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

Supernovae are among the most dramatic and powerful events in the universe, and they occur when a massive star runs out of fuel and collapses. Type I and Type IIa supernovae are two distinct types of supernovae that differ in their causes and characteristics.

Type I supernovae occur when a white dwarf star in a binary system accretes matter from its companion star, causing it to exceed the Chandrasekhar limit and undergo a runaway fusion process that destroys the star. They do not contain hydrogen in their spectra, and are further divided into subtypes based on their spectral features.

Type IIa supernovae, on the other hand, occur when a massive star runs out of fuel and undergoes core collapse. They contain hydrogen in their spectra and are characterized by a plateau in their light curve, which is thought to be caused by the recombination of ionized hydrogen in the star's expanding envelope.

Understanding the differences between these two types of supernovae is important for astronomers, as they can provide clues about the evolution of stars and the properties of the universe.