NASA's Chandra Notices the Galactic Center is Venting

Image of a region near the center of our galaxy that shows the vent and chimney features.
Galactic Center Vent
Credit: X-ray: NASA/CXC/Univ. of Chicago/S.C. Mackey et al.; Radio: NRF/SARAO/MeerKAT; Image Processing: NASA/CXC/SAO/N. Wolk

These images show evidence for an exhaust vent attached to a chimney releasing hot gas from a region around the supermassive black hole at the center of the Milky Way, as reported in our latest press release. In the main image of this graphic, X-rays from NASA’s Chandra X-ray Observatory (blue) have been combined with radio data from the MeerKAT telescope (red).

Previously, astronomers had identified a “chimney” of hot gas near the Galactic Center using X-ray data from Chandra and ESA’s XMM-Newton. Radio emission detected by MeerKAT shows the effect of magnetic fields enclosing the gas in the chimney.

The evidence for the exhaust vent is highlighted in the inset, which includes only Chandra data. Several X-ray ridges showing brighter X-rays appear in white, roughly perpendicular to the plane of the Galaxy. Researchers think these are the walls of a tunnel, shaped like a cylinder, which helps funnel hot gas as it moves upwards along the chimney and away from the Galactic Center.

A labeled version of the image gives the locations of the exhaust vent, the chimney, the supermassive black hole at the center of the Milky Way Galaxy (called Sagittarius A*, or Sgr A* for short) and the plane of the galaxy.

Region Near the Milky Way's Galactic Center (Labeled)
Region Near the Milky Way's Galactic Center (Labeled). Credit: X-ray: NASA/CXC/Univ. of Chicago/S.C. Mackey et al.; Radio: NRF/SARAO/MeerKAT; Image Processing: NASA/CXC/SAO/N. Wolk

This newly discovered vent is located near the top of the chimney about 700 light-years from the center of the Galaxy. To emphasize the chimney and exhaust vent features the image has been rotated by 180 degrees from the conventional orientation used by astronomers, so that the chimney is pointed upwards.

The authors of the new study think that the exhaust vent formed when hot gas rising through the chimney struck cooler gas lying in its path. The brightness of the exhaust vent walls in X-rays is caused by shock waves — similar to sonic booms from supersonic planes — generated by this collision. The left side of the exhaust vent is likely particularly bright in X-rays because the gas flowing upwards is striking the tunnel wall at a more direct angle and with more force than other regions.

The researchers determined that the hot gas is most likely coming from a sequence of events involving material falling towards Sgr A*. They think eruptions from the black hole then drove the gas upwards along the chimneys, and out through the exhaust vent.

It is unclear how often material is falling onto Sgr A*. Previous studies have indicated that dramatic X-ray flares take place every few hundred years at or near the location of the central black hole, so those could play important roles in driving the hot gas upwards through the exhaust vent. Astronomers also estimate that the Galactic black hole rips apart and swallows a star every 20,000 years or so. Such events would lead to powerful, explosive releases of energy, much of which would be destined to rise through the chimney vent.

The paper describing these results is published in The Astrophysical Journal and a preprint is available online. The authors of the paper are Scott Mackey (University of Chicago), Mark Morris (University of California, Los Angeles), Gabriele Ponti (Italian National Institute of Astrophysics in Merate ), Konstantina Anastasopoulou (Italian National Institute of Astrophysics in Palermo), and Samaresh Mondal (Italian National Institute of Astrophysics in Merate).

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