Astronomers discover hundreds of horizontal filaments pointing towards the black hole at the center of the Milky Way

An international team of astrophysicists has discovered something entirely new, hidden in the center of the Milky Way. In the early 1980s, Farhad Yusef-Zadeh of Northwestern University discovered gigantic one-dimensional filaments hanging vertically near Sagittarius A, our galaxy’s central supermassive black hole.

Now, Yusef-Zadeh and his collaborators have discovered a new population of filaments, but these threads are much shorter and lie horizontally or radially, extending like the spokes of a wheel from the black hole.

Although the two filament populations share several similarities, Yusef-Zadeh surmises that they have different origins. While the vertical filaments sweep the galaxy and rise up to 150 light-years high, the horizontal ones are more like the dots and dashes of Morse code, punctuating only one side of Sagittarius A.

It was a surprise to suddenly find a new population of structures that seem to point in the direction of the black hole, says Yusef-Zadeh. The truth is that I was stunned when I saw them. We had to work a lot to verify that we were not fooling ourselves. And we found that these filaments are not random, but appear to be tied to the outflow from our black hole. By studying them, we were able to learn more about the spin of the black hole and the orientation of the accretion disk. It’s satisfying when one finds order in the midst of a chaotic field at the core of our galaxy.

An expert in radio astronomy, Yusef-Zadeh is Professor of Physics and Astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of CIERA.

The new discovery may come as a surprise, but Yusef-Zadeh is no stranger to uncovering mysteries at the center of our galaxy, located 25,000 light-years from Earth. The latest study builds on four decades of research. After first discovering vertical filaments in 1984 with Mark Morris and Don Chance, Yusef-Zadeh along with Ian Heywood and collaborators later discovered two gigantic radio-emitting bubbles near Sagittarius A. Subsequently, in a series of 2022 posts , Yusef-Zadeh (in collaboration with Heywood, Richard Arent and Mark Wardle) revealed nearly 1,000 vertical filaments, appearing in pairs and clumps, often stacked equally spaced apart or next to each other like the strings of a harp.

Yusef-Zadeh attributes the spate of new discoveries to improving radio astronomy technology, in particular the South African Radio Astronomy Observatory’s (SARAO) MeerKAT telescope. To locate the filaments, Yusef-Zadeh’s team used a technique to remove background and smooth noise from the MeerKAT images to isolate the filaments from surrounding structures.

The new MeerKAT observations have been a game changer, he said. The advancement of technology and the dedicated observation time have provided us with new information. It is really a technical achievement of radio astronomers.

After studying vertical filaments for decades, Yusef-Zadeh was surprised to discover his horizontal counterparts, which he estimates are about 6 million years old. We have always thought about vertical filaments and their origin, he explains. I’m used to them being vertical. I had never considered that there might be others along the plane.

Although both populations comprise one-dimensional filaments that can be seen with radio waves and appear to be linked to activities at the galactic center, the similarities end there.

The vertical filaments are perpendicular to the galactic plane; the horizontal ones are parallel to the plane but point radially towards the center of the galaxy, where the black hole is located. The vertical filaments are magnetic and relativistic; the horizontal ones seem to emit thermal radiation. The vertical filaments encompass particles that move at speeds close to the speed of light; the horizontal filaments appear to accelerate thermal material into a molecular cloud. There are several hundred vertical filaments and only a few hundred horizontal filaments. And the vertical filaments, which are up to 150 light-years tall, far exceed the size of the horizontal filaments, which are only 5 to 10 light-years long. Vertical filaments also grace the space around the galaxy’s core; the horizontal ones appear to extend to only one side, pointing toward the black hole.

One of the most important implications of the radial outflow we have detected is the orientation of the accretion disk and jet-driven outflow of Sagittarius A along the galactic plane, Yusef-Zadeh said.

The new discovery is full of unknowns, and Yusef-Zadeh’s work to unravel the mysteries of it has only just begun. For now, he can only consider a plausible explanation for the mechanisms and origins of the new population.

We think they must have originated with some sort of outflow from activity that occurred a few million years ago, Yusef-Zadeh said. It appears to be the result of an interaction of that outgoing material with nearby objects. Our work is never complete. We always need to make new observations and continually question our ideas and refine our analyses.

Northwestern University | F. Yusef-Zadeh, R.G. Arendt, et al., The Population of the Galactic Center Filaments: Position Angle Distribution Reveals a Degree-scale Collimated Outflow from Sgr A along the Galactic Plane. The Astrophysical Journal Letters, vol.949, no.2. DOI 10.3847/2041-8213/acd54b