天文学：ケンタウルス座b星連星系を周回する未知の巨大ガス惑星が観測された

A gas-giant planet observed in a wide orbit around the high-mass star system of b Centauri A and B (b Cen AB), is reported in a paper published this week in Nature. The findings demonstrate that planets can reside in much larger stellar systems than previous research has suggested, and may improve our understanding of the planet formation process.

Confirmed observations of planets orbiting stars have indicated gas giants around stars exceeding 3 solar masses may be rare or non-existent. This notion of planet formation is challenged by b Cen AB, which resides in the Milky Way and the stars have a combined mass of between six and ten times that of our Sun.

Markus Janson and colleagues observed the planet, which they call b Cen (AB)b, between March 2019 and April 2021 using the SPHERE exoplanet imager, which is installed on the European Southern Observatory's Very Large Telescope in Paranal, Chile. They found that b Cen (AB)b orbits the stars of the binary system at 560 times the distance between Earth and the Sun. Using measurements of b Cen (AB)b’s brightness, the authors calculated that the ratio between the masses of the planet and the star system it orbits to be similar to the ratio between Jupiter and the Sun. However, b Cen (AB)b is 11 times the mass of Jupiter and its orbit is 100 times wider. Based on its location and orbit, the authors determined that b Cen (AB)b probably formed rapidly close to its present location from a dense clump that accumulated within a disc of matter that used to orbit b Cen AB.