A mysterious dash is revealed in the center of the Milky Way


June 02, 2023

(Nanowerk News) An international team of astrophysicists has discovered something completely new, hidden in the center of the Milky Way galaxy.

In the early 1980s, Farhad Yusef-Zadeh of Northwestern University discovered a giant one-dimensional filament hanging vertically near Sagittarius A*, the supermassive black hole at the center of our galaxy. Now, Yusef-Zadeh and his collaborators have discovered a new population of filaments — but these threads are much shorter and lie either horizontally or radially, spreading out like the spokes of a black hole’s wheel.

Although the two filamentous populations share some similarities, Yusef-Zadeh considers the two to have a different origin. While vertical filaments sweep across the galaxy, rising 150 light-years high, horizontal filaments are more like the dots and dashes of Morse code, marking only one side of Sagittarius A*.

The study was published in Astrophysics Journal Letter (“Galactic Center Filament Population: Distribution of Position Angles Revealing Degree-Scale Collimated Outflow of Sgr A* across the Galactic Plane”). MeerKAT image of short filaments, color-coded by angle, at the center of the galaxy MeerKAT image of short filaments, color-coded by angle, at the center of the galaxy. (Image: Farhad Yusef-Zadeh)

“It’s surprising to suddenly find a population of new structures that seem to be pointing in the direction of a black hole,” said Yusef-Zadeh. “I was completely stunned when I saw this. We have to put in a lot of work to make sure that we’re not making a fool of ourselves. And we found that these filaments are not random but seem to be tied to the outflow from our black hole. By studying them, we can learn more about the orientation of the accretion disk and the black hole’s spin. It’s really satisfying when someone finds order in the chaotic field of our galactic core.”

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

This new discovery may come as a surprise, but Yusef-Zadeh is no stranger to unraveling the mysteries at the center of our galaxy, which lies 25,000 light years from Earth. The latest study builds on four decades of his research. After first discovering vertical filaments in 1984 with Mark Morris and Don Chance, Yusef-Zadeh along with Ian Heywood and his collaborators then discovered two giant radio emitting bubbles near Sagittarius A*. Then, in a series of publications in 2022, Yusef-Zadeh (in collaboration with Heywood, Richard Arent, and Mark Wardle) revealed nearly 1,000 vertical filaments, which appear in pairs and groups, often stacked equally spaced or side by side like the strings on a harp. .

Yusef-Zadeh commended the many new discoveries to improve radio astronomy technology, in particular the South African Radio Astronomy Observatory’s (SARAO) MeerKAT telescope. To define the filaments, Yusef-Zadeh’s team used techniques to remove the background and smooth out noise from the MeerKAT images to isolate the filaments from the surrounding structures.

“The new MeerKAT observations have been a game changer,” he said. “Technological advances and dedicated observation time have provided us with new information. This is truly a technical achievement of a radio astronomer.”

Horizontal vs vertical

After studying vertical filaments for decades, Yusef-Zadeh was surprised to find their horizontal counterparts, which he estimated were about 6 million years old. “We are always thinking about vertical filaments and their origins,” he says. “I’m used to them being vertical. I never thought there might be other people on the plane.”

Although both populations are made up of one-dimensional filaments that can be seen with radio waves and appear to be linked to activity in the galactic center, the similarities end there.

Vertical filaments are perpendicular to the galactic plane; the horizontal filaments are parallel to the plane but pointed radially toward the center of the galaxy where the black hole is located. Vertical filaments are magnetic and relativistic; horizontal filaments appear to emit thermal radiation. Vertical filaments include particles moving at speeds close to the speed of light; Horizontal filaments appear to accelerate thermal material in a molecular cloud. There are several hundred vertical filaments and only a few hundred horizontal filaments. And vertical filaments, which reach 150 light years in height, far exceed the size of horizontal filaments, which are only 5 to 10 light years in length. Vertical filaments also dot the space around the galactic core; Horizontal filaments appear to spread only to one side, leading toward the black hole.

“One of the most important implications of the radial outflows that we have detected is the orientation of the accretion disk and the outflow driven jets from Sagittarius A* along the galactic plane,” said Yusef-Zadeh.

‘Our work is never done’

This new discovery is filled with unknowns, and Yusef-Zadeh’s job to unravel its mystery is just beginning. For now, he could only consider plausible explanations for the mechanisms and origins of the new population.

“We think they must have come from some sort of outflow of activity that occurred several million years ago,” Yusef-Zadeh said. “It appears to be the result of the outgoing material interacting with nearby objects. Our work is never finished. We always need to make new observations and continue to challenge our ideas and refine our analysis.”


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