In the absolute omnishambles of the Milky Way galactic center, we’ve just found a new kind of turbulent structure.
Peering into the Central Molecular Zone (CMZ) that surrounds the galactic supermassive black hole, astronomers have identified long, thin filaments of gas, near outflows of material. Filaments have been identified around the galactic center previously, but these new ones are unlike any other filaments ever seen.
After puzzlement, then analysis, a team of astronomers led by Kai Yang of Shanghai Jiao Tong University has determined that they represent a never-before-seen mechanism for the dispersal of gas throughout the CMZ – a kind of cosmic tornado.
“When we checked the ALMA images showing the outflows, we noticed these long and narrow filaments spatially offset from any star-forming regions,” Yang says. “Unlike any objects we know, these filaments really surprised us.”
The CMZ is a region of clouds rich in dust and molecular gas that roils around the galactic nucleus. It measures up to 2,000 light-years across, and it’s dense. It contains nearly 80 percent of all the dense gas in the galaxy, and around 5 percent of all the galaxy’s molecular gas.
As you can imagine, all this densely packed material makes for a bit of a wild environment, with clouds slamming through space at up to 100 kilometers per second. Shock fronts and turbulence are common. Clouds form, break apart, and reform in an endless cycle.
It’s not clear what drives this process, but the CMZ is kind of hard to study. Because the clouds therein are so dense, it can be a little tricky to peer into their midst. Yang and colleagues used the powerful Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to try to shed some light on the dynamic processes at play in the CMZ.
They were specifically looking for traces of silicon monoxide, a gas whose presence is particularly useful in tracing and delineating shocks. They weren’t expecting what they found, though: very long, narrow filaments traced out in silicon monoxide at a finer scale than other filaments found in the CMZ.
The research team named these structures “slim filaments,” and set about analyzing them in greater detail. In addition to silicon monoxide, the slim filaments contain the complex organic molecules cyclopropenylidene, formaldehyde, cyanoacetylene, methanol, isocyanic acid, sulfur monoxide, and acetonitrile.
In addition, their velocity distributions are inconsistent with measurements of other kinds of filaments, and they are dominated by turbulent pressure. This suggests that the structures may be a little bit like tornadoes, or dust devils, and perform a similar role.
“Our research contributes to the fascinating Galactic Center landscape by uncovering these slim filaments as an important part of material circulation,” says astronomer Xing Lu of Shanghai Astronomical Observatory in China.
“We can envision these as space tornadoes: they are violent streams of gas, they dissipate shortly, and they distribute materials into the environment efficiently.”
Although how the slim filaments form is unclear, the researchers believe that shock plays a role in their genesis. Shocks generated by collisions in the CMZ may give rise to filaments of turbulence that heat complex molecules into their gas phase and release them into the interstellar medium.
As they cool, these molecules revert to dust, replenishing the CMZ and redistributing its material. If the filaments are as abundant throughout the CMZ as the researchers found them in their observation sample, they would explain a large part of the recycling rate of the region.
“We speculate that these slim filaments represent a distinct class from the dense gas filaments typically observed in nearby molecular clouds, and they may result from interactions between shocks and molecular clouds,” the researchers write in their paper.
“Their eventual dissipation within 10,000 years may enrich silicon monoxide and several complex organic molecules in the interstellar medium, thus leading to the observed widespread emission of silicon monoxide and complex organic molecules in the CMZ.”
The research has been published in Astronomy & Astrophysics.
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