Astronomers detected huge, one-dimensional filaments dangling vertically around Sagittarius A*, our galaxy’s center supermassive black hole, in the early 1980s. Astronomers have identified a new population of filaments, but these threads are much shorter and lie horizontally or radially, extending out from the black hole like spokes on a wheel.
A multinational team of astrophysicists has uncovered something completely new in the Milky Way galaxy’s core.
Farhad Yusef-Zadeh of Northwestern University discovered huge, one-dimensional filaments dangling vertically around Sagittarius A*, our galaxy’s center supermassive black hole, in the early 1980s. Yusef-Zadeh and his colleagues have identified a new population of filaments, but these threads are much shorter and lie horizontally or radially, extending out from the black hole like spokes on a wheel.
One of the most important implications of radial outflow that we have detected is the orientation of the accretion disk and the jet-driven outflow from Sagittarius A* along the galactic plane.Yusef-Zadeh
Although the two filament populations share many features, Yusef-Zadeh believes they originated in distinct places. While the vertical filaments span the galaxy, soaring up to 150 light-years in height, the horizontal filaments resemble Morse code dots and dashes, punctuating only one side of Sagittarius A*.
The study is published in The Astrophysical Journal Letters.
“It was unexpected to find a new population of structures pointing in the direction of the black hole,” Yusef-Zadeh added. “I was truly taken aback when I saw these. We had to put in a lot of effort to prove that we weren’t delusory. And we discovered that these filaments are not random but appear to be linked to our black hole’s outflow. We could learn more about the black hole’s spin and accretion disk orientation by analyzing them. It’s wonderful to discover order in the midst of our galaxy’s tumultuous nucleus.”
An expert in radio astronomy, Yusef-Zadeh is a professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of CIERA.
Decades in the making
The unexpected discovery may come as a surprise, but Yusef-Zadeh is no stranger to solving puzzles at the heart of our galaxy, which is roughly 25,000 light-years away from Earth. His most recent study relies on four decades of research. Yusef-Zadeh, together with Ian Heywood and their partners, discovered two massive radio-emitting bubbles around Sagittarius A* after first identifying the vertical filaments in 1984 with Mark Morris and Don Chance. Then, in a series of papers published in 2022, Yusef-Zadeh (in collaboration with Heywood, Richard Arent, and Mark Wardle) discovered approximately 1,000 vertical filaments that formed in pairs and clusters, often piled equally spaced or side by side like harp strings.
Yusef-Zadeh attributes the rush of new findings to improved radio astronomy technology, specifically the MeerKAT telescope at the South African Radio Astronomy Observatory (SARAO). Yusef-Zadeh’s team employed a technique to remove background and smooth noise from MeerKAT photos in order to isolate the filaments from surrounding structures in order to localize the filaments.
“The new MeerKAT observations have been a game changer,” he explained. “Technology advancement and dedicated observation time have provided us with new information.” It’s a true technological accomplishment by radio astronomers.”
Horizontal vs. vertical
Yusef-Zadeh was astounded to discover horizontal counterparts to the vertical strands, which he estimates are roughly 6 million years old. “We’ve always been interested in vertical filaments and their origin,” he explained. “I’m used to seeing them vertically. I never considered that there could be others on the plane.”
While both populations are made up of one-dimensional filaments that may be seen with radio waves and appear to be linked to galactic center activity, the similarities end there.
The vertical filaments are perpendicular to the galactic plane; the horizontal filaments are parallel to the plane but point radially toward the center of the galaxy where the black hole lies. The vertical filaments are magnetic and relativistic; the horizontal filaments appear to emit thermal radiation. The vertical filaments encompass particles moving at speeds near the speed of light; the horizontal filaments appear to accelerate thermal material in a molecular cloud. There are several hundred vertical filaments and just a few hundred horizontal filaments. The vertical filaments, which measure up to 150 light-years high, far surpass the size of the horizontal filaments, which measure just 5 to 10 light-years in length. The vertical filaments also adorn space around the nucleus of the galaxy; the horizontal filaments appear to spread out to only one side, pointing toward the black hole.
“One of the most important implications of radial outflow that we have detected is the orientation of the accretion disk and the jet-driven outflow from Sagittarius A* along the galactic plane,” Yusef-Zadeh said.
‘Our work is never complete’
The new discovery is riddled with mystery, and Yusef-Zadeh’s work to solve them has only just begun. For the time being, he can only explore a feasible explanation for the mechanisms and origins of the new population.
“We think they must have originated with some kind of outflow from an activity that happened a few million years ago,” Yusef-Zadeh explained. “It appears to be the result of that outflowing material interacting with objects nearby.” Our task is never finished. We must constantly make new observations, test our notions, and tighten our analyses.”