Contact binary

In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overcontact binary.[1][2][3][4] Almost all known contact binary systems are eclipsing binaries;[5] eclipsing contact binaries are known as W Ursae Majoris variables, after their type star, W Ursae Majoris.[6]

Contact binaries are not to be confused with common envelopes. Whereas the configuration of two touching stars in a contact binary has a typical lifetime of millions to billions of years, the common envelope is a dynamically unstable phase in binary evolution that either expels the stellar envelope or merges the binary in a timescale of months to years.[7]

An artist’s impression of the hottest and most massive touching double star
Artist's rendering of VFTS 352 contact binary star

See also


  1. ^ Darling, David. "binary star". Retrieved 2019-05-06.
  2. ^ contact binary, David Darling, The Internet Encyclopedia of Science. Accessed on line November 4, 2007.
  3. ^ overcontact binary, David Darling, The Internet Encyclopedia of Science. Accessed on line November 4, 2007.
  4. ^ pp. 51–53, An Introduction to Astrophysical Fluid Dynamics, Michael J. Thompson, London: Imperial College Press, 2006. ISBN 1-86094-615-1.
  5. ^ p. 231, Stellar Rotation, Jean Louis Tassoul, Andrew King, Douglas Lin, Stephen P. Maran, Jim Pringle, and Martin Ward, Cambridge, UK, New York: Cambridge University Press, 2000. ISBN 0-521-77218-4.
  6. ^ p. 19, Double and Multiple Stars and how to Observe Them, James Mullaney, New York, London: Springer, 2005. ISBN 1-85233-751-6.
  7. ^ Ivanova, N.; Justham, S.; Chen, X.; De Marco, O.; Fryer, C. L.; Gaburov, E.; Ge, H.; Glebbeek, E.; Han, Z.; Li, X. D.; Lu, G.; Podsiadlowski, P.; Potter, A.; Soker, N.; Taam, R.; Tauris, T. M.; van den Heuvel, E. P. J.; Webbink, R. F. (2013). "Common envelope evolution: where we stand and how we can move forward". The Astronomy and Astrophysics Review. 21: 59. arXiv:1209.4302. Bibcode:2013A&ARv..21...59I. doi:10.1007/s00159-013-0059-2.
(192642) 1999 RD32

(192642) 1999 RD32, provisional designation 1999 RD32, is an eccentric asteroid and suspected contact binary, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 5 kilometers in diameter. It was discovered on 8 September 1999, at a magnitude of 18, by astronomers of the LINEAR program using its 1-meter telescope at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, United States. The asteroid is likely of carbonaceous composition and has a rotation period of 17.08 hours.

(388188) 2006 DP14

(388188) 2006 DP14, provisional designation 2006 DP14, is a sub-kilometer sized, peanut-shaped asteroid on a highly eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group. This contact binary was discovered on 23 February 2006, by astronomers of the LINEAR program at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. On 10 February 2014, it passed 6.25 lunar distances from Earth. The asteroid is approximately 400 meters in diameter and has a rotation period of 5.77 hours.

(85989) 1999 JD6

(85989) 1999 JD6 is an Aten asteroid, near-Earth object, and potentially hazardous object in the inner Solar System that makes frequent close approaches to Earth and Venus. On the Earth approach in 2015, it was observed by the Goldstone Solar System Radar and found to be a contact binary with the largest axis approximately 2 kilometers wide, and each lobe about 200–300 meters large. Although 1999 JD6 in its current orbit never passes closer than 0.047 AU to Earth, it is listed as a potentially hazardous object because it is large and might pose a threat in the future.

The asteroid is well-observed, having been observed over 2,000 times over a length of over 25 years, and was assigned a numeric designation in August 2004.

11066 Sigurd

11066 Sigurd, provisional designation 1992 CC1, is a stony, rare-type asteroid and elongated contact binary, classified as near-Earth object of the Apollo group of asteroids, approximately 2.5 kilometers in diameter.

It was discovered on 9 February 1992, by American astronomer couple Carolyn and Eugene Shoemaker at Palomar Observatory, California, and named after Sigurd, a hero from Norse mythology.

2007 TU24

2007 TU24 is an Apollo near-Earth asteroid that was discovered by the Catalina Sky Survey in Arizona on October 11, 2007. Imaging radar has estimated that it is 250 meters (820 ft) in diameter. The asteroid passed 554,209 kilometer (344,370 mile or 1.4-lunar distance) from Earth on January 29, 2008, at 08:33 UTC. (At the time of the passage it was believed the closest for any known potentially hazardous asteroid (PHA) of this size before 2027, but in 2010 2005 YU55 was measured to be 400 meters in diameter.) At closest approach the asteroid had an apparent magnitude of 10.3 and was about 50 times fainter than the naked eye can see. It required about a 3-inch (76 mm) telescope to be seen.

2014 HQ124

2014 HQ124 is a sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Aten group, approximately 370 meters (1,210 ft) in diameter. It passed 3.25 lunar distances (LD) from Earth on 8 June 2014. It was discovered on 23 April 2014 by NEOWISE. It is estimated that an impact event would have had the energy equivalent of 2,000 megatons of TNT and would have created a 5 km (3 mi) impact crater. The news media misleadingly nicknamed it, The Beast. 2014 HQ124 previously passed this close to Earth in 1952 and will not again until at least 2307. Radar imaging suggests it may be a contact binary.

2014 JO25

2014 JO25 is a near-Earth asteroid. It was discovered in May 2014 by astronomers at the Catalina Sky Survey near Tucson, Arizona - a project of NASA's NEO (Near Earth Object) Observations Program in collaboration with the University of Arizona.

2063 Bacchus

2063 Bacchus ( BAK-əs), provisional designation 1977 HB, is a stony asteroid and near-Earth object of the Apollo group, approximately 1 kilometer in diameter. The contact binary was discovered on 24 April 1977, by American astronomer Charles Kowal at the Palomar Observatory in California, United States. It was named after Bacchus from Roman mythology.

4450 Pan

4450 Pan, provisional designation 1987 SY, is a highly eccentric asteroid and contact binary, classified as a potentially hazardous asteroid and near-Earth object of the Apollo group, approximately 1.1 kilometers in diameter.

The asteroid was discovered on 25 September 1987, by American astronomers Eugene and Carolyn Shoemaker at Palomar Observatory in California, United States. It was named after Pan from Greek mythology.

4486 Mithra

4486 Mithra, provisional designation 1987 SB, is an eccentric asteroid and suspected contact-binary, classified as near-Earth object and potentially hazardous asteroid, approximately 2 kilometers in diameter. It belongs to the Apollo group of asteroids and is a relatively slow rotator.

The asteroid was discovered on 22 September 1987, by Belgian astronomer Eric Elst and Bulgarian astronomer Vladimir Shkodrov at Rozhen Observatory, in the Smolyan Province of Bulgaria. It was named after the Indo-Iranian divinity Mithra.

4769 Castalia

The asteroid 4769 Castalia ( kə-STAY-lee-ə; previously known by the provisional designation 1989 PB) is an asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 1.4 kilometer in diameter. It was the first asteroid to be modeled by radar imaging. It was discovered on 9 August 1989, by American astronomer Eleanor Helin (Caltech) on photographic plates taken at Palomar Observatory in California. It is named after Castalia, a nymph in Greek mythology. It is also a Mars- and Venus-crosser asteroid.

624 Hektor

624 Hektor ( HEK-tor) is the largest Jupiter trojan and the namesake of the Hektor family, with a highly elongated shape equivalent in volume to a sphere of approximately 225 to 250 kilometers diameter. It was discovered on 10 February 1907, by astronomer August Kopff at Heidelberg Observatory in southwest Germany, and named after the Trojan prince Hector, from Greek mythology. It has one small 12-kilometer sized satellite, Skamandrios, discovered in 2006.


8P/Tuttle (also known as Tuttle's Comet or Comet Tuttle) is a periodic comet in the Solar System. It fits the classical definition of a Jupiter-family comet with an orbital period of less than 20 years, but does not fit the modern definition of (2 < TJupiter< 3). Perihelion was late January 2008, and as of February was visible telescopically to Southern Hemisphere observers in the constellation Eridanus. On December 30, 2007 it was in close conjunction with spiral galaxy M33. On January 1, 2008 it passed Earth at a distance of 0.25282 AU (37,821,000 km; 23,501,000 mi).Comet 8P/Tuttle is responsible for the Ursid meteor shower in late December.Predictions that the 2007 Ursid meteor shower could be expected to be stronger than usual due to the return of the comet, did not appear to materialize, as counts were in the range of normal distribution.

AB Andromedae

AB Andromedae (AB And) is a binary star in the constellation Andromeda. Its maximum apparent visual magnitude is 9.49 but shows a variation in brightness down to a magnitude of 10.46 in a periodic cycle of roughly 8 hours. The observed variability is typical of W Ursae Majoris variable stars, so the two stars in this system form a contact binary.

Common envelope

In astronomy, a common envelope (CE) is gas that contains a binary star system. The gas does not rotate at the same rate as the embedded binary system. A system with such a configuration is said to be in a common envelope phase or undergoing common envelope evolution.

During a common envelope phase the embedded binary system is subject to drag forces from the envelope which cause the separation of the two stars to decrease. The phase ends either when the envelope is ejected to leave the binary system with much smaller orbital separation, or when the two stars become sufficiently close to merge and form a single star. A common envelope phase is short-lived relative to the lifetime of the stars involved.

Evolution through a common envelope phase with ejection of the envelope can lead to the formation of a binary system composed of a compact object with a close companion. Cataclysmic variables, X-ray binaries and systems of close double white dwarfs or neutron stars are examples of systems of this type which can be explained as having undergone common envelope evolution. In all these examples there is a compact remnant (a white dwarf, neutron star or black hole) which must have been the core of a star which was much larger than the current orbital separation. If these systems have undergone common envelope evolution then their present close separation is explained. Short-period systems containing compact objects are sources of gravitational waves and Type Ia supernovae.

Predictions of the outcome of common envelope evolution are uncertain.A common envelope is sometimes confused with a contact binary. In a common envelope binary system the envelope does not generally rotate at the same rate as the embedded binary system; thus it is not constrained by the equipotential surface passing through the L2 Lagrangian point. In a contact binary system the shared envelope rotates with the binary system and fills an equipotential surface.

Contact binary (small Solar System body)

A contact binary is a small Solar System body such as a minor planet or a comet, that is composed of two bodies that have gravitated toward each other until they touch, resulting in a bilobated, peanut-like overall shape. Contact binaries are often rubble piles but distinct from real binary systems such as binary asteroids. The term is also used for stellar contact binaries.


Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.

A widely accepted theory of planet formation, the so-called planetesimal hypotheses, the Chamberlin–Moulton planetesimal hypothesis and that of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger bodies. When the bodies reach sizes of approximately one kilometer, then they can attract each other directly through their mutual gravity, enormously aiding further growth into moon-sized protoplanets. This is how planetesimals are often defined. Bodies that are smaller than planetesimals must rely on Brownian motion or turbulent motions in the gas to cause the collisions that can lead to sticking. Alternatively, planetesimals may form in a very dense layer of dust grains that undergoes a collective gravitational instability in the mid-plane of a protoplanetary disk or via the concentration and gravitational collapse of swarms of larger particles in streaming instabilities. Many planetesimals eventually break apart during violent collisions, as may have happened to 4 Vesta and 90 Antiope, but a few of the largest planetesimals may survive such encounters and continue to grow into protoplanets and later planets.

It is generally thought that about 3.8 billion years ago, after a period known as the Late Heavy Bombardment, most of the planetesimals within the Solar System had either been ejected from the Solar System entirely, into distant eccentric orbits such as the Oort cloud, or had collided with larger objects due to the regular gravitational nudges from the giant planets (particularly Jupiter and Neptune). A few planetesimals may have been captured as moons, such as Phobos and Deimos (the moons of Mars) and many of the small high-inclination moons of the giant planets.

Planetesimals that have survived to the current day are valuable to science because they contain information about the formation of the Solar System. Although their exteriors are subjected to intense solar radiation that can alter their chemistry, their interiors contain pristine material essentially untouched since the planetesimal was formed. This makes each planetesimal a 'time capsule', and their composition might reveal the conditions in the Solar Nebula from which our planetary system was formed. The most primitive planetesimals visited by spacecraft are the contact binary 2014 MU69.

SV Centauri

SV Centauri is a variable star in the constellation Centaurus. An eclipsing binary, its visual apparent magnitude has a maximum of 8.71, fading to 9.98 during primary eclipse and 9.42 during secondary eclipse. From its brightness, it's estimated to be around 6,000 light-years (1,800 parsecs) away from Earth. Parallax measurements from Gaia Data Release 2 yield a similar distance of around 2,100 pc.SV Centauri is a contact binary made of two hot B-type stars with spectral types of B1V and B6.5III and effective temperatures of 23,000 and 14,000 K. The primary component, the brighter star with 11,700 times the solar luminosity, is the less massive one with 7.7 times the solar mass and has a radius of 6.8 times the solar radius. The secondary component has a mass equal to 9.6 solar masses, radius of 7.4 solar radii and a brightness 1,900 times larger than the Sun's. The separation between the center of each star is only 15.3 solar radii. The system is viewed from a high inclination of 81.8°.The orbital period of SV Centauri is monotonically decreasing at a very fast mean rate of 2.1 seconds per year, the largest rate for any known system. The first observations of the system, in 1894, revealed a period of 1.6606 days, which decreased to 1.6581 days in 1993, showing a decrease rate that is variable with time, but with time intervals of 10-30 years when it is constant. The transition between such intervals of constant change can be accompanied by very fast decreases in the period, such as of 15 seconds per year in 1975.The most probable explanation for the period decrease is mass transfer from the less massive to the more massive star and subsequent mass loss through the L3 Lagrangian point of the system, which is located on the outer side of the more massive star. The mass loss causes loss of angular momentum, which is compensated by a decrease in the separation between the stars. In this model, the system is losing mass at a rate of about 5 ×10−5 solar masses per year; the variation of this rate causes the variation in the rate of period decrease. The alternative possibility is mass transfer from the more massive to the less massive star, which naturally tends to decrease the orbital period. This may create an accretion disk around the less massive star, similar to Beta Lyrae.

V1309 Scorpii

V1309 Scorpii (also known as V1309 Sco) is a contact binary that merged into a single star in 2008 in a process known as a luminous red nova. It was the first star to provide conclusive evidence that contact binary systems end their evolution in a stellar merger. Its similarities to V838 Monocerotis and V4332 Sagittarii allowed scientists to identify these stars as merged contact binaries as well.

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