Astronomers spot a hot breeze from Sagittarius A*

hot breeze – Using five years of ALMA radio data and cross-checking with NASA’s Chandra X-ray observations, researchers have found a cone-shaped cavity of cold gas around Sagittarius A*, revealing a hot wind-like outflow from the Milky Way’s 1.3-trillion-Earth-mass black h

For years. scientists knew Sagittarius A* should be capable of stirring up winds—yet when they looked at the Milky Way’s own central black hole. the evidence for any gassy outflow stayed maddeningly out of reach. Now. an image built from five years of observations shows cold molecular gas sculpted into a nearly three light-years-long. cone-shaped cavity. The work. published today in Astrophysical Journal Letters. points to a black hole “breeze” that had simply been hidden until now.

Elena Murchikova of Northwestern University put it plainly when she described the surprise of the sight. “We have never seen a breeze from a black hole,” she said. “We usually see the consequences of outbursts or other violent activities.” Instead of a dramatic flare. she said she was looking at “the black hole sitting there. being quiet but still dumping energy all over the region without doing anything violent.” In her view. that combination is so unexpected it feels almost endearingly wrong-footing: “Seeing the black hole sitting there… is terribly cute. ” added Murchikova. an assistant professor in the university’s department of physics and astronomy.

At the center of our galaxy lies a black hole with a mass about 1.3 trillion times heavier than Earth. All that mass is compressed into a region just 2,000 times wider than Earth. Sagittarius A* is also the supermassive black hole suspected to lurk at the centers of all galaxies. and it has been studied intensely—so intensely. in fact. that scientists expected winds to be detectable even here. provided they were searching the right way.

But seeing a Milky Way black hole is not like observing one in a cleaner neighborhood. “To observe our own black hole. we have to look through the plane of our galaxy. ” Murchikova said in a statement. “That means we have to peer through gas. dust and ionized structures. and you can’t really see through all of that easily.” The new study tackles that obstacle by building an image of the cold molecular gas around Sagittarius A* and then stripping away the bright radio light around the black hole itself.

Murchikova and Northwestern’s Mark Gorski led a team that compiled five years of data captured by a radio telescope in Chile: the Atacama Large Millimeter/submillimeter Array. or ALMA. With those observations, they created an image of the cold molecular gas surrounding Sagittarius A*. After removing bright radio light around the black hole from the resulting image. they could see previously invisible structures inside the gas. The most striking was the cone-shaped cavity, nearly three light-years long.

To check that the cavity was not a radio-only artifact, the researchers compared it to data from NASA’s Chandra X-ray Observatory. They found the same cone-shaped void in those X-ray observations.

The shape matters because it matches the way the team suggests a wind can form near a supermassive black hole. As gas approaches Sagittarius A* closely enough to feel its gravity. it begins to heat up and orbit the black hole. The closer the gas gets, the faster it whirls—until it is moving at speeds near that of light. Trapped by the black hole’s gravitational pull. the material flattens into an accretion disk that will soon feed the black hole.

Yet, the study’s picture is not one of everything falling in. Murchikova described how radiation pressure and eruptions can push material back out. “Near black holes, the gas is subject to a lot of radiation pressure—from the same gas but … even closer to the black hole—and also various eruptions can occur in it,” she said. That outward push flings some of the hot gas into space, producing a wind. “In fact, more of the gas is ejected than falls into the black hole,” Murchikova said.

When a strong magnetic field is present, she added, the wide cone can narrow and become a jet.

The discovery lands with special weight because it resolves a specific discomfort that has lingered in the data. Murchikova said she has long found it “somewhat peculiar” that the black hole on the sky with which scientists have the most issues—and that fits theoretical expectations the worst—also happens to be our closest supermassive black hole and the one for which researchers have the most data. “This new find at least helps explain one mystery,” she said. “The lack of winds from it was one of the most obviously uncomfortable facts.”.

By showing a cone-shaped cavity in cold molecular gas around Sagittarius A*. tied to the same void in Chandra’s X-ray observations and interpreted as the imprint of a hot wind. the study supports the idea that black holes can drive such outflows—and that even our nearest heavyweight at the Milky Way’s center can be quieter than expected without being inactive.

Sagittarius A* Milky Way black hole ALMA Chandra X-ray Observatory supermassive black hole accretion disk hot wind cone-shaped cavity astrophysical journal letters