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A new study led by researchers from the Yunnan Observatories of the Chinese Academy of Sciences has unveiled a novel mechanism for filament splitting and the formation of double-decker filaments. Their findings were in The Astrophysical Journal Letters.

Previous studies have suggested that in some filament eruption mechanisms, such as magnetic reconnection, a filament will split if the reconnection occurs within it. In these cases, the split filament forms a transient double-decker configuration during its rise and eruption, which is an important mechanism for double-decker filament formation. This process requires a close temporal alignment between the filament's splitting and its eruption features.

In contrast to previously observed events, the team's analysis of joint multi-platform observational data from the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) and the Extreme Ultraviolet Imager (EUVI) of the Solar Terrestrial Relations Observatory (STEREO) reveals, for the first time, a filament splitting event caused by the component reconnection mechanism.

The splitting of the filament began more than an hour before any eruption features appeared. This finding indicates that, unlike in many past observations, the filament splitting was not triggered by the same physical process that led to the filament eruption.

During this unique splitting process, numerous small vertical jets emerged within the filament. These jets exhibited dynamic characteristics similar to the nanojets recently discovered in coronal loops, which arise from component reconnection between magnetic field lines with a small angle of misalignment.

This suggests that component reconnection can occur inside a braided filament flux rope, causing the multiple clusters of magnetic field lines constituting the filament to become more parallel after reconnection, ultimately leading to the splitting of the flux rope.

Notably, the study directly observed brightening filament threads with small-angle misalignments and the subsequent vertical small jets. This provides direct observational evidence for the component reconnection mechanism within the filament.

This study establishes a link between the small-scale component reconnection mechanism and the large-scale splitting of filaments, as well as the formation of double-decker filaments.

These findings not only illustrate the potential of the component reconnection mechanism to influence large-scale coronal magnetic structures and thermodynamic characteristics, but also offer new evidence of its prevalence—and that of its associated microflares.