Deep in the heart of our galaxy, far beyond the serene skies we gaze upon, lies a region of untamed cosmic fury—the Central Molecular Zone (CMZ). This vast, turbulent expanse surrounds Sagittarius A (Sgr A*), the supermassive black hole anchoring the Milky Way. Here, clouds of gas and dust twist, collide, and churn as powerful shock waves ripple outward in all directions. For decades, astronomers have known that this galactic heartland is in constant, chaotic motion, yet its underlying processes have remained elusive. That is, until now.
With the unparalleled eyes of the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of astronomers has zoomed in on this mysterious region with unprecedented clarity. What they discovered has added a thrilling new chapter to our understanding of the galaxy’s beating heart: the existence of previously unseen, slim filamentary structures, unlike anything observed before.
These newly discovered “slim filaments”—long, narrow threads of molecular gas—offer fresh insight into how materials cycle through destruction and rebirth in the galaxy’s core. Their discovery sharpens our view of the Milky Way’s most enigmatic zone by a staggering factor of 100 and opens an intriguing window into a previously hidden layer of galactic dynamics.
The Central Molecular Zone: A Cosmic Cauldron
The CMZ is not your average stellar nursery. Spanning the innermost 500 light-years of the Milky Way, it is a place where conditions are extreme—densities are higher, temperatures are hotter, and the interstellar medium is in a perpetual state of flux. Molecular clouds, thick with dust and gases like carbon monoxide and ammonia, swirl under the gravitational influence of Sgr A* and interact with violent outflows from young, massive stars and supernova explosions.
Despite its chaos, the CMZ is a cradle of star formation, responsible for birthing stars at rates far higher than the galactic average. Yet, much about its processes remains a puzzle. How does gas collapse into stars in such a hostile environment? What drives the endless cycling of dust and molecules through formation, destruction, and reformation? These questions have long confounded scientists.
A Serendipitous Discovery: Slim Filaments
Enter ALMA. Perched high in the Chilean Andes, this world-class radio observatory excels at peering through dense clouds of dust to reveal the hidden workings of the cosmos. Using ALMA’s remarkable sensitivity and resolution, researchers led by Kai Yang of Shanghai Jiao Tong University homed in on molecular tracers within the CMZ—specifically focusing on silicon monoxide (SiO).
SiO is a well-known marker of shock waves. When interstellar shocks plow through molecular clouds, they liberate silicon atoms from dust grains. These atoms quickly combine with oxygen to form SiO, which can then be detected via its spectral fingerprints. By mapping the emission of SiO’s rotational transition—especially the SiO 5-4 line—the team hoped to unravel the shock dynamics at play near the Milky Way’s center.
But something unexpected appeared in the data. Instead of finding just turbulent clouds or outflows tied to star formation, they identified slim, thread-like structures extending across the chaotic landscape. These filaments didn’t correspond to any known star-forming regions, nor did they behave like typical molecular outflows. Their presence was entirely unforeseen.
“When we checked the ALMA images showing the outflows, we noticed these long and narrow filaments spatially offset from any star-forming regions,” Yang recalls. “Unlike any objects we know, these filaments really surprised us. Since then, we have been pondering what they are.”
Space Tornadoes: Violent, Fleeting, and Fundamental
What exactly are these structures? According to Xing Lu, research professor at the Shanghai Astronomical Observatory and a corresponding author on the study, these filaments can be envisioned as “space tornadoes.”
“They are violent streams of gas, they dissipate quickly, and they distribute materials into the environment efficiently,” Lu explains.
Unlike more stable, well-behaved filaments elsewhere in the galaxy—structures often associated with the slow, steady birth of stars—these slim filaments are dynamic and ephemeral. Their line-of-sight velocities are coherent but inconsistent with known outflows or gravitationally bound structures. Moreover, they show no significant dust emission, implying they are not enshrouded by dense, cold dust like most star-forming filaments. This rules out the possibility that they are simply unnoticed sites of stellar birth.
What the team did detect was something much more dynamic. The filaments appear to be shock-driven features that help cycle materials between different phases within the CMZ. ALMA’s observations revealed molecular fingerprints from not just SiO, but also methanol (CH₃OH) masers and complex organic molecules like methyl cyanide (CH₃CN) and cyanoacetylene (HC₃N). These molecules typically emerge from high-energy processes—further pointing toward shocks as the driving mechanism.
How Slim Filaments Fit Into the Galactic Puzzle
The existence of these slim filaments sheds light on an important, previously hidden aspect of how material circulates in the CMZ. According to the researchers, the process works like this:
- Shock Waves Strike: Powerful shocks ripple through molecular clouds, often triggered by dynamic interactions in the CMZ such as stellar winds, supernova blasts, or gravitational forces near Sgr A*.
- Formation of Slim Filaments: These shocks compress and funnel gas into narrow, thread-like filaments. Within them, molecules like SiO, CH₃OH, and others are released from dust grains and injected into the interstellar medium.
- Filaments Dissipate: These structures are transient. They eventually dissipate, releasing their material back into the surrounding environment.
- Material Cycles Onward: Once free-floating, the molecules either freeze back onto dust grains or become incorporated into new structures, maintaining a balance of depletion and replenishment in the CMZ.
If slim filaments are as widespread as this study suggests, they may be a crucial mechanism in this cycle—helping to distribute material efficiently and sustain the dynamic equilibrium of the galactic core.
ALMA’s Role in Cracking the Code
None of this would have been possible without ALMA’s cutting-edge technology. Its array of 66 high-precision antennas, spread across the Atacama Desert, provided the fine angular resolution needed to isolate these delicate structures. The team was able to resolve details on scales as small as 0.01 parsecs—about 2,000 astronomical units, or roughly 50 times the distance between the Sun and Pluto.
“ALMA’s high angular resolution and extraordinary sensitivity were essential to detect these molecular line emissions associated with the slim filaments, and to confirm that there is no association between these structures with dust emissions,” emphasizes Yichen Zhang, another corresponding author from Shanghai Jiao Tong University.
Their study, published in Astronomy & Astrophysics, marks a significant leap forward in our ability to map the dynamic processes at the heart of the Milky Way.
What’s Next? Hunting for the Origins
While the discovery is groundbreaking, it also opens up new questions. Chief among them: how exactly do these filaments form? What kinds of shocks generate them, and under what conditions? Are they primarily driven by stellar feedback, gravitational instabilities, or some combination of factors unique to the galactic center?
Future ALMA campaigns aim to address these mysteries. By observing multiple SiO transitions and conducting a comprehensive census of slim filaments across the CMZ, astronomers hope to confirm whether these structures are common and to model the full life cycle of molecular gas in the region.
The team also plans to integrate numerical simulations into their analysis. By comparing real observations to computer models of shock-induced dynamics, researchers can test different scenarios for filament formation and evolution. These studies will not only enhance our understanding of the Milky Way but also provide insight into similar galactic centers in distant galaxies.
A Glimpse Into Our Galaxy’s Beating Heart
The discovery of slim filaments is a reminder that even in our own galactic backyard, there’s still so much to uncover. The CMZ remains one of the most extreme and mysterious environments in the Milky Way. Yet thanks to cutting-edge observatories like ALMA and the tenacious curiosity of astronomers, we are inching closer to understanding its complex, chaotic nature.
As Kai Yang and his team continue their quest, the story of the Milky Way’s core is being rewritten—one slender filament at a time.
Reference: Kai Yang et al, ALMA observations of massive clouds in the central molecular zone: slim filaments tracing parsec-scale shocks, Astronomy & Astrophysics (2025). DOI: 10.1051/0004-6361/202453191