The new image from the MeerKAT telescope at the South African Radio Astronomy Observatory (SARAO) in Cape Town, South Africa, shows nearly 1,000 magnetized threads in the Galactic center.
The radio-emitting filaments are one-dimensional magnetic structures up to 150 light-years long.
They are found in pairs and clusters, often stacked equally spaced, side by side like strings on a harp.
They were first discovered in the early 1980s by a team of astronomers led by Northwestern University’s Professor Farhad Yusef-Zadeh.
“Those observations showed linear, magnetized features running mainly perpendicular to the Galactic plane,” Professor Yusef-Zadeh and his colleagues explained.
“Their morphology was unique and different than shell-like or jet-like nonthermal radio continuum sources that had been observed.”
“This was the first indication that the nucleus of our Galaxy harbors energetic activity that produces relativistic particles along straight filaments with no obvious source of acceleration.”
The new MeerKAT image shows 10 times more such filaments than previously discovered, enabling the astronomers to conduct statistical studies across a broad population of filaments for the first time.
“We have studied individual filaments for a long time with a myopic view,” Professor Yusef-Zadeh said.
“Now, we finally see the big picture — a panoramic view filled with an abundance of filaments. Just examining a few filaments makes it difficult to draw any real conclusion about what they are and where they came from. This is a watershed in furthering our understanding of these structures.”
In their study, the researchers explored the filaments’ magnetic fields and the role of cosmic rays in illuminating these fields.
They found that the filaments are likely related to past activity of the Milky Way’s supermassive black hole rather than coordinated bursts of supernovae.
The filaments also could be related to enormous, radio-emitting bubbles, which the team discovered in 2019.
And, while they already knew the filaments are magnetized, now they can say magnetic fields are amplified along the filaments, a primary characteristic all the filaments share.
“This is the first time we have been able to study statistical characteristics of the filaments. By studying the statistics, we can learn more about the properties of these unusual sources,” Professor Yusef-Zade said.
Among the remaining mysteries, the authors are particularly puzzled by how structured the filaments appear.
Filaments within clusters are separated from one another at perfectly equal distances — about the distance from Earth to the Sun.
“They almost resemble the regular spacing in solar loops. We still don’t know why they come in clusters or understand how they separate, and we don’t know how these regular spacings happen. Every time we answer one question, multiple other questions arise,” Professor Yusef-Zade.
The scientists also still don’t know whether the filaments move or change over time or what is causing the electrons to accelerate at such incredible speeds.
“How do you accelerate electrons at close to the speed of light? One idea is there are some sources at the end of these filaments that are accelerating these particles,” Professor Yusef-Zade said.
The team’s paper appears in the Astrophysical Journal Letters.
F. Yusef-Zadeh et al. 2022. Statistical Properties of the Population of the Galactic Center Filaments: the Spectral Index and Equipartition Magnetic Field. ApJL 925, L18; doi: 10.3847/2041-8213/ac4802
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