 | |
| Discovery | |
|---|---|
| Discovered by | SPHERE |
| Discovery date | 2021 |
| Direct imaging | |
| Orbital characteristics | |
| 556±17 | |
| Eccentricity | 0.4 |
| 7170±2650 | |
| Inclination | 157±128 |
| Star | b Centauri |
| Physical characteristics | |
Mean radius | 1.11 RJ |
| Mass | 10.9±1.6 MJ |
b Centauri b (sometimes b Centauri (AB) b) is a circumbinary planet orbiting the binary star system b Centauri, located in the southern constellation Centaurus. With a mass of 10.9 of Jupiter, it indicates that it is a super-Jupiter planet. [1]
The b Centauri system was included in the BEAST survey, which uses the SPHERE instrument at the Very Large Telescope to search for planets around B-type stars in the Scorpius–Centaurus association. SPHERE is equipped with a sophisticated coronagraph that blocks out the light from a star and allows exoplanets around it to be directly imaged. [2] The first observation of the system in 2019 revealed an object at a 5.3 arcseconds separation that had infrared colors consistent with a massive planet. A second observation in 2021 confirmed that the object has common proper motion with b Centauri and therefore is physically bound to the system. [3] The authors of this study also looked for old observations of b Centauri and found that the planet had been imaged by the ESO 3.6 m Telescope in 2000, but was considered a background star at the time. [3] [4] With a primary star mass of 5–6 M☉ and a total system mass of 6–10 M☉, b Centauri is the most massive system around which a planet has been found; previously, the most massive star with a known planet was 3 M☉. The discovery was published in December 2021 on the scientific journal Nature and was led by Stockholm University astronomer Markus Janson. [3]
Named b Centauri (AB)b (shortened as 'b Cen (AB)b'), this is a circumbinary planet that orbits the stellar pair at a projected separation of 560 AU. The three epochs of observations show evidence of the orbital motion of the planet around the central stars, but the orbit is still not well constrained. The data are consistent with an orbital period between 2650 and 7170 years, inclination between 128 and 157 degrees, and eccentricity smaller than 0.4. [3]
The SPHERE images show the planet has approximately 0.01% the solar luminosity, a relic of its recent formation. From this luminosity and the age of the system, cooling models predict it has a mass of about 11 times the mass of Jupiter. The mass ratio between b Cen (AB)b and the central binary star is 0.10—0.17%, which is similar to the Sun-Jupiter system and is consistent to the expectations that more massive stars tend to have more massive planets. [3]
The formation mechanism for b Cen (AB)b is uncertain. It is believed that most giant planets are formed via core accretion, in which a rocky core, after growing to a critical mass, starts rapidly accreting the surrounding gas of the circumstellar disc. This mechanism cannot explain b Cen (AB)b, because core accretion becomes less efficient at large distances from the star, and massive stars like b Centauri A cause the disc to dissipate much quicker. It's more probable that the planet formed directly from the circumstellar gas, through a mechanism known as gravitational instability. This process is much faster than core accretion and can act even at separations of hundreds of astronomical units. Another possibility is that the planet formed closer to the central stars and was subsequently ejected to its current orbit through interactions with another body, but this is disfavored by the lack of evidence of other planets in the system and by the low eccentricity of b Cen (AB)b. [3]
The discovery of b Cen (AB)b showed that planets can exist even around massive stars. Previous studies had shown that planet occurrence rate starts to drop for stars over 2 M☉ and reaches almost zero for 3 M☉ stars, but this result is valid only for close in planets, which the radial velocity method can detect. The discovers of b Cen (AB)b argued that the short lifetime of the circumstellar discs around massive stars may prevent planets from migrating closer to their stars, but allows the existence of distant planets like b Cen (AB)b. [3]
Alpha Centauri is a triple star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus, Toliman (B) and Proxima Centauri (C). Proxima Centauri is the closest star to the Sun at 4.2465 light-years.
HD 129116 is a binary star in the northeastern part of Centaurus, east of Menkent. It is also known by its Bayer designation of b Centauri, while HD 129116 is the star's identifier in the Henry Draper catalogue. This object has a blue-white hue and is faintly visible to the naked eye with an apparent visual magnitude of +4.01. It is located at a distance of approximately 325 light years from the Sun based on parallax, and has an absolute magnitude of −1.07.
HD 109749 is a binary star system about 206 light years away in the constellation of Centaurus. The pair have a combined apparent visual magnitude of 8.08, which is too faint to be visible to the naked eye. The primary component has a close orbiting exoplanet companion. The system is drifting closer with a heliocentric radial velocity of −13.2 km/s.
HD 59686 Ab is an exoplanet that orbits the giant star HD 59686 A in a close binary star system. It has a nearly circular orbit with a period of 300 days and a semi-major axis of 1.09 AU, slightly greater than the distance between Earth and the Sun. It has a minimum mass 6.9 times that of Jupiter, with the true mass depending on the orbital inclination, which is not yet known. HD 59686 Ab was discovered by radial velocity and first announced in November 2003, but the discovery was not formally published until 2016.
A circumbinary planet is a planet that orbits two stars instead of one. The two stars orbit each other in a binary system, while the planet typically orbits farther from the center of the system than either of the two stars. In contrast, circumstellar planets in a binary system have stable orbits around one of the two stars, closer in than the orbital distance of the other star. Studies in 2013 showed that there is a strong hint that a circumbinary planet and its stars originate from a single disk.
Kepler-16b is an exoplanet. It is a Saturn-mass planet consisting of half gas and half rock and ice, and it orbits a binary star, Kepler-16, with a period of 229 days. "[It] is the first confirmed, unambiguous example of a circumbinary planet – a planet orbiting not one, but two stars," said Josh Carter of the Center for Astrophysics | Harvard & Smithsonian, one of the discovery team.
Kepler-34 is an eclipsing binary star system in the constellation of Cygnus. Both stars have roughly the same mass as the Sun and, like the Sun, both are spectral class G. They are separated by 0.22 AU, and complete an eccentric (e=0.5) orbit around a common center of mass every 27 days.
Kepler-35 is a binary star system in the constellation of Cygnus. These stars, called Kepler-35A and Kepler-35B have masses of 89% and 81% solar masses respectively, and both are assumed to be of spectral class G. They are separated by 0.176 AU, and complete an eccentric orbit around a common center of mass every 20.73 days.
Kepler-47c is an exoplanet orbiting the binary star system Kepler-47, the outermost of three such planets discovered by NASA's Kepler spacecraft. The system, also involving two other exoplanets, is located about 3,400 light-years away.
Kepler-47b is an exoplanet orbiting the binary star system Kepler-47, the innermost of three such planets discovered by NASA's Kepler spacecraft. The system, also involving two other exoplanets, is located about 3,400 light-years away.
Planets in binary star systems may be candidates for supporting extraterrestrial life. Habitability of binary star systems is determined by many factors from a variety of sources. Typical estimates often suggest that 50% or more of all star systems are binary systems. This may be partly due to sample bias, as massive and bright stars tend to be in binaries and these are most easily observed and catalogued; a more precise analysis has suggested that the more common fainter stars are usually singular, and that up to two thirds of all stellar systems are therefore solitary.
A circumstellar disc is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the reservoirs of material out of which planets may form. Around mature stars, they indicate that planetesimal formation has taken place, and around white dwarfs, they indicate that planetary material survived the whole of stellar evolution. Such a disc can manifest itself in various ways.
Kepler-1647b is a circumbinary exoplanet that orbits the binary star system Kepler-1647, 3,700 light-years (1,100 pc) from Earth in the constellation Cygnus. It was announced on June 13, 2016, in San Diego at a meeting of the American Astronomical Society. It was detected using the transit method, when it caused the dimming of the primary star, and then again of the secondary star blended with the primary star eclipse. The first transit of the planet was identified in 2012, but at the time the single event was not enough to rule out contamination, or confirm it as a planet. It was discovered by the analysis of the Kepler light-curve, which showed the planet in transit.
OGLE-2007-BLG-349(AB)b is a circumbinary extrasolar planet about 8,000 light-years away in the constellation of Sagittarius. It is the first circumbinary exoplanet to be discovered using the microlensing method of detecting exoplanets.
GG Tauri, often abbreviated as GG Tau, is a quintuple star system in the constellation Taurus. At a distance of about 450 light years away, it is located within the Taurus-Auriga Star Forming Region. The system comprises three stars orbiting each other in a hierarchical triple system, known as GG Tauri A, and another binary star system more distant from the central system, known as GG Tauri B.
A circumplanetary disk is a torus, pancake or ring-shaped accumulation of matter composed of gas, dust, planetesimals, asteroids or collision fragments in orbit around a planet. Around the planets, they are the reservoirs of material out of which moons may form. Such a disk can manifest itself in various ways.
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HIP 79098 is a binary star in the constellation Scorpius. It has a visual apparent magnitude of +5.88, being visible to the naked eye under very dark skies. From parallax measurements by the Gaia spacecraft, it is located approximately 500 light-years from Earth.
