How do novas and supernovas differ from other variable stars?

In astronomy, stars whose brightness changes over time are known as variable stars. While many variable stars, such as pulsating variables (e.g., Cepheids), change their luminosity due to rhythmic expansion and contraction, novas and supernovas are classified as explosive or catastrophic variables.

The primary differences are as follows:

• Nature of the Event: Unlike pulsating stars, which undergo cyclical changes in size and light output, explosive variables are defined by violent, sudden outbursts caused by the loss of material or catastrophic destruction of the star.12
• Novae: These occur in binary star systems where a white dwarf pulls hydrogen-rich matter from a companion star. This accumulates on the surface, triggering a nuclear explosion that ejects outer gases. The star typically survives and may repeat this process over long intervals.34
• Supernovae: These are cataclysmic events that essentially end a star's active lifetime. In Type II supernovas, a massive star's core collapses, leading to a total explosion. In Type Ia supernovas, a white dwarf is often completely destroyed. Their energy output is vastly greater than that of a nova, often outshining an entire galaxy.5