New Delhi: Astronomers from the Physical Research Laboratory in Ahmedabad have discovered a high-mass brown dwarf orbiting a mature, metal-rich G-type
star, about 293 parsecs from the Earth. The brown dwarf transits its host star from the vantage point of the Earth. The object was initially flagged as an exoplanet candidate by NASA’s Transiting Exoplanet Survey Satellite (TESS), the substellar nature of the companion was confirmed using high-precision radial velocity measurements from the ground-based PARAS-2 and TRES spectrographs. The newly characterised object, designated as TOI07154 b, contains as much mass as 71.7 Jupiters.
The mass of the brown dwarf dwarf places it precisely near the hydrogen-burning boundary that separates heavy brown dwarfs from the lowest-mass stars. Brown dwarfs form from dense knots of gas and dust, just like stars, but are not able to accumulate enough material to sustain nuclear fusion. The object is highly compact, and despite containing 71.1 times the mass of Jupiter, it is smaller than Jupiter, with a remarkable high mean density of 157 grams per cubi centimetre. It completes a close-in orbit every 8.86 days at an average distance of about 0.084 astronomical units, or 12.6 million kilometres from its host.
Brown dwarfs rare in tight orbits around Sun-like stars
The discovery is significant because brown-dwarfs are exceptionally rare in tight orbits around Sun-like stars, a demographic scarcity known as the brown dwarf desert. The brown dwarf maintains an orbital eccentricity, and because the system is older than four billion years, tidal interactions should have circularised its orbit over time. Tidal evolution simulations reveal that the survival of this eccentricity strongly indicates a stellar-like birth via molecular cloud or disk fragmentation, ruling out traditional planet-like core accretion followed by migration across the circumstellar disk, which dampens the orbital eccentricity. The object shows no radius inflation from stellar radiation, and serves as an empirical reference point for testing theories of electron-degeneracy pressure and stellar contraction.
