An international team of astrophysicists has discovered hundreds of mysterious structures in the center of the Milky Way galaxy.
These one-dimensional cosmic threads are hundreds of horizontal or radial filaments—slender, elongated bodies of luminous gas that potentially originated a few million years ago when outflow from Sagittarius A*, the Milky Way’s central supermassive black hole, interacted with surrounding materials, according to a study published Friday in The Astrophysical Journal Letters. The filaments are relatively short in length, each measuring 5 to 10 light-years.
The findings come nearly 40 years after Farhad Yusef-Zadeh, the study’s lead author, and other researchers discovered another population of nearly 1,000 one-dimensional filaments, which are vertical and much larger at up to 150 light-years long each, near the galaxy’s center. Yusef-Zadeh and collaborators also found hundreds more paired and clustered vertical filaments in the same area in 2022, realizing the filaments were likely related to Sagittarius A* activity rather than bursts of supernovae, which they had previously thought. The new study both reinforces and builds upon the earlier findings.
Finding the “new population of structures that seem to be pointing in the direction of the black hole” was a surprise, Yusef-Zadeh, a professor of physics and astronomy at Northwestern University’s Weinberg College of Arts and Sciences, said in a news release.
“I was actually stunned when I saw these. We had to do a lot of work to establish that we weren’t fooling ourselves,” added Yusef-Zadeh, who’s also a member of the Center for Interdisciplinary Exploration and Research in Astrophysics. “We found that these filaments are not random but appear to be tied to the outflow of our black hole … It is satisfying when one finds order in [the] middle of a chaotic field of the nucleus of our galaxy.”
The findings related to the black hole located about 26,000 light-years from Earth are “really exciting” and “demonstrate how beautiful the universe is,” said Erika Hamden, an assistant professor of astronomy at the University of Arizona who wasn’t involved in the study.
Sagittarius A* “is the closest supermassive black hole to us, but it’s relatively quiet and therefore somewhat difficult to really study,” Hamden added. “But this work provides evidence that it was recently ejecting quite a lot of energy into space in the form of a jet and conical outflow.”
Learning More About the Milky Way
The researchers found the structures by analyzing images produced by the South African Radio Astronomy Observatory’s MeerKAT telescope, which has 64 satellite dishes that are each 65 feet (nearly 20 meters) tall and connected across 5 miles (about 8 kilometers) of a sparsely populated area with minimal interference.
“The new MeerKAT observations have been a game changer,” Yusef-Zadeh said. “It’s really a technical achievement from radio astronomers.”
Despite the similarities between the newly discovered filaments and those identified in 1984, the authors of the new study don’t think the populations share exactly the same traits.
The vertical filaments are located perpendicular to the galactic plane, while the horizontal ones are parallel to the plane and point radially toward the black hole, according to the news release. The vertical filaments surround the nucleus of the Milky Way, but the horizontal ones appear to spread out to one side toward the black hole.
“The distribution and alignment of the filaments can help show how the material has moved and distorted in the past,” Hamden said.
Their behavior also differs: The horizontal filaments emit thermal radiation and material associated with molecular clouds partially or fully embedded in the outflow from the black hole, the authors wrote. Molecular clouds consist of gas, dust and stars. The vertical filaments, on the other hand, are magnetic and hold cosmic ray electrons moving nearly as fast as the speed of light.
The authors think further studying the newfound filaments could help them “learn more about the black hole’s spin and accretion disk orientation,” Yusef-Zadeh said.
A black hole’s accretion disk is the thin, hot structure resulting from material from a nearby star being pulled into a circle around the black hole.
Follow-up is also needed to determine whether the jet-driven outflow from the black hole, and therefore more filaments, appear on both sides of the black hole, Hamden said. A jet in this context is a beam of matter ejected from some astronomical objects.
A black hole “typically ejects jets symmetrically … so there should be a pair,” Hamden added. “One way to confirm that the [filament] structure is created by something like a jet is to find both sides of it.”
This would add “to the complex, active picture of our own Milky Way,” she said.
Yusef-Zadeh said he believes their work is “never complete.”
“We always need to make new observations,” he said, “and continually challenge our ideas and tighten up our analysis.”
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