These mysterious structures likely originated a few million years ago when an outflow from Sagittarius A* — a supermassive black hole in the center of our Milky Way Galaxy — interacted with surrounding material.
Color-coded position angles for all short and long radio filaments identified in the center of the Milky Way. Image credit: Yusef-Zadeh et al., doi: 10.3847/2041-8213/acd54b.
“It was a surprise to suddenly find a new population of structures that seem to be pointing in the direction of the black hole,” said Northwestern University astronomer Farhad Yusef-Zadeh.
“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.”
In the 1980s, Professor Yusef-Zadeh and colleagues discovered gigantic, one-dimensional filaments dangling vertically near Sagittarius A*.
They also uncovered two gigantic radio-emitting bubbles near the supermassive black hole.
Then, they 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.
After studying the vertical filaments for decades, Professor 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. I’m used to them being vertical. I never considered there might be others along the plane,” he said.
To pinpoint the filaments, the astronomers used a technique to remove the background and smooth the noise from the images, captured by the MeerKAT telescope at the South African Radio Astronomy Observatory (SARAO) in Cape Town, South Africa, in order to isolate the filaments from surrounding structures.
“The new MeerKAT observations have been a game changer,” Professor Yusef-Zadeh said.
“The advancement of technology and dedicated observing time have given us new information. It’s really a technical achievement from radio astronomers.”
According to the team, 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.
And 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,” Professor Yusef-Zadeh said.
A paper on the findings was published in the Astrophysical Journal Letters.
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F. Yusef-Zadeh et al. 2023. The Population of the Galactic Center Filaments: Position Angle Distribution Reveals a Degree-scale Collimated Outflow from Sgr A* along the Galactic Plane. ApJL 949, L31; doi: 10.3847/2041-8213/acd54b
