(ORDO NEWS) — Northwestern University astrophysicist Farhad Zadeh has been fascinated and puzzled by the family of large-scale, highly organized magnetic filaments dangling from the center of the Milky Way since he first discovered them in the early 1980s.
40 years later, Zadeh remains just as fascinated, but slightly less puzzled.
With the new discovery of similar filaments located in other galaxies, Zadeh and his collaborators presented for the first time two possible explanations for the unknown origin of the filaments.
Zadeh and his co-authors speculate that the filaments could result from interactions between large-scale wind and clouds, or could arise from turbulence within a weak magnetic field.
“We know a lot about the filaments in our galactic center, and now the filaments in the outer galaxies are starting to show up as a new population of extragalactic filaments,” Zadeh said.
“The underlying physical mechanisms for both populations of filaments are similar despite completely different environments.
The objects are part of the same family, but the filaments outside of the Milky Way are older, more distant cousins very distant (in time and space) cousins.”
“Something universal is happening”
The first filaments discovered by Zadeh stretched 150 light-years long and towered near the Milky Way’s central supermassive black hole.
Earlier this year, Zadeh added almost 1,000 more strands to his collection of observations. In this package, one-dimensional threads appear in pairs and groups, often stacked at equal distances from each other, like the strings on a harp, or spread out to the sides, like separate streams in a waterfall.
Using observations from radio telescopes, Zadeh discovered mysterious filaments consisting of cosmic ray electrons rotating along a magnetic field at a speed close to the speed of light.
Although he was putting together a puzzle about what the threads were made of, Zadeh still wondered where they came from.
When astronomers discovered a new population outside of our galaxy, it opened up new possibilities for studying the physical processes in the space surrounding the filaments.
The newly discovered filaments are inside a galaxy cluster, a concentrated tangle of thousands of galaxies located one billion light-years from Earth.
Some of the galaxies in the cluster are active radio galaxies that have become a breeding ground for the formation of large-scale magnetic filaments. When Zadeh first saw the newly discovered threads, he was amazed.
“After studying the filaments at our galactic center for all these years, I was very excited to see these incredibly beautiful structures,” he said. “Because we found these filaments elsewhere in the universe, this hints that something universal is going on.”
While the new population of filaments is similar to those found in the Milky Way, there are some key differences. The filaments outside the Milky Way are much larger, 100 to 10,000 times longer. They are also much older and their magnetic fields are weaker.
Curiously, most of them dangle – at 90-degree angles – from the jets of the black hole into the vast nothingness of the intra-cluster medium, or the space sandwiched between the galaxies within the cluster.
But the newly discovered population has the same length-to-width ratio as the Milky Way’s filaments. And both populations transfer energy using the same mechanisms.
Closer to the jets, the filament electrons are more energetic, but lose energy as they move down the filament.
While the black hole’s jet could provide the seed particles needed to create the filament, something unknown must be accelerating those particles to startling distances.
“Some of them are astoundingly long, up to 200 kiloparsecs,” Zadeh said. “That’s about four or five times the size of the entire Milky Way.
Remarkably, their electrons stay together over such a long distance. If an electron were to travel at the speed of light along the length of the filament, it would take 700,000 years for it to travel. And they don’t travel at the speed of light.”
In a new paper, Zadeh and his collaborators suggest that the origin of the filaments could be a simple interaction between the galactic wind and an obstacle such as a cloud. When the wind wraps around an obstacle, it creates a comet tail behind it.
“The wind comes from the movement of the galaxy itself as it rotates,” Zadeh explained. “It’s like sticking your hand out the window of a moving car. There is no wind outside, but you can feel the air moving. It sweeps the material and creates a filamentous structure.”
Simulation offers another real possibility. When the researchers modeled an active turbulent environment, long filamentous structures materialized. As the radio galaxies move, Zadeh explained, gravity can act on the medium and mix it up.
Then the medium forms patches of swirling vortices. After the weak magnetic field wraps around the vortices, it can stretch, coil and intensify, eventually turning into elongated filaments with a strong magnetic field.
While many questions remain, Zadeh remains delighted with the new discoveries.
“All these filaments outside of our galaxy are very old,” he said. “They are from almost a different era in our universe, and yet signal to the inhabitants of the Milky Way that there is a common origin for the formation of filaments. I think it’s wonderful.”
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