The Milky Way’s Central Black Hole Gives Radio Astronomers a Surprise

Astronomers have detected a new set of whiskers on the black hole at the center of our Milky Way galaxy: filaments of radio energy a few light-years long, and streaming outward along the galactic plane.

The streaks may be the fading remains of explosive outbursts from the black hole, Sagittarius A*, which contains the mass of 4 million suns, according to Farhad Yusef-Zadeh of Northwestern University.

Dr. Yusef-Zadeh led a team of radio astronomers that studied Sagittarius A* with the MeerKAT telescope, the South African Radio Astronomy Observatory’s sprawling array of antennas. They published their results on June 2 in The Astrophysical Journal Letters.

The discovery adds a new dimension to the electrical complexity of the Milky Way. In its structure, the galaxy resembles a sunny-side-up egg, with a bulbous, bright middle surrounded by a flat disk of stars, gas and dust.

Dr. Yusef-Zadeh, a dedicated explorer of the galaxy’s heart of darkness, and his colleagues had already detected radio filaments, thin magnetic tubes of energy 150 light-years long, running perpendicular to the galactic plane like the pickets of a fence.

The new filaments are shorter — a few light-years in length — and they run in a different direction, parallel to the galactic plane rather than through it. “It was a surprise to suddenly find a new population of structures that seem to be pointing in the direction of the black hole,” Yusef-Zadeh said in a news release issued by Northwestern University. “I was actually stunned when I saw these.”

He added in an email: “The filaments show up nicely once you know what you are looking for. It was an awe moment for us to realize these filaments were pointing toward the black hole.”

The geometry of the new streaks suggests that the black hole is spinning on an axis that is likewise parallel to the plane, Dr. Yusef-Zadeh added. The energy is squeezed out from the poles like toothpaste from a tube. Astronomers still do not know what the perpendicular vertical filaments are, he said.

Future observations with the Event Horizon Telescope, the far-flung network of Earthbound observation posts that in 2022 produced the first image of Sagittarius A*, should shed further light on the behavior and orientation of the black hole, Dr. Yusef-Zahed said. He added: “It is satisfying when one finds order in the middle of a chaotic field of the nucleus of our galaxy.”