How planets are born: the answer may lie in this exoplanet

The planet b Centauri b is one of the most massive objects ever discovered and is located in the hottest system in which a planet has ever been detected

The exoplanet of record has just been discovered. A study published yesterday in the journal Nature - authored by Markus Janson, Raffaele Gratton and Joseph C. Carson - could force scientists to rethink some of the most established assumptions about planet formation.

The newly discovered planet, which may have been spotted as long as 20 years ago without making any stir in the eyes of the technology of the day, is called b Centauri b and defies all statistics.

The exoplanet of record

The planet under study has characteristics that, according to scientists, defy all logic until now accepted.

It is 11 times larger than Jupiter, and is among the heaviest celestial objects ever discovered, is located in the constellation b Centauri, a rather young binary system that is located about 325 light years from Earth. The two stars that make up the b Centauri binary system, together, have a mass between 6 and 10 times that of the Sun: this makes b Centauri the most massive star system in which a planet has ever been detected.

The b Centauri system is also the hottest ever to host a planet, as the study points out: the system's main star, b Centauri A, is a class B star, meaning it is among the brightest in the celestial vault. To understand each other, only one star in about 800 belongs to this class, also called "blue" stars: the brightest from Earth is Rigel, in the constellation of Orion.

Until now it was considered almost impossible to intercept a planet in the "vicinity" of a blue star, three times more powerful than the Sun and rather incompatible with the formation of large celestial bodies. As stated by Janson, author of the study, "B-class stars are considered quite destructive and dangerous, and it was believed that it must be extremely difficult to form large planets around them."

The newly discovered planet, however, in addition to having an unusual mass, serenely orbits a star (actually two) that has a temperature of over 18,000 °C.

New Light on Planet Formation

The Centauri b exoplanet was identified through the use of the SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) instrument, installed on the Very Large Telescope in Chile, the same one that may have already glimpsed the planet years ago.

In addition to the incredible characteristics mentioned above, b Centauri b has other aspects that could be fundamental, in the next studies of planet formation.

His orbit, for example, is among the widest ever detected - which could explain its "resistance" to the extreme heat of its star system. Currently, the planet of record is about 550 astronomical units away from the stars: about 14 times the distance between Earth and Pluto, the celestial body at the extreme periphery of the solar system.

Still unclear is how such a massive planet could have formed on such an extended orbit. As usual, there are two options: either it formed near the two stars in the system by accretion and then moved to its current orbit by gravitational interactions, or it formed near its current location involving a process known as "gravitational instability".

The gravitational instability mechanism, in fact, tends to generate very large objects, often so large that they never become planets, but rather take the form of clusters, or strands of galaxies.

As written in the paper, "our results show that planets can be found in star systems that are much more massive than might have been expected from previous studies." A new direction, both for the search for other planets and for understanding the mechanisms by which the planets in the Universe form.