Astronomers have identified what they describe as "space tornadoes" raging near the center of the Milky Way, close to the galaxy’s supermassive black hole known as Sagittarius A* (Sgr A*). This discovery has allowed the researchers to gain a more comprehensive understanding of the ongoing cycle of material creation and destruction occurring at the core of our galaxy.
The discovery was made possible through observations using the Atacama Large Millimeter/submillimeter Array (ALMA), a powerful radio telescope network located in Chile. ALMA’s high-resolution capabilities enhanced our view of the motions within a region called the central molecular zone (CMZ) by a factor of 100, providing unprecedented detail.
Xing Lu, a member of the research team from the Shanghai Astronomical Observatory, explained that their work adds to the intriguing environment of the Galactic Center by uncovering these thin, filament-like structures as an essential part of how material circulates. He described these filaments as akin to space tornadoes: fast-moving, violent streams of gas that dissipate quickly but efficiently spread materials into the surrounding space.
The CMZ has long been known to be filled with swirling clouds of dust and molecules constantly undergoing cycles of formation and destruction. Despite this, the underlying mechanism driving these processes remained unclear.
Kai Yang, the study’s lead researcher from Shanghai Jiao Tong University, shared that when examining ALMA images showing outflows in the CMZ, the team noticed long, narrow filaments that were spatially distinct from any known star-forming regions. These filaments were unlike anything the researchers had previously encountered, which sparked their curiosity and led them to investigate further.
To analyze these filaments, the team used molecules as tracers to follow various physical and chemical processes occurring within the molecular clouds of the CMZ. Silicon monoxide (SiO) proved particularly useful for tracking energetic shockwaves rippling through the region.
ALMA detected new types of filamentary structures characterized by their long and slender shapes, observed through spectral lines of silicon monoxide and eight other molecules within the CMZ. These filaments were resolved at an extremely fine scale of about 0.033 light-years (0.01 parsecs)—remarkable, given that the CMZ itself is roughly 27,800 light-years from Earth.
These fine filaments differ significantly from other denser gas filaments previously seen in the CMZ. Notably, their velocities do not match typical outflows of matter, nor are they associated with dust emissions in the region. Additionally, the filaments do not appear to be in hydrostatic equilibrium—meaning the inward pull of gravity is not counterbalanced by the outward pressure from the gas and dust within the filaments.
Although astronomers do not yet know precisely how these thin filaments form, the observations hint strongly at shockwave-driven processes. Evidence supporting this includes changes in the energy levels of silicon monoxide molecules caused by rotational transitions, producing a specific emission known as SiO 5-4. The abundance of organic molecules detected in the filaments by ALMA also supports this theory.
The researchers propose that shocks initiate the formation of these thin filaments by releasing silicon monoxide and organic molecules such as methanol, methyl cyanide, and cyanoacetylene into the interstellar medium. After forming, the filaments eventually dissipate, which replenishes the shocked material in the CMZ.
Subsequently, these molecules freeze and form dust grains, establishing a balance between the depletion and replenishment of material in this dynamic environment.
Yichen Zhang, another team member from Shanghai Jiao Tong University, highlighted that ALMA’s exceptional angular resolution and sensitivity were crucial for detecting the molecular line emissions from these slim filaments. These observations confirmed the lack of dust emission association with the filaments. He emphasized that detecting these structures on a 0.01-parsec scale is a major step forward, revealing the working surface of the shocks within the CMZ.
If these fine filaments are widespread throughout the CMZ, as suggested by their presence in the ALMA sample region, this implies a balance in the cycle of molecular destruction and creation at the galaxy’s core.
Silicon monoxide is unique because it exclusively traces shock events, and its SiO 5-4 rotational transition emission is only detectable in shocked regions with relatively high density and temperature. This makes SiO a particularly valuable molecule for studying shock-induced processes in the dense environment of the CMZ.
The researchers hope future ALMA observations will extend beyond the SiO 5-4 transition to cover a broader area of the CMZ, which could further clarify the origins and roles of these slim filaments.
Combining these observations with simulations could ultimately confirm how the filaments form and evolve, providing deeper insight into the cyclical processes governing the extraordinary environment at the Milky Way’s heart.
This research was published in February in the journal Astronomy & Astrophysics.