The supermassive black hole at the center of the galaxy has revealed one of its best-kept secrets

After five decades of trying, astronomers have finally detected the wind emitted by the supermassive black hole at the center of the Milky Way, the galaxy in which our solar system is located, although it turns out to be more of a gentle breeze than a hurricane, writes Reuters.

Using data from Chile's ALMA radio telescope and NASA's orbiting Chandra X-ray Observatory, researchers observed the black hole's cosmic neighborhood — called Sagittarius A*, or Sgr A* for short.

They identified a vast conical cavity filled with hot ionized gas adjacent to Sgr A*, which they concluded was shaped by a wind from the black hole, which removed or heated the cold gas that previously occupied the region.

The researchers showed that the energy needed to create such a cavity can only be generated by a supermassive black hole.

Almost every galaxy has a supermassive black hole at its center

Black holes are extraordinarily dense objects with such strong gravity that even light cannot escape once it passes a certain point in their gravitational field. Galaxies typically have a supermassive black hole at their center, which pulls in gas and other material from its surroundings.

Scientists assumed decades ago that any active supermassive black hole, by the nature of its physical processes, should expel some of its gas and other material into space—either as an outward-propagating wind or as a jet.

They later identified this phenomenon in numerous supermassive black holes in other galaxies, but so far had not been able to demonstrate that Sgr A* does the same.

“This discovery solves a half-century-old mystery,” said Lena Murchikova, a professor of physics and astronomy at Northwestern University and lead author of the study published this week in the Astrophysical Journal Letters.

A “gentle breeze” in the middle of the Milky Way

Sgr A* has a mass about 4 million times that of the Sun and is about 26,000 light-years from Earth. A light-year is the distance light travels in one year, which is about 9.5 trillion kilometers. The black hole is not as massive as some of those discovered at the center of other galaxies and is currently in a relatively quiet phase.

The tip of the cone-shaped cavity starts in the immediate vicinity of Sgr A* and extends outwards. Although the researchers are unsure of the exact size of the cavity because it is beyond their field of observation, Murchikova said it could be about 6.5 light-years across.

Because of Sgr A*'s current quiescent state, the winds it generates are not as intense as those seen with other supermassive black holes. Astronomer Mark Gorski from Northwestern University, coordinator of the study, compared these winds to meteorological phenomena on Earth.

“It's a light breeze from our supermassive black hole. It doesn't seem strong enough to drastically restructure the galactic center,” he says.

“Supermassive black holes spend most of their time in this quiet and gentle state. However, they sometimes go through episodes of activity that range from ordinary storms to the most violent hurricanes. Their most intense winds or jets can completely disrupt their host galaxies and regions far beyond,” explains Gorski.

How black holes end up emitting jets of material

As gas and other material are drawn inward into a black hole, they reach speeds close to the speed of light, generating enough energy and pressure to eject some of the matter outward.

“While some of the gas continues to fall into the hole, another part is ejected. In fact, more gas is ejected than falls into the black hole. This ejected gas is the wind we are talking about,” Murchikova also explains.

“When we look at distant galaxies, it's much easier to see violent phenomena. We see huge, powerful jets tearing through the galaxy and everything in their path. We see violent winds ejecting almost all the gas from those galaxies,” she adds.

The difference between a jet and a wind is purely geometric.

“Jets are narrow and don't widen much as they move away from their source, often producing a beam of matter. Winds, on the other hand, are wider and expand as they leave the source. It's almost like the difference between a flashlight and the point of light produced by a laser,” concludes Gorski.