Scientists have identified an unusually large exoplanet that orbits ab Centauri, a huge two-star system visible to the naked eye. With a combined weight of around 10 suns, it is now the heaviest star system known to host a planet.
Let’s get right to the heart of this discovery, the details of which have been published today in Nature. The newly discovered planet, named “b Cen (AB) b”, is likely a gas giant and weighs more than 10 Jupiters together, making it one of the most massive planets ever discovered. It orbits the binary system b Centauri, which is 325 light years from Earth and has a combined mass of almost 10 suns. At 52 billion miles from its host stars, this planet has one of the largest orbits ever recorded. By comparison, Pluto orbits the Sun at about 3.3 billion miles, so yeah, it’s an incredible separation.
So far, no planets have been found orbiting star systems weighing more than three solar masses. Astronomers did not believe that planets could form around systems like this, so it is forcing a major rethinking of what is possible in terms of planetary architectures and the conditions under which planets can form. Markus Janson, an astronomer at Stockholm University and first author of the study, said that what excites him most about this discovery is the “astonishing diversity” of exoplanetary systems.
“It seems that no matter where we look, around small or large stars, individual stars or binary stars, living stars or the remnants of dead stars, we always find planets of some form, even in places we did not think possible.” he wrote in an email.
That there is a planet in this star system is truly amazing. Young stars are surrounded by protoplanetary disks, from which planets eventually emerge. A hot star system like b Centauri, however, should not favor planetary formation, due to the huge amounts of ultraviolet and X-ray radiation. This high-energy radiation “tends to destroy disks in a very short time” and yes. I thought this would not give the planets enough time to form on the disk before it disappeared, ”said Janson. Yet it is there: a full-fledged planet around the Centauri b system.
Janson and his colleagues detected b Cen (AB) b with the SPHERE exoplanet imager at the European Southern Observatory’s Very Large Telescope in Chile on March 20, 2019, and then again on April 10, 2021. Astronomers used a High-contrast imaging technique for detecting the planet, in which they distinguished the dim light from the planet from the very bright light from the star system itself.
A deformable mirror in SPHERE that can rapidly change shape countered the blurring effects caused by Earth’s atmosphere, while a chronograph blocked excess light from the source target. A special technique known as Angular Differential Imaging excluded extraneous optical effects. Interestingly, follow-up work showed that the planet was observed 20 years ago by a different ESO instrument, but was not correctly identified at the time.