Final answer:
Stars consume nuclear fuel to sustain fusion reactions. Their ability to do so depends on their mass and composition, with massive stars consuming and radiating energy until they exhaust their nuclear fuel, eventually leading to their collapse.
Step-by-step explanation:
Stars with the right overall mass and composition are capable of sustaining nuclear fusion reactions, which enables them to consume their nuclear fuel and maintain equilibrium. The structure and characteristics of main-sequence stars can be understood by two key factors: their total mass and their composition. For instance, objects with extremely low mass, known as brown dwarfs or planets, never reach the necessary central temperatures to start nuclear reactions. On the other hand, massive stars can have masses up to 100 to 200 times that of our Sun. These massive stars eventually stop gathering matter because of the intense energy they radiate. Like all stars, they will exhaust their nuclear fuel over time, leading to the end of their lifecycle.
As an example, within the Sun, 600 million tons of hydrogen fuse into helium every second, with 4 million tons converting into energy. This illustrates the concept that stars are not infinite; they are ultimately limited by the amount of nuclear fuel they can consume. Once a star exhausts its nuclear fuel, it can no longer produce the pressure needed to support itself against gravitational collapse.