It is generally believed that double-peaked broad emission lines originate from an elliptical disk. Appearance or disappearance of the broad Balmer emission lines correspond to type 1 and type 2 active galactic nuclei (AGNs), respectively. Hence, the name changing-look AGN.
Click here for original story, Researchers find stratified structure in broad-line region for changing-look active galactic nuclei
Source: Phys.org