Most stars have a partner, but most star systems are single

More than half of all stars have at least one stellar partner, NASA says, yet most star systems are single: about two-thirds of the systems in the Milky Way’s disk are one lone star. Both statements hold because every pair or triple puts two or more stars into a single system, so multiples claim a bigger share of stars than of systems.

The more massive a star, the likelier it has company:

Star type	Finding	Study
O-type stars (15 or more solar masses)	75% have a close companion	Hugues Sana, ESO’s Very Large Telescope, 2012
Sun-like stars	54% are single	survey of 454 stars, 2010
Red dwarfs	only about 25% have partners	Charles Lada, Harvard-Smithsonian Center for Astrophysics, 2006

The reason is sheer numbers: red dwarfs make up roughly 85% of the Milky Way’s stars, according to the same analysis by Lada, so their solitary habits dominate the census.

That undercuts the popular line that our solitary Sun is an oddball. Most Sun-like stars are single too, and lone red dwarfs are the commonest arrangement in the galaxy. Lada’s release put it bluntly: the “common wisdom” that most systems are multiple was wrong.

Multiples are still everywhere. Systems of up to seven stars have been observed, and our nearest neighbor, Alpha Centauri, is a triple.

For massive stars, a partner changes the whole life story. Sana’s team estimated that 20–30% of O-type stars will eventually merge with their companion, and a further 40–50% will have gas pulled off them by a “vampire” partner. Because stripped and rejuvenated stars both burn hotter and bluer, galaxies full of such pairs can look younger than they really are.