SPHERE Directly Images Wide-Orbit Gas Giant in Nearby Binary System

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Named b Centauri (AB)b (or b Centauri b), the newfound exoplanet is estimated to be only 15 million years old and 10 times the mass of Jupiter, according to an analysis of data collected by the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s Very Large Telescope (VLT).

An artist’s impression of b Centauri b and its host stars. Image credit: ESO / L. Calçada.

The b Centauri system is located approximately 318 light-years away in the constellation of Centaurus.

Also known as b Cen (but not β Cen), HR 5471 or HIP 71865, it consists of a close pair of stars.

The more massive star is named b Cen A and has a type of B2.5, corresponding to an effective temperature of approximately 18,000 K. The properties of the second star, b Cen B, are uncertain.

The system is roughly 15 million years old, and likely belongs to the Upper Centaurus Lupus association of stars.

“Most massive stars are also very hot, and this system is no exception: its main star is a so-called B-type star that is over three times as hot as the Sun,” said Stockholm University astronomer Dr. Markus Janson and his colleagues.

“Owing to its intense temperature, it emits large amounts of ultraviolet and X-ray radiation.”

“The large mass and the heat from this type of star have a strong impact on the surrounding gas, that should work against planet formation. In particular, the hotter a star is, the more high-energy radiation it produces, which causes the surrounding material to evaporate faster.”

This SPHERE image shows the most massive planet-hosting star pair to date, b Centauri, and its giant planet b Centauri b. Image credit: ESO / Janson et al.

This SPHERE image shows the most massive planet-hosting star pair to date, b Centauri, and its giant planet b Centauri b. Image credit: ESO / Janson et al.

The astronomers observed the system with VLT’s SPHERE instrument in 2019 and 2021 as part of the B-star Exoplanet Abundance Study (BEAST).

They also looked into archival data and discovered that the b Centauri b planet had actually been imaged more than 20 years ago by ESO’s 3.6-m telescope, though it was not recognized as a planet at the time.

“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,” said Gayathri Viswanath, a Ph.D. student at Stockholm University..

“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.”

b Centauri b is 10 times as massive as Jupiter, making it one of the most massive planets ever found.

Moreover, it orbits the parent stars at a distance of 560 AU (100 times greater than the distance of Jupiter from the Sun) — one of the widest orbits yet discovered.

“This large distance from the central pair of stars could be key to the planet’s survival,” the researchers said.

The team’s paper was published this week in the journal Nature.

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M. Janson et al. 2021. A wide-orbit giant planet in the high-mass b Centauri binary system. Nature 600, 231-234; doi: 10.1038/s41586-021-04124-8

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