Astronomers find a weird object on the boundary of an exoplanet and a star

(S. Hinkley et al. / arXiv, 2023 https://bit.ly/3JiNFnQ)

Astronomers led by Sasha Hinkley of the University of Exeter have discovered a massive exoplanet that falls into the transition region between exogiants and brown dwarfs.

Using the Gaia Space Telescope and ground-based telescopes the team found that deuterium fusion reactions can take place in the core of the planet HD 206893c.

The question of how giant exoplanets and brown dwarfs differ from each other is still a matter of controversy among planetary scientists.

According to astronomers, if a body has a mass less than 13 Jupiter masses, it can be considered a planet.

Also, the limit at which deuterium nuclear combustion reactions can begin to occur in the core of an object.

Astronomers look for systems where there are both exoplanets and brown dwarfs that formed at the same time from the same protoplanetary disk.

The intention is to test theories of the formation of such objects and understand the difference between them.

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THE DISCOVERY
Hinkley's team announced the discovery of the exoplanet HD 206893c in a sun-like star system located 130 light-years from the Sun.

The discovery was made thanks to astrometric data obtained by the Gaia space telescope.

The team also used data on the radial velocity fluctuations of the star obtained by the HARPS and GRAVITY spectrographs installed on the telescopes of the ESO.

HD 206893 is an F5V star with approximately solar metallicity and a mass of 1.24 solar masses.

Most estimates of the age of this star are in the range of 100–300 million years, but some papers allow an age of up to 3 or 50 million years, or 1.1 billion years.

In 2017, a companion HD 206893B was discovered around the star, the semi-major axis of the orbit of which is 9.6 astronomical units, and the eccentricity is 0.14.

The object has a mass of 28 Jupiter masses and a radius of 1.25 Jupiter radii, which makes it a brown dwarf.

HD 206893c has a mass of 12.7 Jupiter masses and a radius of 1.46 Jupiter radii, placing this exoplanet in the transition region between brown dwarfs and exogiants.

The luminosity of HD 206893c can be explained by models that include deuterium nuclear combustion in the object's core and a cloudy atmosphere.

At the same time, scientists were able to unambiguously determine the age of the system, which is now 155 ± 15 million years.

Observations of HD 206893 will continue, as it is an extremely valuable object, allowing to test models for the formation of exogiants and brown dwarfs.

Also, astronomers intend to clarify the nature of HD 206893c.

Sources:

• arXiv.org: https://arxiv.org/abs/2208.04867
• Exeter University: https://www.exeter.ac.uk/news/homepage/title_955572_en.html
• Space.com: https://www.space.com/europe-gaia-mission-exoplanet-nuclear-fusion

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