Scientists may have found the spot where our supermassive black hole “vents”

At the center of our galaxy, a supermassive black hole is blowing its top.

Astronomers had previously seen a long chimney of superheated gas trailing away from the black hole. Now, using NASA’s Chandra X-ray Observatory, they may have located the “exhaust vent.”

Scientists think these structures are created by eruptions from the supermassive black hole. The new findings are helping us understand what exactly happens around such massive black holes—including how and what they eat.

“Astrophysicists have long been interested in the movement of material and energy from the Milky Way’s center and its black hole, both to understand what’s happening in our cosmic backyard and how galaxies form and evolve,” said Scott Mackey, a scientist with the University of Chicago who led the study. “We’re really excited to find this new piece of the puzzle.”

‘Hot gas is traveling up’

It appears that nearly all galaxies have a supermassive black hole sitting at their very centers. Ours, which lives about 26,000 light-years away from Earth, is known as Sagittarius A*.

Contrary to the popular notion that black holes suck everything in, the churn near the black hole can actually mean that some of the material is blasted off at high speeds. Scientists are very interested in how much, how often, and how this happens.

To find out more, Mackey and a group of scientists peered at the galactic center using NASA’s Chandra X-ray telescope.

The telescope, located in orbit around Earth (and named after pioneering UChicago astrophysicist Subrahmanyan Chandrasekhar), is specially designed to pick up X-rays—energetic light, in very short wavelengths.

Astronomers had previously identified a “chimney” of hot material, which begins at the center of the galaxy and stands perpendicular to the Milky Way’s spiral disk. Scientists think this is a tunnel formed by the effects of strong magnetic fields circling around.

“We suspected that magnetic fields are acting as the walls of the chimney and that hot gas is traveling up through them, like smoke,” said Mackey, who is a PhD student at UChicago. “Now we’ve discovered an exhaust vent near the top of the chimney.”

The newly discovered vent is located near the top of the chimney, about 700 light-years from the center of the galaxy. This means the gas is traveling an absolutely enormous distance away from the black hole—far larger than the size of the black hole itself. It’s on the scale of an ant flinging something to the height of Mount Everest.

Black hole appetites

According to the scientists’ models, the sequence of events is something like this.

Occasionally, a star falls into the black hole. But black holes are messy eaters, and some of the material is flung away. This superheated gas travels up along the chimney at extremely high speeds, and out through the exhaust vent. Along the way, the hot gas collides with cooler gas in the chimney, creating shock waves that throw off bright X-rays—which the telescope can pick up.

However, we don’t know exactly how often the black hole is being fed.

“We’re not sure if this energy and heat are stoked by a large amount of material being dumped onto Sagittarius A* at once, like a bunch of logs being dumped on a fire,” said co-author Mark Morris of the University of California, Los Angeles. “Or it might come from multiple small loads being fed into the black hole similar to kindling being regularly tossed in.”

It’s also possible that the vent provides clues about the origin of two mysterious and much larger structures around the center of the Milky Way, known as the “Fermi Bubbles” and the “eROSITA Bubbles,” after the telescopes that discovered them.

These massive “bubbles,” full of cosmic rays and gas, may be evidence of a long-ago explosion around Sagittarius A* that was far more powerful than anything we’ve seen lately. It’s possible that in the past, our galactic center was far hungrier than it is today.

Additional study authors included Konstantina Anastasopoulou from the Italian National Institute of Astrophysics in Palermo, and Gabriele Ponti and Samaresh Mondal from the Italian National Institute of Astrophysics in Merate.

NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Citation: “X-rays from a Central "Exhaust Vent" of the Galactic Center Chimney .” Mackey et al, The Astrophysical Journal, May 10, 2024.

Funding: NASA, ESA, Istituto Nazionale di Astrofisica.

—Partly adapted from an article published by the Chandra X-ray Observatory.