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b Centauri Exoplanet System

Distant mega-Jupiter orbiting a pair of massive blue stars //

b Centauri (b Cen) is a real exoplanet system 325.2 light-years away in the constellation Centaurus. It consists of two high-mass stars—b Cen A and b Cen B—which together weigh up to 10 times that of the Sun. The primary component, b Cen A, measures a hefty 5.6 solar masses and 2.93 solar radii. It is a hot blue star of spectral type B3V, shining at several hundred times the Sun's luminosity with an 18,445 K (18,172 °C) surface temperature. The other star, b Cen B, is the smaller secondary component with an upper mass estimate of 4.4 solar masses. A distance of ~1.0 AU separate the pair, but the shape of their orbits around each other is unknown. Although such massive stars burn through their fuel rapidly and are expected to have short lifespans, b Cen is also a very young system of only 15 million years. Thus, both objects still have a plentiful supply of hydrogen and are well within the main, stable stage of their evolution.

By blocking out the stars’ glare using an instrument called a coronagraph, astronomers discovered a third body on the outskirts of b Cen in 2021. The object—designated b Cen (AB) b—is a circumbinary planet, meaning that it orbits around both central stars from afar. It is a massive gas giant of 10.9 Jupiter masses, equivalent to over 3400 Earths. Still red-hot from the residual heat of its formation, b Cen (AB) b shines with a luminosity one ten-thousandth that of the Sun. While certainly minuscule compared to the brightness of a star, it is largely thanks to this glow that the planet could be seen by our telescopes. b Cen (AB) b’s distance to its hosts is projected at a vast 556 AU. This is about 19 times that of Neptune’s and is comparable to the average distance of Sedna around the Sun. While the shape of its path is not well constrained, a single orbit is estimated to take anywhere from 2650 to 7170 years.

b Cen is one of the most massive star systems around which an exoplanet has been found, challenging the traditional belief that intense stellar winds in high-mass stars would quickly blow away any planet-forming materials before they had a chance to coalesce. b Cen (AB) b demonstrates that exoplanets can and do exist around these behemoths, but its wide orbit raises questions on how exactly it came to be. In most cases, gas giants are thought to originate by a gradual process called core accretion, where particles in a protoplanetary disk first build up into a solid core. Once this core reaches a critical mass, it rapidly and exponentially accumulates gas from its surroundings until a giant planet is born. However, if b Cen (AB) b formed at its current location over 500 AU out, there could not have been enough material for core accretion to explain such a huge planet. Instead, it might have been produced through an alternative mechanism called gravitational instability—a faster process involving the direct collapse of a region within a protoplanetary disk. However, gravitational instability tends to produce even larger objects like brown dwarfs or companion stars, so perhaps this mega-Jupiter did form closer in via core accretion before being flung out through an interaction with the stars it orbits. Overall, record-setting examples like b Cen continue to showcase the diverse shapes, sizes and history of star systems beyond our own.

Note: b Centauri is not to be confused with Beta Centauri or B Centauri, which are different star systems of similar names.

This simulation replicates the b Centauri system from real data wherever possible, though fictional elements may be incorporated due to knowledge gaps:

• Due to the difficulty of observing the secondary star b Cen B, not much else is known beyond its potential mass. I have used Universe Sandbox to approximate its properties, arriving at a 4.4-solar-mass and 2.55-solar-radii star with a surface temperature of 15,678 K (15,405 °C).
  
• The size of b Cen (AB) b is unknown, but young gas giants tend begin fairly large before shrinking over time as their heat is lost to space. Universe Sandbox models its size at 1.51 Jupiter radii, assuming it is 15 million years old with a Jupiter-like composition.
  
• The surface temperature of b Cen (AB) b is similarly unknown, but it does have a log luminosity (Lbol/Lsun) = –3.98. Inputting this value[www.omnicalculator.com] alongside the object’s size (modelled in-game, 1.51 Jupiter radii = 105,325 km) allows us to approximate its temperature at 1502 K (1229 °C).
  
• This stimulation has accurate and functional orbits, but trail mode is recommended due to display limitations of orbit mode in circumbinary systems. Lastly, b Cen (AB) b would appear to move slowly at the default simulation speed but keep in mind the long timescales at work: even at 1 year/sec, a full orbit requires over 1 h of real-life time!

* b Cen, GCRV 8538, 2MASS J14415758-3747366, uvby98 100129116, ** SHT 56A, GEN# +1.00129116, PPM 292953, WDS J14420-3748Aa,Ab, ** RIZ 12, GSC 07819-02819, ROT 2099, WDS J14420-3748A, AKARI-IRC-V1 J1441575-374736, HD 129116, SAO 205839, WEB 12379, ALS 16356, HGAM 2026, SKY# 26714, WISE J144157.55-374736.7, CD-37 9618, HIC 71865, TD1 17630, [B10] 3747, CPC 18 7136, HIP 71865, TIC 159589603, Gaia DR2 6105713692543053056, CPD-37 6185, HR 5471, TYC 7819-2819-1, Gaia DR3 6105713692544123520, EUVE J1441-37.8, IRAS 14388-3734, UBV 12793, GC 19779, JP11 2525, UBV M 20298

• Fitzpatrick, E.L. and Massa, D., 2005. Determining the physical properties of the B Stars. II. Calibration of synthetic photometry. The Astronomical Journal, 129(3), p.1642.
  
• Kratter, K., 2021. Giant planet imaged orbiting two massive stars.
  
• Janson, M., Gratton, R., Rodet, L., Vigan, A., Bonnefoy, M., Delorme, P., Mamajek, E.E., Reffert, S., Stock, L., Marleau, G.D. and Langlois, M., 2021. A wide-orbit giant planet in the high-mass b Centauri binary system. Nature, 600(7888), pp.231-234.
  
• Rizzuto, A.C., Ireland, M.J., Robertson, J.G., Kok, Y., Tuthill, P.G., Warrington, B.A., Haubois, X., Tango, W.J., Norris, B., ten Brummelaar, T. and Kraus, A.L., 2013. Long-baseline interferometric multiplicity survey of the Sco–Cen OB association. Monthly Notices of the Royal Astronomical Society, 436(2), pp.1694-1707.
  
• Wolff, S.C., Strom, S.E. and Dror, D., 2007. Rotational Velocities For B0-B3 Stars in 7 Young Clusters: Further Study of the Relationship between Rotation Speed and Density in Star-Forming Regions. arXiv preprint astro-ph/0702133.