Astronomers using direct observation have discovered a giant planet with multiple and wide orbits. It is located in a binary star system with a massive pair of stars at a distance of 560 times the distance between the Earth and the Sun. This discovery confirms that exoplanets can exist in much more massive star systems than previously thought.
Is there a connection between exoplanets and their stars?
One of the interesting problems in exoplanetology is to establish a connection between the mass of a parent star and the properties of exoplanets orbiting around it. In particular, scientists know that giant planets are more often found in close orbits around stars with a mass of up to 1.9 solar masses; above this value, the frequency of the appearance of such bodies decreases rapidly.
This may mean that the processes of planet formation are worse in more massive stars, and giant planets around stars with masses of more than three solar masses may be a rare phenomenon or practically absent. This is attributed, in particular, to the powerful fluxes of radiation from the star, which can evaporate the surrounding matter of the circumstellar disk.
A giant planet discovered in the most massive star system
A group of astronomers led by Markus Janson of Stockholm University announced the discovery of the giant planet b Cen (AB) b in the massive close binary star system b Centauri, located 305 light-years from the Sun. The observations were carried out from March 2019 to April 2021 using the SPHERE receiver installed at the VLT telescope complex in Chile as part of the BEAST program (B-star Exoplanet Abundance Study).
The system consists of stars with a total mass of 6-10 solar masses. The more massive star is designated b Centauri A and has a spectral type B2.5V, which corresponds to an effective temperature of about 18 thousand kelvin, the properties of the second star have not yet been determined. Planet b Centauri (AB) b was classified as a super-Jupiter; it revolves around both stars at once, which makes it a planet with multiple orbits.
Characteristics of the exoplanet
The exoplanet has a mass of about 10.9 times that of Jupiter and is estimated to be 15 million years old. Its distinctive feature is its orbit – with a planet-to-star mass ratio of 0.10–0.17 percent (which is similar to the ratio for Jupiter and the Sun), the distance between an exoplanet and a pair of stars is about a hundred times greater than that from Jupiter to the Sun.
The researchers believe that such a giant planet is unlikely to have formed in the current orbit due to the mechanism of accretion of matter from the protoplanetary disk onto the core. Most likely, the exoplanet formed in another region of the system, and then migrated to its current orbit, or was formed due to the mechanism of gravitational instability of the circumstellar disk. Another important conclusion is that stars and stellar systems with a mass of at least 6-10 solar masses can indeed have giant exoplanets in wide orbits.
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• ESO. (n.d.). ESO telescope images planet around most massive star pair to date.
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• Rabie, P. (2021, December 8). Look: Scientists just discovered a gigantic planet that shouldn’t exist. Inverse.
• Starr, M. (n.d.). ‘alien world’ found in giant star system challenges our thinking on planet formation. ScienceAlert.
• Wall, M. (2021, December 8). Record-breaking alien planet spotted circling massive, Superhot Star Duo (photo). Space.com.
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