We are getting closer to solving the strange mysteries presented by the hundreds of giant threads hanging inside the Milky Way.
For the first time, long, magnetic streaks that radiate radio waves have been observed emanating from other galaxies. Not only are they no longer unique to the Milky Way, the different locations they can be found in allow scientists to narrow down the processes that make them.
Astronomer 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-Zadeh, there are two explanations. The first is the connection between storms and large clouds; the second is turbulence within the magnetic field induced by the motion of galaxies.
“We know a lot about the filaments in our Galactic Center, and now the filaments outside the galaxy are starting to show new populations of extragalactic filaments,” Yusuf-Zadeh says.
“The composition of all types of filaments is the same even though they are very different. The objects are part of the same family, but the filaments outside the Milky Way are a big, distant relative – and I mean it. very much distant (in time and space) cousins.”
About 1,000 of the filaments, which stretch up to 150 light-years and hang in a strange and orderly manner like harp strings, have been discovered in the Milky Way so far, most recently thanks to the MeerKAT radio telescope in South Africa.
The telescope’s powerful look at the galaxy’s center – into the dark dust and gas that hides much of the interior – increased the number of filaments already known by a factor of ten. These radio waves also revealed that the fiber contains cosmic ray electrons that spin in magnetic fields at near the speed of light, and that the magnetic field is amplified throughout the length of the fiber.
Without much knowledge, figuring out why they are there, just hanging out quietly among the galaxies, can be difficult. The discovery of extra galaxies, in four groups of different galaxies between 163 million and 652 million light-years away, is a great achievement.
“After studying filaments in our Galactic Center for all these years, I was very happy to see these beautiful buildings,” says Yusuf-Zadeh. “Because we’ve found these threads elsewhere in the Universe, it shows that there’s something in the universe going on.”
The newly discovered filaments outside the Milky Way are different from the filaments of our own galaxy in several important ways. They are associated with the jets and lobes of radio galaxies – large ones that erupt from the center of the galaxy, far apart on either side of the plane. The filaments emanating from these jets and lobes are also larger than those seen in the center of the Milky Way – between 100 and 1,000 times larger.
“Some of them have incredible lengths, up to 200 kiloparsecs,” says Yusuf-Zadeh.
“That’s four to five times the size of our entire Milky Way. What’s interesting is that their electrons stay together on such a long time scale. If an electron travels at the speed of light along the length of the filament, it can get caught up. 700,000 years. And they don’t move. at the speed of light.
They are also older, and their magnetic field strength is lower. And, of course, they continue through the air, often at right angles to the jets. The Milky Way galaxy appears to be in this galaxy.
On the other hand, the similarity is strong. Galactic and extragalactic galaxies have the same height-to-width ratio, and the cosmic ray path is the same. If the same machine is going to make all the threads, it should be something that works on different scales.
Wind can be one of those ways. Supermassive black holes and interstellar expansion can create storms that blow through space. These winds can push turbulent clouds of gas and dust through the atmosphere and between galaxies, which push the material together to form spiral galaxies.
The simulations also revealed another possibility: interstellar turbulence, caused by gravitational disturbances. This turbulence can create eddies within the intergalactic medium, in which weak magnetic fields are shaken, bent, and eventually stretched into filaments with strong magnetic fields.
It’s not a definitive answer – yet. We don’t even know if the same machine is responsible for all types of fibers, or if very different processes produce things that look the same.
“All these clouds outside our galaxy are very old,” says Yusuf-Zadeh.
“They’re almost from a different era of our Universe and yet they show the inhabitants of the Milky Way that a single origin exists to form the filament. I think that’s amazing.”
Research has been published in Astrophysical Journal Letters.