What type of star is characterized by its huge mass and a lifecycle that leads it to expand into a red supergiant?

A supermassive star is characterized by its enormous mass, typically exceeding eight times that of the Sun. These stars evolve through a lifecycle that is markedly different from smaller stars. As they burn through their nuclear fuel, they expand and become red supergiants. This expansion happens because, as the core of the star undergoes fusion of heavier elements, it generates substantial energy that pushes against the gravitational collapse, causing the outer layers to balloon outward.

In contrast, medium-sized stars, such as our Sun, have a different evolutionary path and do not reach the red supergiant stage. Dwarf stars, which include white dwarfs and red dwarfs, also do not possess the mass or the conditions necessary to undergo the dramatic expansion seen in supermassive stars. Lastly, while binary stars are systems that consist of two stars orbiting around a common center, the term does not pertain to the mass and lifecycle traits described in the question. Therefore, the unique characteristics of supermassive stars are what clearly define their lifecycle culminating in the expansion into red supergiants.