What is the opposite of nova?

Answer 1

The opposite of a nova, which is a sudden brightening of a star due to a thermonuclear explosion on its surface, could be considered a black hole. A black hole represents the end stage of a massive star's life cycle, where it collapses under its own gravity and cannot emit light. Alternatively, one might think of a star undergoing dimming or fading, such as a red giant transitioning to a white dwarf, as a contrasting process to the explosive brightness of a nova.