What is the stage in the life cycle of a super-massive star during which it increases in size and brightness?

The stage in the life cycle of a super-massive star during which it increases in size and brightness is known as the red supergiant phase. During this stage, the star exhausts its hydrogen fuel and begins to fuse heavier elements, leading to an expansion in size and an increase in brightness. This transformation occurs after the star has gone through the main sequence phase and has entered the process of helium burning as well as subsequent stages where it fuses elements such as carbon and oxygen.

The immense gravitational forces within a super-massive star lead to the outer layers expanding significantly, causing the star to become a red supergiant. This type of star is characterized by its large radius and the distinct red color that results from lower surface temperatures compared to earlier stages.

In contrast, a red giant refers to a slightly less massive star that has undergone a similar but less dramatic expansion. A white dwarf is the remnant of a star that has exhausted its nuclear fuel and collapsed, leading to a much smaller and dimmer state. A supernova occurs at the end of a massive star’s life when it explodes violently, which is not a phase where the star increases in size and brightness, but rather a catastrophic event marking its death.