What is the difference between a Type I and Type IIb supernova?

A supernova is an astronomical event that occurs at the end of a star's life cycle. It is a powerful and luminous explosion that releases an enormous amount of energy, and can briefly outshine an entire galaxy. Supernovae are classified based on their spectral features, specifically the presence or absence of certain atomic lines. The two main types of supernovae are Type I and Type II.

Type I supernovae are further divided into subtypes Ia, Ib, and Ic. They are characterized by the absence of hydrogen lines in their spectra. Type Ia supernovae are thought to occur in binary systems where one star is a white dwarf. When the white dwarf accretes enough material from its companion, it undergoes a runaway nuclear fusion reaction, causing a thermonuclear explosion.

Type II supernovae, on the other hand, have hydrogen lines in their spectra. They are thought to occur in massive stars that have exhausted their nuclear fuel and collapsed under their own gravity. Type II supernovae are further divided into subtypes II-P, II-L, IIb, and IIn. Type IIb supernovae are similar to Type II-L, but with a weaker hydrogen line. This could indicate that the star had lost some of its hydrogen envelope before the explosion, or that the explosion had blown off the outer layers of the star, leaving only the helium core behind.