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Using NASA’s Chandra X-ray Observatory, astronomers found a vent attached to a “chimney” of hot gas blowing out from the center of the Milky Way galaxy. Their paper describing these results is published in The Astrophysical Journal.

Eruptions from the supermassive black hole at the center of the Milky Way, called Sagittarius A* (Sgr A* for short), may have created this chimney and vent.

The chimney and vent are about 26,000 light-years from Earth. The chimney starts at the center of the galaxy and stands perpendicular to the spiral disk of the Milky Way. Astronomers previously identified the chimney using X-ray data from Chandra and XMM-Newton, an ESA (European Space Agency) mission with NASA involvement. The radio emission detected by the MeerKAT radio telescope shows the effect of magnetic fields trapping the gas in the chimney.

The latest Chandra data reveal several X-ray ridges roughly perpendicular to the plane of the galaxy. Researchers believe these are the walls of a tunnel shaped like a cylinder that helps guide hot gas as it moves up the chimney and away from the Galactic Center. The newly discovered vent is located near the top of the chimney about 700 light-years from the galactic center.

“We suspected that the magnetic fields acted like the walls of a chimney and that hot gas moved through them like smoke,” said Scott Mackey of the University of Chicago, who led the study. “We have now found a vent near the top of the chimney.”

The team believes the vent formed when hot gas rising through the chimney hit cooler gas lying in its path. The brightness of the walls of the exhaust holes in the X-rays is caused by shock waves – similar to the sonic booms of supersonic jets – generated by this collision. The left side of the vent is likely particularly bright, as the upflowing gas hits the tunnel wall at a more direct angle and with greater force than other regions.

The study’s authors believe the hot gas most likely came from a series of events involving material falling into Sgr A* and then eruptions from the black hole, sending the gas up the chimney and out the vent. However, they don’t know exactly how often the black hole is powered.

Previous studies have shown that dramatic X-ray bursts occur every few hundred years at or near the location of the central black hole, so they could play an important role in driving hot gas up through the vent. Astronomers also estimate that a galactic black hole rips apart and swallows a star every 20,000 years or so. Such events would result in powerful, explosive releases of energy, much of which would be destined to rise through the chimney openings.

“We’re not sure if this energy and heat is fueled by a large amount of material thrown onto Sgr A* all at once, like a pile of logs thrown into a fire,” said co-author Mark Morris of the University of California, Los Angeles. “Or it could come from multiple small payloads that feed into the black hole, like lighters that are regularly thrown in.”

The particles and energy in the hole provide clues to the origin of two mysterious and much larger structures around the center of the Milky Way: the Fermi bubbles observed in gamma-rays by NASA’s Fermi Gamma-ray Space Telescope and the eROSITA bubbles detected by the Newest ESA X-ray telescope. Both are pairs of structures extending thousands of light-years from the galactic center. They provide important information about past explosive activity near the center of the galaxy.

The Fermi and eROSITA bubbles are aligned with the direction of the chimney and the second X-ray chimney, which starts at the center of the galaxy and points in the opposite direction. The funnel effects of the outlet near the top of the stack can keep the hot gas focused as it moves upward, helping to form the coherent bubble structure.

“The origin of Fermi bubbles and eROSITA bubbles are one of the biggest mysteries facing the study of high-energy emission from our galaxy,” said co-author Gabriele Ponti of the Italian National Institute of Astrophysics in Merate. “We discovered a small structure that may play a big role in creating these giant bubbles.”