What characteristic does a supernova exhibit?

A supernova is characterized by extreme luminosity, which refers to the enormous amount of light and energy released during the explosion of a star. This event can outshine entire galaxies for a short period, making supernovae some of the brightest objects in the universe. The extreme luminosity occurs as a result of a rapid release of energy from the nuclear fusion processes and gravitational collapse that happen when a star reaches the end of its life cycle, either from exhausting its nuclear fuel or from accumulating enough mass to trigger rapid fusion.

The other characteristics do not accurately define a supernova. Steady brightness is not applicable because supernovae are transient events, typically shining intensely for a short duration before fading away. Rapid cooling may be observed in the aftermath of a supernova as the remnant cools; however, the significant defining feature is its luminosity at peak brightness. Fluctuating mass is not a characteristic of a supernova itself; while stars can have variations in mass over their lifetimes, supernovae represent a definitive moment rather than an ongoing fluctuation.