Until now, some scientists believed planets could not exist around stars this big and intense.

The Very Large Telescope (VLT) of the European Southern Observatory (ESO) has caught a snapshot of a planet orbiting b Centauri, a two-star system visible to the naked eye.

This is the hottest and most massive planet-hosting star system discovered to date, with a planet orbiting it at a distance 100 times that of Jupiter’s orbit around the Sun. Until today, some scientists believed that planets could not exist around stars this large and intense.

“Finding a planet around b Centauri was very exciting since it completely changes the picture about massive stars as planet hosts,” explained first author and astronomer Markus Janson.

The b Centauri two-star system (also known as HIP 71865), located around 325 light-years away in the constellation Centaurus, has at least six times the mass of the Sun, making it by far the most massive system around which a planet has been proven. Until recently, no planets have been discovered orbiting a star more than three times the mass of the Sun.

Most large stars are also incredibly hot, and this system is no exception: its main star is a B-type star that is more than three times as hot as the Sun. Because of its high temperature, it emits a lot of ultraviolet and X-ray radiation.  

This sort of star’s huge mass and heat have a considerable impact on the surrounding gas, which should work against planet formation. The hotter a star gets, the more high-energy radiation it emits, causing the surrounding material to evaporate quicker.

“B-type stars are generally considered as quite destructive and dangerous environments, so it was believed that it should be exceedingly difficult to form large planets around them,” Janson said.

However, the recent discovery demonstrates that planets can develop in such harsh star systems.

“The planet in 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,” added co-author Gayathri Viswanath.

“It’s a harsh environment, dominated by extreme radiation, where everything is on a gigantic scale: the stars are bigger, the planet is bigger, the distances are bigger.”

Indeed, the discovered planet, known as b Centauri (AB)b or b Centauri b, is likewise extreme. It is ten times the size of Jupiter, making it one of the most massive planets ever discovered. Furthermore, it swings around the solar system in one of the most expansive orbits yet discovered, at a distance 100 times bigger than Jupiter’s distance from the Sun. This great separation from the center pair of stars may be critical to the planet’s survival.

The powerful Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE) located on ESO’s VLT in Chile enabled these findings. SPHERE has already imaged planets orbiting stars other than the Sun, including the first image of two planets around a Sun-like star.

SPHERE was not, however, the first instrument to scan this planet. The scientists dug into archive data on the b Centauri system as part of their research and discovered that the planet had been observed more than 20 years ago by the ESO 3.6-m telescope, however it was not recognized as a planet at the time.

Source: 10.1038/s41586-021-04124-8 

Image Credit: ESO

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