{{Short description|Binary star in the constellation Centaurus}} {{hatnote group| {{about|b Centauri|B Centauri|HD 102964|β Centauri|Beta Centauri}} {{confused|Alpha Centauri b (disambiguation){{!}}Alpha Centauri b}} }} {{Starbox begin | name = b Centauri }} {{Starbox image | image = {{Location mark |image=Centaurus constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=HD 129116 |x=210|y=370 }} | caption = Location of b Centauri (circled in red) }} {{Starbox observe | epoch = J2000.0 | constell = [[Centaurus]]<ref name=Anderson2012/> | ra = {{RA|14|41|57.59068}}<ref name=vanLeeuwen2007/> | dec = {{DEC|−37|47|36.5940}}<ref name=vanLeeuwen2007/> | appmag_v = +4.01<ref name=Anderson2012/> }} {{Starbox character | type = Main sequence | class = B3V<ref name=Hiltner1969/> | b-v = {{Val|−0.157|0.002}}<ref name=Anderson2012/> | u-b = | variable = Constant<ref name=Paunzen2017/> }} {{Starbox astrometry | radial_v = {{Val|+2.6|1.5}}<ref name=Anderson2012/> | prop_mo_ra = {{Val|-29.828|0.369}}<ref name=EDR3/> | prop_mo_dec = {{Val|-31.914|0.518}}<ref name=EDR3/> | parallax = 10.0339 | p_error = 0.3143 | parallax_footnote = <ref name=EDR3/> | dist_ly = | dist_pc = | absmag_v = −1.07<ref name=Anderson2012/> }} {{Starbox detail | mass = 5–6<ref name=Janson2021/> | radius = {{Val|2.93|0.12}}<ref name=Fitzpatrick2005/> | luminosity = 637.01<ref name=Anderson2012/> | temperature = {{Val|18310|320|fmt=commas}}<ref name=Janson2021/> | metal_fe = | gravity = {{Val|4.23|0.03}}<ref name=Fitzpatrick2005/> | rotational_velocity = 129<ref name=Wolff2007/> | age_myr = {{Val|15|2}}<ref name=Janson2021/> }} {{Starbox catalog | names = {{odlist | B=b Cen | CD=−37°9618 | FK5=2985 | HD=129116 | HIP=71865 | HR=5471 | SAO=205839 | GC=19779 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = HD+129116 }} {{Starbox end}} '''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.<ref name=Anderson2012/> It is located at a distance of approximately 325 [[light year]]s (100 [[parsec]]s)<ref name=EDR3/> from the [[Sun]] based on [[stellar parallax|parallax]], and has an [[absolute magnitude]] of −1.07.<ref name=Anderson2012/>
The primary star is a hot type-B star with a [[spectral type]] of B3V and a mass of 5 to 6 times the [[solar mass]]. The secondary star is a close companion separated by approximately 1 [[astronomical unit|AU]], with up to 4.4 times the solar mass. In 2021, a massive [[exoplanet]] was discovered by [[direct imaging]] orbiting the pair of stars (a [[circumbinary planet]]) at a distance of about 560 AU.<ref name=Janson2021/>
== Star system == This is a young stellar system, belonging to the Upper Centaurus–Lupus subgroup of the [[Scorpius–Centaurus association]], the nearest [[OB association]] to the Sun. This is an association of stars with common origin and movement.<ref name="deZeeuw1999" /> The region inside Upper Centaurus–Lupus where b Centauri is located seems to have a uniform age of 15 million years, which is therefore the age of this system (with an uncertainty of about 2 million years).<ref name="Janson2021" /> From its [[stellar parallax]] measured by the [[Gaia (spacecraft)|Gaia]] spacecraft, b Centauri is located at a distance of 325 [[light year]]s (100 [[parsec]]s).<ref name="EDR3" /> It has been noted that the secondary star may interfere with the parallax measurements, so this distance value may not be completely accurate. In any case, b Centauri seems to be located on the closer side of the Scorpius–Centaurus association, as seen from Earth, which is also indicated by its higher [[proper motion]] compared to the mean of the association.<ref name="Janson2021" />
The primary star is a [[B-type main-sequence star]] with a [[stellar classification]] of B3V,<ref name="Hiltner1969" /> which indicates it is engaged in [[stellar core|core]] [[hydrogen fusion]] to generate energy. The object has been used as a "standard star" in several [[Photometry (astronomy)|photometric systems]], and it appears to be non-[[variable star|variable]].<ref name="Paunzen2017" /> It has a high rate of spin, showing a [[projected rotational velocity]] of 129 km/s.<ref name="Wolff2007" /> The star has 5 to 6<ref name="Janson2021" /> times the [[mass of the Sun]] and 2.9<ref name="Fitzpatrick2005" /> times the [[Sun's radius]]. It is radiating 637<ref name="Anderson2012" /> times the [[luminosity of the Sun]] from its [[photosphere]] at an [[effective temperature]] of 18,445 K.<ref name="Fitzpatrick2005" />
In 1968 the primary was found to have variable [[radial velocity]], which is evidence of a second star in the system, but no orbit was published.<ref name="Gutierrez-Moreno1968" /> The existence of the secondary star was confirmed in 2010 with an [[interferometry|interferometric]] observation, which revealed it at a separation of {{val|9.22|ul=mas}}, or {{val|1.0|ul=AU}} at the system's distance.<ref name="Rizzuto2013" /> The difference in magnitude between the stars is 1.06,<ref name="Rizzuto2013" /> from which a mass of {{solar mass|4.4}} is calculated for the secondary. However this value for the magnitude difference is uncertain, since it was based on a single observation and the detection is close to the instrument performance limit, the mass of {{solar mass|4.4}} is considered an upper estimate.<ref name="Janson2021" /> Given all uncertainties, the total mass of the system is estimated at 6 to {{solar mass|10}}.<ref name="Janson2021" />
==Planetary system==
[[File:Artist impression showing b Centauri and its giant planet.jpg|thumb|left|Artist's impression showing b Centauri and its giant planet b Centauri b.]][[File:Eso2118b.jpg|thumb|left|250px|b Centauri imaged by [[Very Large Telescope|VLT]]/[[Spectro-Polarimetric High-Contrast Exoplanet Research|SPHERE]]. The planet b Centauri b is indicated by an arrow. '''Credit''': ''ESO/Janson et al.'']]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 [[direct imaging|directly imaged]].<ref name=Janson2021beast/> The first observation of the system in 2019 revealed an object at a {{val|5.3|u=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.<ref name=Janson2021/> 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.<ref name=Janson2021/><ref name=Shatsky2002/> With a primary star mass of {{solar mass|5–6}} and a total system mass of {{solar mass|6–10}}, b Centauri is the most massive system around which a planet has been found; previously, the most massive star with a known planet was {{solar mass|3}}. The discovery was published in December 2021 on the scientific journal ''[[Nature (journal)|Nature]]'' and was led by [[Stockholm University]] astronomer Markus Janson.<ref name=Janson2021/> 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 {{val|560|u=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 [[Orbital eccentricity|eccentricity]] smaller than 0.4.<ref name=Janson2021/>
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.<ref name=Janson2021/>
The formation mechanism for b Cen (AB)b is uncertain. It is believed that most giant planets are formed via [[Core-accretion theory|core accretion]], in which a rocky core, after growing to a critical mass, starts rapidly [[Accretion (astrophysics)|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.<ref name=Janson2021/>
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 {{solar mass}} and reaches almost zero for 3 {{solar mass}} 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 [[Planetary migration|migrating]] closer to their stars, but allows the existence of distant planets like b Cen (AB)b.<ref name=Janson2021/>
{{OrbitboxPlanet begin | name = b Centauri | period_unit = year | table_ref = <ref name=Janson2021/> }} {{OrbitboxPlanet | exoplanet = [[b Centauri b|(AB)b]] | mass = {{val|10.9|1.6}} | semimajor = {{val|556|17}} | period = {{val|7170|2650}} | eccentricity = 0.4 | inclination = {{val|157|128|ul=deg}} | radius ={{val|1.11}} }} {{Orbitbox end}}
==References== <references> <ref name=EDR3>{{cite Gaia EDR3|6105713692544123520}}</ref>
<ref name=SIMBAD>{{cite simbad | title=b Cen | access-date=2020-03-05}}</ref>
<ref name=vanLeeuwen2007>{{cite journal | first=F. | last=van Leeuwen | date=November 2007 | title=Validation of the new Hipparcos reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | arxiv=0708.1752 | s2cid=18759600 }}</ref>
<ref name=Anderson2012>{{cite XHIP|71865}}</ref>
<ref name=Fitzpatrick2005>{{cite journal | last1=Fitzpatrick | first1=E. L. | last2=Massa | first2=D. | title=Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry | journal=The Astronomical Journal | volume=129 | issue=3 | pages=1642–1662 |date=March 2005 | doi=10.1086/427855 | arxiv=astro-ph/0412542 | bibcode=2005AJ....129.1642F | s2cid=119512018 }}</ref>
<ref name=Hiltner1969>{{cite journal | display-authors=1 | last1=Hiltner | first1=W. A. | last2=Garrison | first2=R. F. | last3=Schild | first3=R. E. | title=MK Spectral Types for Bright Southern OB Stars | journal=Astrophysical Journal | volume=157 | pages=313–326 | date=July 1969 | doi=10.1086/150069 | bibcode=1969ApJ...157..313H | doi-access=free }}</ref>
<ref name=Wolff2007>{{cite journal | last1=Wolff | first1=S. C. | last2=Strom | first2=S. E. | last3=Dror | first3=D. | last4=Venn | first4=K. | title=Rotational Velocities for B0-B3 Stars in Seven Young Clusters: Further Study of the Relationship between Rotation Speed and Density in Star-Forming Regions | journal=[[The Astronomical Journal]] | volume=133 | pages=1092–1103 | date=2007 | issue=3 | doi=10.1086/511002 | bibcode=2007AJ....133.1092W | arxiv=astro-ph/0702133 | s2cid=119074863 }}</ref>
<ref name=Paunzen2017>{{cite journal |bibcode=2017sbcs.conf..180P |title=BRITE photometry of seven B-type stars |last1=Paunzen |first1=E. |last2=Rode-Paunzen |first2=M. |journal=Second Brite-Constellation Science Conference: Small Satellites – Big Science |volume=5 |pages=180 |year=2017 |arxiv=1612.04714 }} </ref>
<ref name=Janson2021>{{cite journal |bibcode=2021Natur.600..231J|title=A wide-orbit giant planet in the high-mass b Centauri binary system|last1=Janson|first1=Markus|last2=Gratton|first2=Raffaele|last3=Rodet|first3=Laetitia|last4=Vigan|first4=Arthur|last5=Bonnefoy|first5=Mickaël|last6=Delorme|first6=Philippe|last7=Mamajek|first7=Eric E.|last8=Reffert|first8=Sabine|last9=Stock|first9=Lukas|last10=Marleau|first10=Gabriel-Dominique|last11=Langlois|first11=Maud|last12=Chauvin|first12=Gaël|last13=Desidera|first13=Silvano|last14=Ringqvist|first14=Simon|last15=Mayer|first15=Lucio|last16=Viswanath|first16=Gayathri|last17=Squicciarini|first17=Vito|last18=Meyer|first18=Michael R.|last19=Samland|first19=Matthias|last20=Petrus|first20=Simon|last21=Helled|first21=Ravit|last22=Kenworthy|first22=Matthew A.|last23=Quanz|first23=Sascha P.|last24=Biller|first24=Beth|last25=Henning|first25=Thomas|last26=Mesa|first26=Dino|last27=Engler|first27=Natalia|last28=Carson|first28=Joseph C.|journal=Nature|year=2021|volume=600|issue=7888|pages=231–234|doi=10.1038/s41586-021-04124-8|pmid=34880428|arxiv=2112.04833|s2cid=245005994}}</ref>
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<ref name=Gutierrez-Moreno1968>{{Cite journal|bibcode = 1968ApJS...15..459G|title = A Photometric Investigation of the SCORPIUS-CENTAURUS Association|last1 = Gutierrez-Moreno|first1 = Adelina|last2 = Moreno|first2 = Hugo|journal = The Astrophysical Journal Supplement Series|year = 1968|volume = 15|page = 459|doi = 10.1086/190168|doi-access = free}}</ref>
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<ref name=Janson2021beast>{{Cite journal|bibcode = 2021A&A...646A.164J|title = BEAST begins: Sample characteristics and survey performance of the B-star Exoplanet Abundance Study|last1 = Janson|first1 = Markus|last2 = Squicciarini|first2 = Vito|last3 = Delorme|first3 = Philippe|last4 = Gratton|first4 = Raffaele|last5 = Bonnefoy|first5 = Mickaël|last6 = Reffert|first6 = Sabine|last7 = Mamajek|first7 = Eric E.|last8 = Eriksson|first8 = Simon C.|last9 = Vigan|first9 = Arthur|last10 = Langlois|first10 = Maud|last11 = Engler|first11 = Natalia|last12 = Chauvin|first12 = Gaël|last13 = Desidera|first13 = Silvano|last14 = Mayer|first14 = Lucio|last15 = Marleau|first15 = Gabriel-Dominique|last16 = Bohn|first16 = Alexander J.|last17 = Samland|first17 = Matthias|last18 = Meyer|first18 = Michael|last19 = d'Orazi|first19 = Valentina|last20 = Henning|first20 = Thomas|last21 = Quanz|first21 = Sascha|last22 = Kenworthy|first22 = Matthew|last23 = Carson|first23 = Joseph C.|journal = Astronomy and Astrophysics|year = 2021|volume = 646|pages = A164|doi = 10.1051/0004-6361/202039683|arxiv = 2101.02043|s2cid = 230770142}}</ref>
<ref name=Shatsky2002>{{Cite journal|bibcode = 2002A&A...382...92S|title = The mass ratio distribution of B-type visual binaries in the Sco OB2 association|last1 = Shatsky|first1 = N.|last2 = Tokovinin|first2 = A.|journal = Astronomy and Astrophysics|year = 2002|volume = 382|page = 92|doi = 10.1051/0004-6361:20011542|arxiv = astro-ph/0109456|s2cid = 16697655}}</ref> </references>
==External links==
*{{cite web | title = ESO telescope images planet around most massive star pair to date | url = https://www.eso.org/public/news/eso2118/ | publisher = [[European Southern Observatory]] | date = 8 December 2021 | access-date = 8 December 2021}}
{{Stars of Centaurus}}
[[Category:B-type main-sequence stars]] [[Category:Bayer objects|Centauri, b]] [[Category:Centaurus]] [[Category:Durchmusterung objects|CD-37 09618]] [[Category:Henry Draper Catalogue objects|129116]] [[Category:Hipparcos objects|071865]] [[Category:Bright Star Catalogue objects|5471]] [[Category:Binary stars]] [[Category:Planetary systems with one confirmed planet]]