At the center of the Milky Way, there is a supermassive black hole 4.6 million times the mass of the Sun called Sagittarius A*. Some supermassive black holes end up in a feeding frenzy, gobbling material and emitting intense radiation that can affect a whole galaxy, but not Sagittarius A*. Researchers now think they have uncovered the reason why certain supermassive black holes are quiet.
Brand new observations of the gas and dust around the center of the galaxy have allowed researchers to work out the magnetic field around Sagittarius A*. Although gravity dominates the dynamics of the material around the black hole, this study, soon to be published in the Astrophysical Journal, shows that the magnetic fields cannot be ignored.
The observations showed a Y-shaped region around the black hole full of warm material and a larger ring-like structure spiraling inwards. Each arm of the Y has its own magnetic field and both are distinct from the wider ring. The interaction between all of them may be reducing the amount of material falling in.
“The spiral shape of the magnetic field channels the gas into an orbit around the black hole,” lead author Darren Dowell, a scientist at NASA’s Jet Propulsion Laboratory, said in a statement. “This could explain why our black hole is quiet while others are active.”
The observations were possible thanks to the high-resolution Airborne Wideband Camera-Plus, HAWC+ on NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA). When space dust is embedded in a magnetic field, molecules align in a certain way, which means the light emitted by this dust will have a certain orientation. This property, known as polarization, allowed the researchers to see the otherwise invisible magnetic field of the region.
“This is one of the first instances where we can really see how magnetic fields and interstellar matter interact with each other,” noted co-author Joan Schmelz, from a Universities Space Research Center astrophysicist at NASA Ames Research Center in California’s Silicon Valley. “HAWC+ is a game-changer.”
The research was presented at the June 2019 meeting of the American Astronomical Society.