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Discovered a planet in an unsuspected place

With the help of an ‘exoplanet finder’ installed at the Very Large Telescope (Chile), an international team of astronomers has directly observed a orbiting planet b Centauri . It is the hottest and most massive planet-harboring star system found to date, as reported this week in the journal Nature .

“It has been very exciting to discover a planet around b Centauri, since it completely changes the image we have of massive stars as hosts of planets,” explains Markus Janson , astronomer of Stockholm University (Sweden) and first author of the study.

Some members of the astronomical community believed that planets could not exist around such massive and hot stars as b Centauri, but one has been found orbiting this double star

Located approximately 325 light years away , in the constellation Centaurus , the two-star system b Centauri (also known as HIP 71865 and visible to the naked eye) has at least six times the mass of the Sun , making it by far the most massive system around which the presence of a planet has been confirmed.

Until now, no exoplanets have been seen around a star more than three times as massive as the Sun. In fact, some members of the astronomical community believed that they could not exist around stars as massive and hot as b Centauri.

Discovered a planet in an unsuspected place

Illustration of the discovered planet (b Centauri b) orbiting the binary system b Centauri. / ESO / L. Calçada

Most of the massive stars are also very hot , and this system is no exception: their main star is a so-called type B star , which is more than three times hotter than the Sun. Due to its intense temperature, it emits large amounts of ultraviolet radiation and X-rays.

A hostile environment for the formation of planets

The great mass and heat of these types of stars have a strong impact on the surrounding gas, which should work against the formation of planets. In particular, the hotter a star is, the more high-energy radiation produces, causing the surrounding material to evaporate faster.

“Type B stars are generally considered quite destructive and dangerous environments, so it was believed that it should be extremely difficult to form large planets around them,” says Janson. But the new discovery shows that planets can form in such hostile star systems.

The exoplanet b Centauri b is 10 times more massive than Jupiter, making it one of the most massive ever found, and orbits at a distance 100 times greater than that which separates it from the Sun

“The planet of b Centauri is an alien world in an environment that is completely different from what we experience here on Earth and in our solar system,” explains co-author, Gayathri Viswanath , PhD student at Stockholm University. “It is a hostile environment, dominated by extreme radiation, where everything is on a gigantic scale: the stars are bigger, the planet is bigger, the distances are bigger.”

The discovered planet itself, called b Centauri (AB) b or b Centauri b , is also extreme. It is 10 times more massive than Jupiter, making it one of the most massive planets ever found.

Furthermore, it moves around the star system in one of the widest orbits discovered so far, at a distance 100 times greater than that which separates Jupiter from the Sun . This great distance from the central pair of stars could be key to the survival of the planet.

SPHERE exoplanet detector

The finding was made possible thanks to the instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research, search for exoplanets with spectropolarimetry of high contrast), installed in the VLT telescope of the European Southern Observatory (ESO) in the Chilean Atacama desert.

SPHERE had already imaged several exoplanets orbiting stars other than the Sun, including the first image of two planets orbiting a Sun-like star , but it was not the first instrument to get pictures of b Centauri b. The team discovered that they had already been obtained from it more than 20 years ago with the ESO 3.6m Telescope , although it was not identified as a planet at the time.

The authors hope that ESO’s future Extremely Large Telescope (ELT), which will begin observations later this decade, will provide new data on this and many other exoplanets.


Markus Janson et al. “A wide-orbit giant planet in the high-mass b Centauri binary system.” Nature , 2021.

Rights: Creative Commons.



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