Final answer:
Massive stars at the end of their life can become white dwarfs, neutron stars, or black holes, depending on the mass of their core after fuel exhaustion.
Step-by-step explanation:
Near the end of the life of a massive star, several outcomes are possible based on the mass of the star's core after it has exhausted its fuel. Stars with core masses less than 1.4 times that of the Sun (Msun) will end their lives as white dwarfs. Those with core masses between 1.4 and about 3 Msun often become neutron stars, which may be observable as pulsars if they emit beams of radiation. However, for the most massive stars, with core masses greater than approximately 3 Msun, not even neutron degeneracy pressure can counteract the gravitational collapse. These stars are predicted to continue collapsing until they form black holes, one of the most enigmatic and extreme objects in the universe.