Binary Star Systems

A group of astronomers and astrophysicists from multiple Chinese research institutions has recently identified a binary star system featuring a unique combination: one of the stars is a rapidly spinning millisecond pulsar, while the other consists primarily of helium.

Understanding Binary Star Systems

A binary star system consists of two stars bound together by gravity, orbiting a shared center of mass known as the barycenter. These stellar pairs often differ in characteristics such as mass, brightness, and size. In such systems, the more massive star is referred to as the primary, while its less massive counterpart is known as the secondary or companion star.

While all binary stars appear as double stars, not all double stars are genuine binary systems. Some stars only appear close together from Earth’s perspective but are actually separated by vast distances in space; these are termed optical doubles and are not gravitationally bound.

Unlike our solitary Sun, most stars are part of multiple-star systems. It is estimated that about 85% of stars exist in binary or higher-order systems. Some of these systems include one regular star and a stellar remnant — the remains of a star that has exhausted its nuclear fuel and collapsed under gravity. These remnants can be white dwarfs, neutron stars, or black holes. In older binary systems, both stars may have evolved into remnants and continue orbiting each other.

In certain binary arrangements, the stars are positioned so closely that they can transfer matter between them. This mass exchange typically happens when one star’s size is comparable to the distance between the two, leading to the flow of material from one star to its companion.