An international team of astrophysicists has made a new discovery in the center of the Milky Way galaxy. In the 1980s, Farhad Yusef-Zadeh from Northwestern University discovered one-dimensional filaments near Sagittarius A*, the galaxy’s central supermassive black hole. Yusef-Zadeh and his collaborators have now discovered a new population of filaments. These threads are shorter and lie horizontally or radially, spreading out like spokes on a wheel from the black hole. Although the two populations of filaments share similarities, Yusef-Zadeh believes they have different origins. While the vertical filaments are up to 150 light-years high and sweep through the galaxy, the horizontal filaments look more like Morse code, punctuating only one side of Sagittarius A*.
The study will be published on Friday (June 2) in The Astrophysical Journal Letters.
Yusef-Zadeh said,
“It was a surprise to suddenly find a new population of structures that seem to be pointing in the direction of the black hole. I was actually stunned when I saw these. We had to do a lot of work to establish that we weren’t fooling ourselves. And we found that these filaments are not random but appear to be tied to the outflow of our black hole. By studying them, we could learn more about the black hole’s spin and accretion disk orientation. It is satisfying when one finds order in a middle of a chaotic field of the nucleus of our galaxy.”
Yusef-Zadeh is known for uncovering mysteries at the center of our galaxy, located 25,000 light-years from Earth. The latest study builds on four decades of his research. He discovered the vertical filaments in 1984 with Mark Morris and Don Chance. Later, Yusef-Zadeh along with Ian Heywood and their collaborators discovered two gigantic radio-emitting bubbles near Sagittarius A*. Then, in a series of publications in 2022, Yusef-Zadeh (in collaborations with Heywood, Richard Arent and Mark Wardle) revealed nearly 1,000 vertical filaments, which appeared in pairs and clusters, often stacked equally spaced or side by side like strings on a harp.
Yusef-Zadeh credits the new discoveries to enhanced radio astronomy technology, particularly the South African Radio Astronomy Observatory’s (SARAO) MeerKAT telescope. To pinpoint the filaments, Yusef-Zadeh’s team used a technique to remove the background and smooth the noise from MeerKAT images in order to isolate the filaments from surrounding structures.
“The new MeerKAT observations have been a game changer. The advancement of technology and dedicated observing time have given us new information. It’s really a technical achievement from radio astronomers.”
Horizontal vs. vertical
After studying the vertical filaments for decades, Yusef-Zadeh was shocked to uncover their horizontal counterparts, which he estimates are about 6 million years old. “We have always been thinking about vertical filaments and their origin,” he said. “I’m used to them being vertical. I never considered there might be others along the plane.”
Both populations are one-dimensional filaments that can be viewed with radio waves and seem to be related to activities in the galactic center. However, they differ from each other in many ways.
The vertical filaments are magnetic and relativistic. They are perpendicular to the galactic plane and encompass particles that move at speeds close to the speed of light. On the other hand, the horizontal filaments appear to emit thermal radiation, are parallel to the galactic plane, and point towards the center of the galaxy where the black hole is located. They seem to accelerate thermal material in a molecular cloud.
There are several hundred vertical filaments but only a few hundred horizontal ones. The vertical filaments are much larger than the horizontal ones, measuring up to 150 light-years in height, while the horizontal ones are only 5 to 10 light-years long. The vertical filaments surround the nucleus of the galaxy, while the horizontal ones appear to point towards the black hole and spread only to one side.
“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.”
‘Our work is never complete’
The new discovery is filled with unknowns, and Yusef-Zadeh’s work to unravel its mysteries has just begun. For now, he can only consider a plausible explanation about the new population’s mechanisms and origins.
“We think they must have originated with some kind of outflow from an activity that happened a few million years ago. It seems to be the result of an interaction of that outflowing material with objects near it. Our work is never complete. We always need to make new observations and continually challenge our ideas and tighten up our analysis.”
