Binary Star Systems

Many stars are not born alone. Roughly half of all Sun-like stars have at least one companion, so binary and multiple star systems are nearly as common as single stars (surveys still debate the exact split). Binary stars form when a collapsing cloud fragment has enough angular momentum to split into two separate cores.

Binary systems come in many configurations. Close binaries can exchange material, leading to novae and Type Ia supernovae. Wide binaries orbit each other at distances of hundreds of AU, barely interacting. Some systems contain three, four, or even seven stars in complex orbital dances.