Examples of binaries are Sirius, and Cygnus X-1 (Cygnus X-1 being a well-known black hole). In some cases, these close binary systems can exchange mass, which may bring their evolution to stages that single stars cannot attain. If components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other these pairs are called eclipsing binaries, or, together with other binaries that change brightness as they orbit, photometric binaries. They may also be detected by indirect techniques, such as spectroscopy ( spectroscopic binaries) or astrometry ( astrometric binaries).

Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in which case they are called visual binaries. For the hip hop group, see Binary Star (hip hop group).Ī binary star is a system of two stars that are gravitationally bound to and in orbit around each other.

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