Astronomers have discovered hundreds of strange thread-like structures that extend for several light years near the supermassive black hole at the center of our galaxy, the Milky Way, reports a new study.
While the origin of these filaments remains unclear, scientists think that they may be sculpted from a hidden outflow of gassy material emanating from our galaxy’s black hole, which is called Sagittarius A* (Sgr A*). The results shed new light on the strange environment around Sgr A*, which is located about 25,000 light years from Earth in a much denser and more turbulent part of the galaxy.
Supermassive black holes are the gravitational glue that holds galaxies together for billions of years, but these hyper-dense objects also cause bouts of tumult and chaos for anything in their vicinity. When black holes devour stars and gas clouds, they often erupt in pyrotechnic explosions that create bizarre structures and formations, such as jets, bubbles, or filaments.
Now, researchers led by Farhad Zadeh, a professor of physics and astronomy at Northwestern University, have discovered a new population of filaments, with lengths between five and ten light years, that radiate horizontally from Sgr A*, meaning that they are parallel to the galactic disk, or plane.
The team spotted the features while examining huge mosaic surveys of the galactic center that were captured by the sensitive MeerKAT radio telescope, located in South Africa. Future surveys “could potentially provide additional insight into the origin of the enigmatic galactic center filaments,” according to a study published on Friday in The Astrophysical Journal Letters.
“It was a total surprise discovery,” Zadeh told Motherboard in a call. “When you're doing such a large-scale survey, you just really don't know what you're going to find. That is especially true for MeerKAT’s mosaic image of the galactic center because there was no other good mosaic image of this region.”
“It’s a large region that is very rich in structures and we're basically studying them one at a time,” he added. “The latest discovery is finding this new population of filaments.”
Zadeh has been enchanted by the center of the Milky Way for decades, and has identified many structures and phenomena that exist in this region over the course of his career. In the 1980s, he and his colleagues discovered huge “vertical” filaments—meaning that the structures are perpendicular to the Milky Way’s disk—that reach lengths of 150 light years, and which still remain unexplained.
“This is a very rich region of the galaxy, and some people call it confusing and don’t want to touch it. Some people, like me, who are fool enough, spend a lot of time trying to figure it out,” Zadeh said. “I love the idea of just getting into really messy things in the hope of finding some order. That’s usually satisfying.”
To that end, Zadeh and his colleagues were exploring MeerKAT’s sweeping surveys in part to better understand the origin and nature of the mysterious vertical filaments. That’s how they ended up spotting the new population of shorter filaments, which appear to radiate out from Sgr A* horizontally like the spokes of the bicycle wheel.
These structures differ from their vertical counterparts in many ways beyond their alignment to the galactic plane. The vertical structures are shaped by clear magnetic fields, and they shoot particles traveling close to the speed of light all around the galactic core. The horizontal filaments glow in lower-energy thermal radiation and only fan out along one side of Sgr A*. Moreover, the horizontal structures are much shorter and less abundant than the vertical filaments, suggesting that the two populations were made by different processes.
Fortunately, the horizontal filaments offer a few more clues about their origin than the vertical structures, especially given that they are only positioned along one edge of Sgr A*. This hints that the filaments may be sculpted by a hidden outflow of gassy material that the supermassive black hole is pushing into the galactic plane.
Such outflows are commonly observed in other galaxies, fueled by intense interactions between supermassive black holes and the material that is unlucky enough to fall into them. Sometimes, a black hole receives such a huge gulp of gas that it belches out radiant jets of energy and light, which typically shoot from its poles at a perpendicular angle to the galactic plane.
Previous studies have suggested that Sgr A*, which is relatively starved of gas at the moment, is emitting a much weaker jet into the Milky Way at an unusual angle that is more parallel to the galactic plane. Zadeh and his colleagues think that the newly discovered horizontal filaments may be forged by the dim outflow of this jet, which the team said would have peaked in intensity about six million years ago.
It will take more observations to probe this possible origin for the horizontal filaments, but If it were to be confirmed, the results could reveal new insights about Sgr A*, such as its spin and past activity.
For now, however, the discovery serves as another reminder that many dynamic and mysterious phenomena remain hidden in the dense central plane of our galaxy.
“You have to really look at the [galactic] plane even though it's messy,” Zadeh said. “You never know what you're going to uncover.”