Binary star

A binary star is two stars which orbit around each other. For each star, the other is its companion star. Many stars are part of a system with two or more stars. The brighter star is called the primary star, and the other is the secondary star.

Binary stars are important in astrophysics because looking at their orbits allows scientists to find out their masses. From this, scientists found the mass–luminosity relationship, and used it to find the masses of single stars.

Binary stars are not the same as line-of-sight optical double stars, which look close together but are not connected by gravity. Optical double stars may actually be far apart in space, but binary stars are quite close together. The first person to discover and prove true binary stars was the Anglo-German astronomer William Herschel. He published the first catalogue of binary stars, and his son John Herschel found several thousand more and updated the catalogue.^[1] John Michell first suggested that double stars might be physically attached to each other when he argued in 1767 that the probability that a double star was due to a chance alignment was small. ^[2][3] William Herschel began observing double stars in 1779 and soon after that he published catalogs of about 700 double stars.^[4]

1. ↑ Buttmann, Gunther 1974. In the shadow of the telescope: a biography of John Herschel. Lutterworth, Guilford. p50 & 197
2. ↑ pp. 10–11, Observing and Measuring Double Stars, Bob Argyle, ed., London: Springer, 2004, ISBN 1-85233-558-0.
3. ↑ Michell, John (1767). "An Inquiry into the Probable Parallax, and Magnitude of the Fixed Stars, from the Quantity of Light Which They Afford us, and the Particular Circumstances of Their Situation, by the Rev. John Michell, B. D. F. R. S". Philosophical Transactions. 57. pp. 249–250. Bibcode:1767RSPT...57..234M. JSTOR 105952.
4. ↑ Heintz, W. D. (1978). Double Stars. Dordrecht: D. Reidel Publishing Company. p. 4. ISBN 978-90-277-0885-4.