(ORDO NEWS) — We are getting close to unraveling a strange mystery represented by hundreds of huge filaments dangling through the heart of the Milky Way.
For the first time, these long magnetized filaments, glowing in radio waves, have been observed coming out of other galaxies.
Not only are they no longer unique to the Milky Way, the range of environments in which they can be found allows scientists to narrow down the mechanisms that create them.
Astrophysicist Farhad Yusuf-Zadeh of Northwestern University in the US first discovered the Milky Way’s filaments in the 1980s and has been puzzling over them ever since.
According to Yusuf-Zade, there are two possible explanations. The first is the interaction between galactic winds and large clouds; the second is turbulence in weak magnetic fields caused by the movement of galaxies.
“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 new populations of extragalactic filaments,” says Yusuf-Zade.
“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 the Milky Way are older, more distant relatives and I mean very distant (in time and space) relatives.”
About 1,000 filaments up to 150 light-years long and dangling in a surprisingly neat and ordered arrangement like harp strings have been detected in the Milky Way to date, most recently by the MeerKAT radio telescope in South Africa.
Precise telescope observations of the galactic center – penetrating thick dust and gas that obscures much of what s is inside – have increased the number of previously known filaments by a factor of ten.
These radio observations also showed that the filaments contained cosmic ray electrons spinning in magnetic fields at close to the speed of light, and that the magnetic fields were amplified along the entire length of all filaments.
Without more information, it would be difficult to figure out why they are there, just hovering quietly in the galactic center.
The discovery of additional filaments in four different clusters of galaxies, ranging from 163 million to 652 million light years away, is a huge breakthrough.
“After studying fibers at our own Galactic Center for all these years, I was very excited to see these incredibly beautiful structures,” says Yusuf-Zade. “Because we found these filaments elsewhere in the universe, this hints that something universal is going on.”
The newly discovered filaments outside the Milky Way differ from the filamentary structures of our galaxy in several rather important ways.
They are associated with jets and lobes of radio galaxies – huge structures that erupt from the galactic center and extend for vast distances on both sides of the galactic plane.
The filaments emanating from these jets and lobes are also much larger than the structures seen at the center of the Milky Way, from 100 to 1000 times larger.
“Some of them are astonishingly long, up to 200 kiloparsecs,” says Yusuf-Zadeh.
“That’s about four or five times the size of our entire Milky Way. 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. And they don’t travel at the speed of light.”
Filaments extending approximately at right angles from the jet of the radio galaxy. (Radnik and others)
They are also older and their magnetic fields are weaker.
And, of course, they extend into intergalactic space, often at right angles to the jets. The filaments of the Milky Way appear to be centered on the galactic disk.
On the other hand, the similarity is strong. Galactic and extragalactic filaments have the same ratio of length to width, and the mechanism of cosmic ray transfer is the same. If the same mechanism produces all the filaments, it must work at different scales.
Winds may be one such mechanism. Active supermassive black holes and violent star formation can generate galactic winds rushing into intergalactic space.
These winds can push thin clouds of gas and dust that drift through interstellar and intergalactic space, pushing material together to create filamentous structures.
Simulations suggested another possibility: turbulence in the medium caused by gravitational perturbations.
This turbulence can create whirlpools in the intergalactic medium around which weak magnetic fields get hooked, twisted and eventually pulled into filaments with strong magnetic fields.
This is not a definitive answer – yet. We don’t even know for sure whether the same mechanism is responsible for both types of filaments, or whether completely different phenomena create structures that look uncannyly similar.
“All these filaments outside of our galaxy are very old. ”, says Yusuf-Zade.
“They are almost from 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 remarkable. ”
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