Solar sympathetic filament eruptions usually involve two or more filament eruptions that occur simultaneously or successively within a relatively short time interval with a certain causal linkage. The eruption of one filament may have an effect on another one, thus resulting in the eruption of the other filament simultaneously or successively.

Researchers led by Dr. YANG Liping and Prof. YAN Xiaoli from the Yunnan Observatories of the Chinese Academy of Sciences have studied the interaction process between two nearby filaments in the active region NOAA 12866 on September 9, 2021, using data from the 1-m New Vacuum Solar Telescope (NVST) and the Solar Dynamic Observatory (SDO).

The study was published in The Astrophysical Journal on Jan. 25.

They found that the right part of the larger filament became active first and erupted after appearance of the brightening and bidirectional flows between the larger filament and a near smaller filament. During its eruption process, it continuously approached the smaller filament. Then they collided with each other, and the interaction happened between them. In the following, the brightening and bidirectional flows appeared between them.

"This implies that magnetic reconnection occurred between the threads of two filaments," said Dr. YANG. The interaction resulted in a rightward motion of the smaller filament at first, and then its activation, and finally a part of it erupted. When the erupted smaller filament deflected rapidly toward the middle part of the larger filament, the left part of the larger filament erupted with its overlying magnetic fields disturbed by the smaller filament.

Furthermore, the researchers found that the two filaments had opposite signs of helicity, and when they collided with each other at a smaller contact angle of less than 45°, the magnetic reconnection between them would happen.

"These successive eruptions occurred in a relatively short time with a certain causal linkage, and their eruptions were caused by filament interaction, which can be called sympathetic eruptions," said Prof. YAN.

This study provides new clues for understanding solar sympathetic eruptions and for studying the continuous explosions of stars or other celestial bodies.