What factor solely determines if a star will become a supernova?

The key factor that determines whether a star will become a supernova is its mass. In the lifecycle of a star, mass plays a crucial role in its evolution and ultimate fate. Massive stars, typically those with a mass greater than eight times that of the Sun, undergo a series of nuclear fusion reactions in their cores, creating heavier elements until they reach iron. Once iron is formed, fusion no longer produces energy, leading to collapse under gravity, which ultimately results in a supernova explosion.

For less massive stars, they do not reach the conditions necessary to undergo a supernova; instead, they end their lives as white dwarfs after expelling their outer layers as planetary nebulae. Therefore, the mass of a star directly affects its capacity to explode as a supernova, making it the definitive factor in this context.