Massive Brown Dwarf with Unusual Orbit Revealed

An international group of astronomers has uncovered a new brown dwarf named TOI-2490 b. This celestial object is approximately 74 times the mass of Jupiter and follows a highly eccentric orbit around a sun-like star. The discovery was detailed in a paper published on August 8 on the pre-print server arXiv.

Brown dwarfs are intermediate objects with masses between those of planets and stars, ranging from 13 to 80 Jupiter masses (0.012 to 0.076 solar masses). Although numerous brown dwarfs have been identified, finding one orbiting another star is a rare event.

The research team, led by Beth A. Henderson from the University of Leicester, detected a transit signal using the TESS space telescope in the light curve of TOI-2490, a G-type main sequence star located about 872.5 light years away. Confirmatory observations verified that the signal was indeed from a brown dwarf.

According to their findings, TOI-2490 b has a size comparable to Jupiter but boasts a mass roughly 73.6 times greater, resulting in a density of 91.6 g/cm³. It completes an orbit around its host star every 60.33 days at a distance of approximately 0.31 AU, with an equilibrium temperature estimated at 464.2 K.

TOI-2490 b stands out due to its exceptionally high orbital eccentricity of about 0.78, making it the most eccentric brown dwarf observed in what is known as the BD desert—an area where such objects are rare around main sequence stars within roughly 3 AU.

The study suggests that TOI-2490 b likely formed with this high eccentricity and probably shares similar metallicity and age with its host star. The researchers also noted significant variations in the irradiation temperature of TOI-2490 b, ranging from 545 to 1,552 K as it orbits its star.

Regarding the host star, TOI-2490, it is comparable in mass to the sun and has a radius about 1.1 times that of the sun. It is estimated to be 7.9 billion years old, with a metallicity of 0.32 dex and an effective temperature of 5,558 K.