Sagittarius A*: Detection of Hot Gas Emitted from a Black Hole Confirmed

Researchers have confirmed that hot winds are emanating from the supermassive black hole at the center of the Galaxy for the first time.

In contrast to many other supermassive black holes throughout the universe, Sagittarius A* (SGR A*) remains relatively subdued. Unlike its more active counterparts that emit vast jets, SGR A* does not produce such striking displays. While many supermassive black holes create winds, which are streams of hot gas that originate near the event horizon, these have never been definitively observed around SGR A*, despite theoretical predictions dating back to the 1970s.

Mark Golsky and Elena Marchikova from Northwestern University, Illinois, utilized the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to conduct a more detailed study of the cold gas in the innermost region of the Circumnuclear Disk (CND). Their observations revealed an unexpectedly large volume of cold gas and a distinct cone that penetrates through the hot gas.

“To find such a significant amount of cold gas so close to the black hole was surprising,” says Golsky. “Conventional understanding suggested it was unlikely to be there, which is why we hadn’t previously searched for it. When I shared this image, my colleague remarked, ‘We need to investigate this further, as it’s been a puzzle for over 50 years.’”

Golsky and Marchikova’s five years of observations provided a detailed analysis of the innermost part of the CND, mapping cold gases within a vicinity of SGR A* 100 times previous measurements. By simulating and subtracting the bright variability of SGR A*, they could isolate the dim light from the cold gas.

This approach revealed a pronounced cone region nearly devoid of cold gas, and when they overlaid X-ray emissions (produced by the hot gas), a striking correlation emerged. The energy required to propel the hot gas through this cone approximates that of 25,000 suns—far too substantial to originate from nearby stars or supernovae, indicating it likely derives from SGR A* itself. “The energy necessary comes directly from the black hole, confirming the presence of winds originating from it,” Golsky states.

<p>Prior observations have identified expansive gas bubbles, known as Fermi bubbles, situated above and below the galaxy. However, the possibility of these jets reforming remains uncertain. Understanding this wind phenomenon sheds light on why SGR A* shows lower activity and enhances our comprehension of black hole evolution.</p>
<p>The implications of the reduced wind activity surrounding SGR A* are exciting. If verified, findings by <a href="https://scholar.google.com/citations?user=1VNwK9gAAAAJ&amp;hl=en">Ziri Younsi</a> from University College London could offer crucial insights into the nature of the black hole, including its rotational direction. Astronomers have postulated that SGR A* spins perpendicular to the Milky Way plane, implying a need for edge-on observation. However, the inaugural image of a black hole captured by the Event Horizon Telescope in 2022 produced inconclusive data, suggesting a possible in-person orientation.</p>
<p>“The mass of Sagittarius A* is well-defined by current observations, but its tilt angle relative to us remains largely unknown,” explains Younsi. “If these findings are robust, understanding the origins of these matter flows will be genuinely fascinating, as it will provide insights into how material spirals toward the black hole, contributing to our knowledge of galactic evolution.”</p>

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