# B Centauri b

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Long-period exoplanet orbiting b Centauri

This article is about the exoplanet b Centauri b. For the stars "β Centauri B" and "β Centauri AB", see [Beta Centauri](/source/Beta_Centauri).

b Centauri b b Centauri imaged by VLT/SPHERE. The planet b Centauri b is indicated by an arrow. Discovery Discovered by SPHERE Discovery date 2021 Detection method Direct imaging Orbital characteristics Semi-major axis 556±17 AU Eccentricity 0.4 Orbital period (sidereal) 7170±2650 years 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](/source/Circumbinary_planet) orbiting the binary star system [b Centauri](/source/HD_129116), located in the southern constellation [Centaurus](/source/Centaurus). The planet is a [super-Jupiter](/source/Super-Jupiter), with a mass 10.9 times [that of Jupiter](/source/Jupiter_mass).[1]

## Discovery

Artist's impression showing b Centauri b. b Centauri is in the background.

The b Centauri system was included in the BEAST survey, which uses the [SPHERE](/source/SPHERE) instrument at the [Very Large Telescope](/source/Very_Large_Telescope) to search for planets around B-type stars in the Scorpius–Centaurus association. SPHERE is equipped with a sophisticated [coronagraph](/source/Coronagraph) that blocks out the light from a star and allows exoplanets around it to be [directly imaged](/source/Direct_imaging).[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](/source/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](/source/Nature_(journal))* and was led by [Stockholm University](/source/Stockholm_University) astronomer Markus Janson.[3]

Named b Centauri (AB)b (shortened as 'b Cen (AB)b'), it is a [circumbinary planet](/source/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](/source/Orbital_period) between 2650 and 7170 years, inclination between 128 and 157 degrees, and [eccentricity](/source/Orbital_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](/source/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]

## Formation

The formation mechanism for b Cen (AB)b is uncertain. It is believed that most giant planets are formed via [core accretion](/source/Core-accretion_theory), in which a rocky core, after growing to a critical mass, starts rapidly [accreting](/source/Accretion_(astrophysics)) the surrounding gas of the [circumstellar disc](/source/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 is 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](/source/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](/source/Planetary_migration) closer to their stars, but allows the existence of distant planets like b Cen (AB)b.[3]

## References

1. **[^](#cite_ref-1)** ["Exoplanet-catalog"](https://exoplanets.nasa.gov/exoplanet-catalog/8381/b-centauri-ab-b/). *Exoplanet Exploration: Planets Beyond our Solar System (NASA)*. Retrieved 2023-10-24.

1. **[^](#cite_ref-Janson2021beast_2-0)** Janson, Markus; et al. (2021). "BEAST begins: Sample characteristics and survey performance of the B-star Exoplanet Abundance Study". *Astronomy and Astrophysics*. **646**: A164. [arXiv](/source/ArXiv_(identifier)):[2101.02043](https://arxiv.org/abs/2101.02043). [Bibcode](/source/Bibcode_(identifier)):[2021A&A...646A.164J](https://ui.adsabs.harvard.edu/abs/2021A&A...646A.164J). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202039683](https://doi.org/10.1051%2F0004-6361%2F202039683). [S2CID](/source/S2CID_(identifier)) [230770142](https://api.semanticscholar.org/CorpusID:230770142).

1. ^ [***a***](#cite_ref-Janson2021_3-0) [***b***](#cite_ref-Janson2021_3-1) [***c***](#cite_ref-Janson2021_3-2) [***d***](#cite_ref-Janson2021_3-3) [***e***](#cite_ref-Janson2021_3-4) [***f***](#cite_ref-Janson2021_3-5) [***g***](#cite_ref-Janson2021_3-6) Janson, Markus; et al. (2021). "A wide-orbit giant planet in the high-mass b Centauri binary system". *Nature*. **600** (7888): 231–234. [arXiv](/source/ArXiv_(identifier)):[2112.04833](https://arxiv.org/abs/2112.04833). [Bibcode](/source/Bibcode_(identifier)):[2021Natur.600..231J](https://ui.adsabs.harvard.edu/abs/2021Natur.600..231J). [doi](/source/Doi_(identifier)):[10.1038/s41586-021-04124-8](https://doi.org/10.1038%2Fs41586-021-04124-8). [PMID](/source/PMID_(identifier)) [34880428](https://pubmed.ncbi.nlm.nih.gov/34880428). [S2CID](/source/S2CID_(identifier)) [245005994](https://api.semanticscholar.org/CorpusID:245005994).

1. **[^](#cite_ref-Shatsky2002_4-0)** Shatsky, N.; Tokovinin, A. (2002). "The mass ratio distribution of B-type visual binaries in the Sco OB2 association". *Astronomy and Astrophysics*. **382**: 92. [arXiv](/source/ArXiv_(identifier)):[astro-ph/0109456](https://arxiv.org/abs/astro-ph/0109456). [Bibcode](/source/Bibcode_(identifier)):[2002A&A...382...92S](https://ui.adsabs.harvard.edu/abs/2002A&A...382...92S). [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20011542](https://doi.org/10.1051%2F0004-6361%3A20011542). [S2CID](/source/S2CID_(identifier)) [16697655](https://api.semanticscholar.org/CorpusID:16697655).

v t e Constellation of Centaurus List of stars in Centaurus Centaurus in Chinese astronomy Stars Bayer α A (Rigil Kentaurus) B (Toliman) C (Proxima Centauri) β (Hadar) γ δ ε ζ (Leepwal) η θ (Menkent) ι (Kulou) κ λ μ ν (Heng) ξ1 ξ2 ο1 ο2 π ρ σ τ υ1 υ2 φ χ ψ x1 x2 C3 D E F G H J K M N Q Flamsteed 1 (i) 2 (g) 3 (k) 4 (h) Variable R T V Y RR SV SX BV DY UY V346 V553 V744 V752 V761 (a) V763 (C1) V766 V779 (Krzemiński's star) V803 V810 V816 (Przybylski's Star) V831 V842 V885 V886 V863 V1032 V1369 V1400 V1935 HR 4460 (A) 4466 (C2) 4499 4522 4523 4537 (j) 4546 (B) 4721 4748 (u) 4796 4817 (l) 4831 (w) 4874 (p) 4888 (e) 4889 (n) 4940 (f) 4979 4989 5006 (r) 5041 (m) 5089 (d) 5174 (z) 5222 (y) 5224 5241 5297 5358 (v) 5371 5471 (b) 5485 (c1) 5489 (c2) HD 97413 98176 100453 101581 101930 102117 (Uklun) 103197 107914 108236 109749 110113 113538 113766 114386 114729 115600 116434 (Matza) 117207 117618 (Dofida) 117939 120411 121228 121504 124448 (Popper's Star) 125072 125595 131399 Other 2MASS J1126−5003 2M1207 Gaia BH2 HD 131399 Ab PSR B1259−63 PSR J1311−3430 TOI-763 WASP-15 (Nyamien) WASP-41 WASP-42 WASP-167/KELT-13 Exoplanets 2M1207b b Centauri b HD 101930 b HD 102117 b (Leklsullun) HD 103197 b HD 109749 b HD 113538 b c HD 114386 b HD 114729 b HD 117207 b HD 117618 b (Noifasui) HD 121504 b HIP 65426 b (Najsakopajk) HIP 67522 b NGTS-13b Proxima Centauri b c d WASP-15b (Asye) Star clusters NGC 3766 4230 4507 5281 5286 5316 5460 5617 5662 Other IC 2944 ω Centauri Scorpius–Centaurus association Stock 16 Nebulae NGC 3918 5307 Other Boomerang Nebula Fleming 1 G292.0+1.8 G306.3-0.9 Gum 41 IC 2944 IRAS 13208−6020 RCW 79 RCW 86 Southern Crab Nebula SuWt 2 Galaxies NGC 3557 3568 3749 3783 4444 4603 4622 4650A 4683 4696 4706 4709 4729 4730 4743 4744 4909 4930 4945 4976 5011 A 5026 5064 5082 5090 5091 5102 5114 5121 5128 (Centaurus A) 5161 5206 5253 5266 5291 5398 5408 5419 5483 5516 Other ESO 269-57 ESO 325-4 ESO 383-76 ESO 444-46 Fourcade-Figueroa Object IC 3370 IC 4214 IC 4329A IRAS 13224−3809 J1144−4308 LEDA 677373 PKS 1144−379 PKS 1353−341 PKS 1424−418 Galaxy clusters Abell S740 Centaurus Cluster Shapley Supercluster Astronomical events GW190521 SN 185 SN 1895B (Z) SN 1972E SN 1986G J1407b SN 2019so Category

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Adapted from the Wikipedia article [B Centauri b](https://en.wikipedia.org/wiki/B_Centauri_b) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/B_Centauri_b?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.