SN IIb

Supernova SN IIb is a type of stellar explosion that occurs when a massive star has lost most, but not all, of its outer hydrogen layers before collapsing. These supernovae initially display features similar to Type II supernovae, with some hydrogen in their spectrum, but later their spectra resemble Type Ib, which lack hydrogen. This transition indicates the star had a thin hydrogen shell remaining. SN IIb explosions provide insight into stellar evolution, especially how massive stars shed their outer layers through winds or interactions with companion stars before ending their lives in a dramatic explosion.