Here’s how magnetic fields help power a supermassive black hole

A black hole in the center of a galaxy plays a role in the galaxy’s death by eating up the surrounding dust and gas and not leaving enough matter for new stars to form. Gravity alone, however, isn’t strong enough to explain all of this material transfer.

Some theories have proposed that magnetic fields could help gravity power black holes by pushing matter in their direction. With the help of observations from the Stratospheric Observatory for Infrared Astronomy, or SOFIA, a joint project of NASA and the German Space Agency, these theories have now been confirmed. By mapping the shape of magnetic fields in the central region of NGC 1097, a spiral galaxy, the researchers found that magnetic fields help direct dust and gas towards the supermassive black hole at the center of the galaxy.

“We can, for the first time, analyze the effect of the magnetic field in gas flows to the regions [centrali] of star formation using SOFIA and the center of the galaxy using polarimetric radio observations, ”said Enrique Lopez-Rodriguez, lead author of the recent article describing the magnetic fields of NGC 1097 that was published in The Astrophysical Journal.

Artist’s impression of a supermassive black hole at the center of a galaxy

NGC 1097 has a region of intense star formation towards its center, known as the starburst ring. Since looking at magnetic fields in very dense areas is one of SOFIA’s strengths, Lopez-Rodriguez and her team used SOFIA to probe the dense regions that merge into the starburst ring. This was complemented by polarimetric radio observations within the starburst ring, a different type of astronomical observation best suited for studying scattered regions.

The researchers found a notable difference in the morphology of the magnetic fields between the two regions. SOFIA observations show the magnetic field feeding matter in the starburst ring, while polarimetric radio observations show the spiraling magnetic field in the center of the galaxy, powering the supermassive black hole.

But despite this startling difference, the two aren’t completely disconnected – the study shows that magnetic fields in the galaxy help deliver gas and dust to the black hole at its center. Overall, the large-scale fields follow the shape of NGC 1097’s spiral arms, funneling matter from the arms to the starburst ring into its innermost regions, and from the starburst ring deeper into the black hole.

This confirms that it is not only gravity that helps a black hole feed on the material in its host galaxy, but magnetic fields also play a role. “Our observations also provide evidence that magnetic fields located near black holes at the center of active galaxies could come from the large-scale magnetic field in the host galaxy,” Lopez-Rodriguez explained. This first observation of the magnetic fields that feed black holes helps answer critical questions about how galaxies evolve and eventually die.