binary stars

Cataclysmic variables are close binary stars in which a white dwarf pulls gas off a companion. The result is outbursts that range from dwarf novae flaring every few weeks to classical novae that brighten by up to a million times. This article explains the physics, the period gap, and the famous systems.

Roughly 44% of Sun-like stars have a companion, and the share climbs past 80% for the most massive stars. Binary stars let astronomers weigh stars, produce Type Ia supernovae and millisecond pulsars, and generate the gravitational waves LIGO detects.

Most stars in the galaxy are in binary systems. If our solar system had two suns, Earth's orbit might be stable — or chaotic. The climate would be stranger, the sky alien, and the evolution of life might have gone very differently.