Binary star

Binary Star

A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called multiple star systems. These systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means.

Overview

Binary stars are of immense importance to astronomers as they provide the best method of determining the masses of stars. This is critical to the understanding of stellar evolution. A binary star system is the simplest type of multiple star system. In a binary star system, the brighter star is officially classified as the primary star, while the dimmer of the two is the secondary.

Formation

Binary stars may be formed in one of three ways. The first, and most common, is through the formation of a star within a dense gas cloud. The second method is through gravitational capture between two stars in a star cluster. The third method is through the breakup of a triple star system.

Types of Binary Stars

There are several types of binary stars, classified by how they are observed. These include visual binaries, spectroscopic binaries, eclipsing binaries, astrometric binaries, and X-ray binaries.

Visual Binaries

Visual binaries are two stars that can be seen to be separate through a telescope. The brighter star of a visual binary is the primary star, and the dimmer is its secondary.

Spectroscopic Binaries

Spectroscopic binaries are binary star systems that are not visually separable but the spectral lines of the two stars differ in velocity, indicating orbital motion.

Eclipsing Binaries

Eclipsing binaries are binary stars systems in which the orbital plane lies so nearly in the line of sight that the stars eclipse each other.

Astrometric Binaries

Astrometric binaries are binary star systems where only one star can be seen and the other inferred by its gravitational influence on the visible star.

X-ray Binaries

X-ray binaries are binary star systems that emit X-rays. The emission is thought to result from processes near the surface of the neutron star or black hole.

See Also

• Star
• Star system
• Star formation
• Star cluster