactivity and contribute to our understanding of black hole development stages.

Ziri Younsi from University College London remarked on the excitement surrounding the potential implications of this discovery. If confirmed, it might reveal critical information regarding the black hole, such as its spin direction. Astronomers have traditionally assumed that Sgr A* spins perpendicular to the Milky Way’s plane, implying that it would be seen edge-on. Yet, images captured by the Event Horizon Telescope in 2022 suggested it appeared face-on, a finding that remains inconclusive.

“Sgr A*’s mass is precisely determined, but its inclination angle is not well-constrained, making it effectively variable. Investigating the origin of matter streams, if this result proves reliable, is thrilling. It could provide vital clues regarding the direction from which material flows into the black hole,” Younsi elaborated. This research has potential implications for our broader understanding of the Milky Way’s evolution.