A New Explanation on the Nature of Three-part Structure of CMEs

CMEs often exhibit the archetypical three-part structure in coronagraphs, including the bright core, dark cavity, and bright front. In the popular explanation, the bright core corresponds to the cold and dense filament, which locates at the dip of MFR. The dark cavity is the MFR with relatively lower density due to the enhanced magnetic pressure. The bright front originates from the pileup of background plasma along the MFR boundary. For many years, there has been no controversy over this traditional opinion. Based on a series of studies (Song et al. 2017, 2019a, 2019b, 2022, 2023a, 2023b, 2025a, 2025b), we completed a new explanation on the nature of the three-part structure of CMEs. The new explanation suggests that the MFR is responsible for the bright core, the plasma pileup along the overlying coronal loops corresponds to the bright front, and the low-density zone between them appears as the dark cavity in the early eruption stage. The new explanation predicts that almost 100% of normal CMEs have the three-part structure in the inner corona, which has been proved by observations (Song et al. 2023b, ApJL).