What astronomical event occurs after the red giant phase in a star's life cycle for massive stars?

During the life cycle of massive stars, after they have exhausted their nuclear fuel and entered the red giant phase, they undergo a dramatic change that culminates in a supernova explosion. This event occurs when the core of the massive star becomes so dense and hot that it can no longer support the weight of the outer layers. As a result, the core collapses, and the outer layers are expelled into space in a cataclysmic explosion.

This supernova not only marks the end of the star's life but also plays a critical role in the universe by dispersing heavy elements synthesized during the star's lifetime into the surrounding space, which can subsequently contribute to the formation of new stars and planets.

In contrast, protostar formation is an earlier stage in the life cycle of a star, occurring before nuclear fusion begins. White dwarf collapse refers to the fate of smaller stars and is related to lower-mass stars that have already gone through their own lifecycle, ultimately shedding their outer layers to leave behind a dense core. Black hole formation, while a possible outcome for the most massive stars, occurs after the supernova when the remains of the core may collapse under their own gravity if they exceed the critical mass. Therefore, the sequence of events clearly underscores