Earlier this year, astronomers announced the discovery of almost 1,000 magnetic filaments surrounding the core of our galaxy, the Milky Way. Some of these structures have been known for four decades but scientists couldn’t find a satisfactory explanation for them – the discovery of so many more provided more insights but no solution. Now, astronomers have found similar structures further afield and think there are two possible explanations.
Magnetic fields are not that puzzling in space – they are actually pretty common. However, these magnetic filaments are truly weird. The way to detect them is via radio waves, but if they were visible to regular telescopes, they would look like the lens was covered in hair.
Casting telescopes further afield, the team discovered that filaments also existed around a galaxy cluster one billion light-years away from us. This region is home to thousands of galaxies, including several active radio galaxies. These appear to be the perfect breeding ground for magnetic filaments that are both much larger and much older than those seen around the center of the Milky Way.
"We know a lot about the filaments in our own Galactic Center, and now filaments in outside galaxies are beginning to show up as a new population of extragalactic filaments," Farhad Yusef-Zadeh, from Northwestern University, said in a statement. "The underlying physical mechanisms for both populations of filaments are similar despite the vastly different environments. The objects are part of the same family, but the filaments outside the Milky Way are older, distant cousins—and I mean very distant (in time and space) cousins."
The location in the Milky Way and elsewhere suggests a connection with supermassive black holes, located at the center of galaxies, and the jets of material they release once they undergo a feeding frenzy.
In the Milky Way, the filaments are about 150 light-years long, towering near our supermassive black hole Sagittarius A* – but in the galaxy cluster, they are 100 to 10,000 longer, with some reaching 700,000 light-years. That’s four to five times bigger than the whole Milky Way. It would have taken electrically charged particles a very long time to create.
"After studying filaments in our own Galactic Center for all these years, I was extremely excited to see these tremendously beautiful structures," Zadeh said. "Because we found these filaments elsewhere in the universe, it hints that something universal is happening.”
The extragalactic filaments appear to exist at about 90 degrees with respect to the direction of the black hole jet, a peculiarity not seen in the Milky Way. However, they have the same length-to-width ratio as our local filaments and they carry energy with the same mechanisms.
One explanation is that the galactic wind of electrically charged particles generated by a galaxy rotating interacts with an unexpected structure like a gas cloud. This creates an object with a comet-like tail behind it: a good fit for the magnetic filaments. The other explanation comes from simulations, where a turbulent medium creates swirls with a weak magnetic field, and from that, a filamentary structure arises.
More observations will be required to understand exactly what’s going on, but the existence of these structures so far in space and time is remarkable
"All of these filaments outside our galaxy are very old," Zadeh added. "They are almost from a different era of our universe and yet signaling the Milky Way inhabitants that a common origin exists for the formation of the filaments. I think this is remarkable."
The work is published in The Astrophysical Journal Letters.