After searching for 50 years, astronomers have finally discovered evidence of powerful winds blowing from Sagittarius A* (Sgr A*), the supermassive black hole at the heart of our galaxy. The discovery represents a deepening of our understanding of the physics at play both around supermassive black holes and at the heart of the Milky Way.

Scientists have long proposed that black holes produce energy as they consume matter that pushes material away from their vicinity, a process which has been dubbed "black hole winds." That even applies to Sgr A*, which exists on a diet of gas and dust so meager For a human, the equivalent would be consuming one grain of rice every million years.

The problem is, scientists have been unable to collect evidence of black hole winds blowing through the heart of the Milky Way, resulting in a mystery that has persisted in astronomy for around half a century — that is, until now.

"Unless a black hole exists in a perfect vacuum, it must blow a wind somehow. And there is no perfect vacuum in the universe," team co-leader and Northwestern University researcher Mark Gorski said in a statement. "With new observations, this is the first time we’ve had a clean enough view to see the wind's imprint. We looked at the data and said, 'There it is. There is the thing that everybody’s been looking for for 50 years.'"

Seeing black hole winds is far from a breeze

Scientists have been aware for some time that feeding black holes launch powerful outflows of material around them, including jets and winds. Winds are caused when matter falling to the black hole is accelerated to near light-speed, generating pressure that pushes infalling material away. That has been seen with ravenously feeding black holes before, but not the barely feeding Sgr A*. Its sparse consumption of material and the fact it is obscured by the plane of the Milky Way from our vantage point have made tracing this wind difficult.

Gorski's Northwestern colleague and team co-leader Lena Murchikova pointed out that the scientists were the first to detect molecular gas very close to Sgr A* feeding the supermassive black hole. That makes Sgr A* reassuringly like other supermassive black holes.

"The wind is not powerful, and its direction probably wanders with time. It shows that our black hole is not unique, and our place in the universe is not unique," Murchikova added. "To observe our own black hole, we have to look through the plane of our galaxy. That means we have to peer through gas, dust and ionized structures, and you can’t really see through all of that easily.”

To tackle these difficulties, the team turned to five years of deep observations of the heart of the Milky Way collected by the Atacama Large Millimeter/Submillimeter Array (ALMA), 66 radio antennas located in northern Chile. This delivered the sharpest image yet of the cold molecular gas with around 3 light-years of Sgr A*.One aspect of these observations that stunned the scientists was a three-light-year-long, cone-shaped cavity in this cloud of cold gas. They reasoned that this cavity must have been cleared by hotter gas in a black hole wind sweeping through the region, either pushing the cold gas in front of it or heating the cold gas.

"If you blow hot material from the black hole, it's not going to want to exist with the cold material," Gorski said. "It's either going to push the cold material out or heat it up. And, if it's too hot, you will no longer see the cold gas."

The region around Sgr A* is packed with stars — and stars also blow winds of material from them — but the team reasons that these stellar winds would not carry enough energy to carve out such a large cavity.

"It's a huge absence of material. We calculated how much energy was needed to create this cavity. It is more than can be provided by the stars in that area," Gorski explained. "Basically, there has to be input from the supermassive black hole. And, if you follow the shape of the cone, it's pointed directly at the black hole.”

To double-check their results, the scientists turned to observations of the same region made by NASA's Chandra X-ray space telescope.

"Exceptional claims require exceptional evidence," Gorski said. "We wanted to make sure that we weren't just looking at some sort of imaging artifact. Then, the X-ray image from Chandra just slotted in perfectly. The molecular features lined up."

This backed up the results from ALMA by revealing X-ray emissions coming from the location of the cavity in the cold gas.

"When you find something that no one has seen before, the first thought that runs through your mind is not 'Oh my god, we made a discovery,'" Murchikova said. "It's 'Oh my god, what's wrong with my analysis?' But when we overlaid our image with the X-ray image, it started to make sense."

While the team's results confirm that Sgr A* is extremely quiet compared to the supermassive black holes that sit in bright, turbulent regions of other galaxies called active galactic nuclei (AGN), this black hole wind is no slouch. In fact, the scientists think that it has been raging for around 20,000 years.

"The majority of other galaxies spend most of their lives in a state where they are not particularly active," Murchikova said. "But we can only see them when they are in a fireworks stage. It is very attractive to study black holes when they are in the fireworks stage, but that’s not actually their dominant state. "Sgr A* finally gives us a window into the life of a black hole in this quiet state."

The team's research was published on Thursday (June 4) in The Astrophysical Journal Letters.

Turns out the expression "you can't have it all" also applies to black holes. Astronomers have discovered that although feeding black holes can produce powerful cosmic winds and blast out high-energy jets, they can't do both at the same time.

Instead, this new research suggests that black holes actually act like "cosmic seesaws," switching between these two distinct outflow modes. Not only does this discovery have implications for how black holes grow, but it could also help us better understand how they influence star formation, and thus how they shape their entire home galaxies.

"We're seeing what could be described as an energetic tug-of-war inside the black hole's accretion flow. When the black hole fires off a high-speed plasma jet, the X-ray wind dies down, and when the wind starts up again, the jet vanishes," team member Jiachen Jiang of the University of Warwick said in a statement. "This tells us something fundamental about how black holes regulate their energy output and interact with their surroundings."

Jiang and colleagues made this discovery while studying the system 4U 1630−472, which contains a black hole with around 10 times the mass of the sun that's actively stripping matter from a companion star. They studied this system with NASA's Neutron star Interior Composition Explorer (NICER) aboard the International Space Station (ISS) and the MeerKAT radio telescope across a period of three years.

The black hole's stolen matter forms a swirling plate of plasma around it called an accretion disk, which gradually feeds it. But not all of this ex-stellar material is destined to fall into the black hole; some is blasted away at near-light speed, while other material is blown away as black hole winds.

What the team found was this black hole never produced powerful winds and high-energy jets at the same time, even though the accretion disk and the matter stripped from the companion star restocking this disk stayed consistent.

"Our observations provide clear evidence that black hole binary systems switch between powerful jets and energetic winds — never producing both simultaneously — highlighting the complex interplay and competition between different forms of black hole outflows," team member Zuobin Zhang of the University of Oxford said in the statement.

The way outflow mechanisms seesawed for this black hole suggests a natural mechanism of self-regulation, and that jets and winds compete for the same matter. The researchers also found that though the type of outflow differed, the amount of energy and mass carried away remained consistent. That also implies a roughly steady total rate of outflow.

The team behind this research theorizes that the switch-in-outflow method doesn't hinge on how much matter is falling toward the black hole, but on the configuration of the magnetic fields within the accretion disk.

That means black holes don't just gobble up gas and dust in their host galaxies, but can also manage how this matter is spat back into their cosmic environment. As this gas and dust are the building blocks of new stars, this means these cosmic seesaws play a crucial role in regulating star formation and therefore the growth of galaxies.

The team's research was published on Jan. 5 in the journal Nature Astronomy.

Hot gas streaming out from the region around supermassive black holes can experience rapid and extreme changes in temperature, according to observations from NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) telescope.

Supermassive black holes are thought to be embedded in the middle of most large galaxies, including the Milky Way. These monsters feed from a surrounding disk of gas, dust and other material, called an accretion disk. The gravitational pull of the black hole can heat up material in the accretion disk, causing it to radiate light.

Young and energetic black holes can gobble up only so much material, however, before the feeding process produces hot streams of gas from the accretion disk. These black-hole winds travel at about a quarter of the speed of light, and have the potential to disturb star formation in their wake.[Strangest Black Holes in the Universe]

Using NuSTAR and the European Space Agency's XMM-Newton telescope, scientists have for the first time observed winds from a nearby black hole interacting with radiation coming from the black hole's edge, according to the authors of a study.

Harrison's team wanted to learn about the temperatures of these winds, so they looked at X-rays coming from the black hole's edge. As the X-rays pass through the winds, chemical elements present in the winds — such as iron and magnesium — absorb some wavelengths of light in the X-ray spectrum. The spectrum then displays holes, also called "absorption features," revealing more about the wind's composition.

"While observing this spectrum, the team noticed that the absorption features were disappearing and reappearing in the span of a few hours," according to a statement from the California Institute of Technology (Caltech). "The team concluded that the X-rays were actually heating up the winds to very high temperatures — millions of degrees Fahrenheit — such that they became incapable of absorbing any more X-rays. The winds then cool off, and the absorption features return, starting the cycle over again."

Being able to study the properties of these winds offers scientists an opportunity to learn more about how those winds impact the evolution of galaxies.

"We know that supermassive black holes affect the environment of their host galaxies, and powerful winds arising from near the black hole may be one means for them to do so," Fiona Harrison, NuSTAR principal investigator and a physics and astronomy professor at Caltech, said in the statement. "The rapid variability, observed for the first time, is providing clues as to how these winds form, and how much energy they may carry out into the galaxy."

The researchers are planning to conduct more observations to learn how the winds are formed, where their source of power is from and how long they last, among other features. The findings will be published tomorrow (March 2) in the journal Nature.

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The intense energy and winds from gigantic black holes can block the birth of stars as scientists have long suspected, a new analysis of distant galaxies reveals.

Most galaxies, including our own Milky Way, are thought to have supermassive black holes at their hearts. Some of these monster black holes are relatively calm, but others, known as "active galactic nuclei," or AGN, can spew out more radiation than our entire galaxy does, and from a patch of space no larger than our solar system.

Scientists had long thought all this energy from active galactic nuclei quenched the formation of stars around them.

"There is so much energy in the radiation coming out from the AGNs, that if the surrounding gas absorbs just a small fraction — about one-twentieth will do it — it will have enough energy to escape from the host galaxy, and effectively becomes a wind clearing the galaxy of gas," said study lead author Mathew Page, an astrophysicist at University College London. "Once the gas has been heated up and driven out, there's no material from which to form stars." [Gallery: Black Holes of the Universe]

Proving whether this star-stifling occurs has been a problem because measuring star formation in galaxies containing powerful active galactic nuclei has long been difficult. The radiation from these jumbo black holes outshines that from star formation in nearly all wavelengths of light.

The best chance to find this evidence lies in the far-infrared to millimeter wavelengths of the electromagnetic spectrum, since active galactic nuclei emit comparatively little radiation at these wavelengths.

In the new study, scientists combined observations of far-infrared to millimeter wavelengths, which shed light on star formation, with those of X-rays, which are clear signs of active galactic nuclei, to help show these supermassive black holes apparently do suppress star formation.

"Even though the black hole is little more than a speck in size compared to the galaxy, basically that speck controls the fate of the whole galaxy," Page told SPACE.com.

The research is detailed in tomorrow's (May 10) issue of the journal Nature.

Submillimeter observations from the Herschel Space Observatory revealed that rapid star formation was common in the host galaxies of active galactic nuclei when the universe was 2 billion to 6 billion years old. However, X-ray observations from the Chandra X-ray Observatory showed that vigorous star formation was not seen around black holes that had X-ray luminosities of 10^44 ergs per second. (An erg is a unit of energy, and 10^44 is short for a 1 with 44 zeroes behind it.)

"10^44 ergs per second is about 25 billion times the luminosity of the sun; it is about 10 times the luminosity of the Milky Way," Page said. "But this is only the luminosity of the active galactic nucleus in X-rays — it will radiate about 20 times as much power over the rest of the electromagnetic spectrum."

All this energy should be enough to drive powerful outflows of gas, stripping the areas around the black holes of stellar construction materials.

Future research can focus on "catching some galaxies as they're actually going through the stage of having their star formation switched off, rather than seeing them before or after, as we do for most of the objects we've looked at here," Page said. "The biggest obstacle to that is the need to have infrared and X-ray observatories in space. A successor to the Chandra and XMM-Newton X-ray observatories is what I'd like."

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Scientists have measured the fastest winds yet observed from a stellar-mass black hole, shedding light on the behavior of these curious cosmic objects.

The winds, clocked by astronomers using NASA's Chandra X-ray Observatory, are racing through space at 20 million mph (32 million kph), or about 3 percent the speed of light. That's nearly 10 times faster than had ever been seen from a stellar-mass black hole, researchers said.

"This is like the cosmic equivalent of winds from a Category 5 hurricane," study lead author Ashley King, of the University of Michigan, said in a statement. "We weren't expecting to see such powerful winds from a black hole like this."

A stellar-mass black hole, which is born when an extremely massive star collapses, typically contains about five to 10 times the mass of our sun. The stellar-mass black hole powering this super wind is known as IGR J17091-3624, or IGR J17091 for short. [Photos: Black Holes of the Universe]

IGR J17091 is a binary system in which a sun-like star orbits a black hole. It's found in the central bulge of our Milky Way galaxy, about 28,000 light-years from Earth.

IGR J17091's wind matches some of the fastest generated by supermassive black holes, which are millions or billions of times more massive. Supermassive black holes are thought to reside at the heart of most if not all active galaxies, including our own Milky Way.

"It's a surprise this small black hole is able to muster the wind speeds we typically only see in the giant black holes," said co-author Jon Miller, also from the University of Michigan. "In other words, this black hole is performing well above its weight class."

Another surprising finding from the new study is that the wind, which comes from a disk of gas surrounding the black hole, may be blasting more material into space than the black hole is capturing.

"Contrary to the popular perception of black holes pulling in all of the material that gets close, we estimate up to 95 percent of the matter in the disk around IGR J17091 is expelled by the wind," King said.

Unlike hurricane winds on Earth, the wind from IGR J17091 is blowing in many different directions at once. This pattern distinguishes it from a jet, in which material flows in focused beams perpendicular to a black hole's disk, often at nearly the speed of light.

Jets have been seen coming from IGR J17091 before. But observations made with the National Radio Astronomy Observatory's Expanded Very Large Array in New Mexico showed that a radio jet from the system was not present when the super-fast wind was blowing.

This agrees with observations of other stellar-mass black holes, suggesting that ultra-speedy winds can quash jet production, researchers said.

Scientists estimated IGR J17091's wind speeds using a spectrum made by Chandra in 2011. Observations made by the space telescope two months earlier showed no such winds, meaning the black hole's gale likely switches on and off over time.

Astronomers think that magnetic fields in the accretion disks of black holes are responsible for producing both winds and jets. Characteristics of the magnetic fields and the rate at which material falls toward the black hole are thought to determine whether jets or winds are produced, researchers said.

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