Streamlines showing magnetic fields layered over a color image of the dusty ring around the Milky Way’s massive black hole. The Y-shaped structure is warm material falling toward the black hole, which is located near where the two arms of the Y-shape intersect. The streamlines reveal that the magnetic field closely follows the shape of the dusty structure. Each of the blue arms has its own field that is totally distinct from the rest of the ring, shown in pink.

Behold, the latest image from NASA’s Stratospheric Observatory for Infrared Astronomy, SOFIA, overlaid on a Hubble Space Telescope image of the center of the Milky Way galaxy, showing the gigantic magnetic fields that are apparently keeping the black hole at its heart from gobbling up our entire galaxy.

Supermassive black holes exist at the center of most galaxies, and our Milky Way is no exception. But many other galaxies have highly active black holes, meaning a lot of material is falling into them, emitting high-energy radiation in this “feeding” process. The Milky Way’s central black hole, on the other hand, is relatively quiet. New observations from NASA’s Stratospheric Observatory for Infrared Astronomy, SOFIA, are helping scientists understand the differences between active and quiet black holes.

These results give unprecedented information about the strong magnetic field at the center of the Milky Way galaxy. Scientists used SOFIA’s newest instrument, the High-resolution Airborne Wideband Camera-Plus, HAWC+, to make these measurements.

“This is one of the first instances where we can really see how magnetic fields and interstellar matter interact with each other,” noted Joan Schmelz, Universities Space Research Center astrophysicist at NASA Ames Research Center in California’s Silicon Valley, and a co-author on a paper describing the observations.  “HAWC+ is a game-changer.”

Previous observations from SOFIA show the tilted ring of gas and dust orbiting the Milky Way’s black hole, which is called Sagittarius A* (pronounced “Sagittarius A-star”). But the new HAWC+ data provide a unique view of the magnetic field in this area, which appears to trace the region’s history over the past 100,000 years.

Details of these SOFIA magnetic field observations were presented at the June 2019 meeting of the American Astronomical Society and will be submitted to the Astrophysical Journal.

The gravity of the black hole dominates the dynamics of the center of the Milky Way, but the role of the magnetic field has been a mystery. The new observations with HAWC+ reveal that the magnetic field is strong enough to constrain the turbulent motions of gas. If the magnetic field channels the gas so it flows into the black hole itself, the black hole is active, because it is eating a lot of gas. However, if the magnetic field channels the gas so it flows into an orbit around the black hole, then the black hole is quiet because it’s not ingesting any gas that would otherwise eventually form new stars.