Astronomers have discovered distant relatives of the huge, highly organized magnetic filaments dangling from the center of the Milky Way, and this discovery could help scientists finally explain these mysterious structures.
These filaments hang around the supermassive black hole at the center of the Milky Way. Astrophysicist Farhad Zadeh, now at Northwestern University in Illinois, first discovered these structures in the 1980s, when they puzzled and fascinated him. But earlier this year, Zadeh discovered about 1,000 such filaments in a distant galaxy, providing a new clue. These magnetic threads appear in pairs or groups, sometimes even folded and spaced at the same distance from each other. Comparing the distant filaments with their previous discovery, Zadeh and his colleagues proposed two possible explanations for their origin: interaction between large-scale wind and clouds, or turbulence within a weak magnetic field.
“We know a lot about the filaments in our own galactic center, and now the filaments in the outer galaxies are starting to emerge as a new population of extragalactic filaments,” Zadeh said in a statement. “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 — and I mean very distant and cosmic cousins.”
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Ever since Zadeh first discovered the filaments of the Milky Way, he has used radio telescopes to determine that these elements are made up of electrons trapped in magnetic fields and vibrating at nearly the speed of light.
But understanding how these filaments formed required the study of a new population of filaments located in a concentrated cluster of thousands of galaxies 1 billion light-years from Earth. Particularly intriguing was that some of these galaxies are active radio galaxies that appear to be forming large-scale magnetic filaments.
“After studying the filaments at our own galactic center for all these years, I was very excited to see these incredibly beautiful structures,” Zadeh said in a statement. “Because we found these filaments elsewhere in the universe, this hints that something universal is going on.”
Filaments with a family resemblance
The newly discovered population of extragalactic filaments resembles those found around the black hole at the center of our galaxy, but has some key differences.
In particular, the filaments in this cluster of galaxies are much larger than those in the Milky Way, 100 to 10,000 times longer. Some of these extragalactic filaments are up to 200 parsecs long, which is about 650,000 light years. However, despite their larger size, the filaments in a cluster of galaxies have the same length-to-width ratio as the Milky Way’s filaments, and both sets of filaments appear to carry energy in the same way.
The filaments in a cluster of galaxies hang from jets of black holes.
Closer to the black hole jet, the electrons in the filament are more energetic, losing energy as they move down the filament. This trend indicates that while black hole jets can accelerate electrons to the speed of light, providing particles to form these filaments, some other unknown process is ejecting particles along the incredible length of filaments.
“Some of them are astonishingly long, up to 200 kiloparsecs, which is about four or five times the size of our entire Milky Way,” Zadeh said. “What is remarkable is that 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. They don’t travel at the speed of light.”
The new population of extragalactic filaments also appears to be much older and with weaker magnetic fields than their Milky Way cousins.
Zadeh and colleagues speculate that the filaments could be the result of a simple interaction between obstructions such as clouds of gas or dust and galactic winds, which are high-speed stellar winds from newly formed massive stars or from supermassive black holes. . As these winds wrap around these clouds of gas and dust, they create a comet-like tail.
“The wind comes from the motion of the galaxy itself as it rotates,” Zadeh said. “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. loose. It sweeps the material and creates a filamentous structure.”
However, when the team simulated the turbulent intracluster environment, long filamentous structures developed, pointing to an alternative creation mechanism. When radio galaxies move, their gravitational influences perturb this medium, creating plasma swirls. Weak magnetic fields then wrap around these vortices, stretching and amplifying the magnetic fields, eventually turning the fields into long filaments.
Even with two potential formation mechanisms, Zadeh is still fascinated by filaments.
“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.”
The team’s study was published Nov. 2 in the Astrophysical Journal Letters.
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