What is the difference between a Type II supernova and a Type IIn supernova?

A Type II supernova occurs when a massive star exhausts its fuel, and its core collapses under gravity, producing a catastrophic explosion. Type II supernovae show hydrogen lines in their spectra, indicating that the explosion originated from a star with a hydrogen-rich envelope.

On the other hand, a Type IIn supernova is a type of supernova that has narrow hydrogen lines in its spectrum, indicating the presence of a dense, slow-moving envelope of material around the exploding star. Type IIn supernovae are thought to be caused by the explosion of a massive star that has previously shed a lot of material, which interacts with the outer layers of the star at the time of the explosion.

Both Type II and Type IIn supernovae are important for understanding the evolution of massive stars, and they play a significant role in the synthesis and distribution of heavy elements in the universe.