New radio telescope images show hundreds of one-dimensional filaments spreading like spokes on a wheel from the Milky Way’s central supermassive black hole – Sagittarius A*.
The finding comes after Northwestern University astronomy and physics professor Farhad Yusef-Zadeh’s 1984 discovery of longer filaments – unusual formations of cosmic ray electrons – dangling vertically (perpendicular to the galactic plane) near the black hole. It is believed that these structures are related to and amplify a strong magnetic field near the centre of the galaxy.
“I’m used to them being vertical,” Yusef-Zadeh says. “I never considered there might be others along the plane.”
In the 1980s, Yusef-Zadeh found that the nearly 1,000 vertical filaments appeared in pairs and clusters near Sagittarius A*, often equally spaced like guitar strings.
While the two filament populations share many features, Yusef-Zadeh believes they have different origins.
While the vertical filaments found in the ’80s pierce through the galaxy and can be up 150 light years in length, the newly-discovered horizontal filaments are found on only one side of Sagittarius A*. Yusef-Zadeh says the horizontal filaments are 5–10 light-years long.
“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 says.
“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’s team used the South African Radio Astronomy Observatory’s MeerKAT telescope to find the filaments. They removed background noise from MeerKAT images to isolate them from surrounding structures.
While the much longer vertical filaments are magnetic and made from [or made up of] particles moving near the speed of light, the horizontal filaments emit thermal radiation and appear to accelerate thermal material in a molecular cloud. An analysis of the material that the horizontal filaments are accelerating places them at about six million years old according to Yusef-Zadeh.
The horizontal filaments appear to spread out from only on one side of Sagittarius A* – pointing toward the central supermassive black hole – which suggests the filaments have connection to the black hole’s processes.
“We think they must have originated with some kind of outflow from an activity that happened a few million years ago,” Yusef-Zadeh says.
“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.”