Led by the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences, researchers studied G165, a massive cloud of atomic hydrogen moving at approximately 300 kilometers per second. Located around 50,000 light-years from Earth and situated far above the galactic plane, G165 provides a pristine observational window into early cloud formation.
Unlike high-velocity clouds (HVCs) that often contain a mixture of warm and cold gas, G165 is composed almost entirely of warm neutral medium (WNM), with negligible cold components. This composition, verified through FAST observations, positions VHVCs like G165 as potential precursors to more evolved interstellar structures.
FAST's high-resolution HI 21 cm data revealed that G165's gas is highly structured and supersonic, contradicting earlier assumptions that WNM in remote regions is smooth and quiescent. Instead, a dense lattice of velocity-coherent filaments spans the cloud, forming complex three-dimensional patterns with visible signs of turbulent motion.
To better understand the origin of these features, the team used magnetohydrodynamic simulations. These models showed that supersonic turbulence combined with magnetic fields can account for the observed characteristics, including velocity layering, asymmetrical profiles, and skewed density distributions. Crucially, these effects appear without the influence of gravity, highlighting the powerful role of turbulence and magnetism in shaping cosmic gas.
This finding not only provides a clearer picture of interstellar cloud dynamics but also suggests how atomic gas in remote galactic environments might evolve toward star formation. The identification of supersonic filamentary structures in a WNM-dominated VHVC could mark a new chapter in understanding how structure arises in low-gravity regions of space.
Research Report:A network of velocity-coherent filaments formed by supersonic turbulence in a very-high-velocity H i cloud
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