NASA's TESS Discovers Massive Brown Dwarf Orbiting an M-Dwarf Star

 Utilizing NASA's Transiting Exoplanet Survey Satellite (TESS), astronomers have uncovered a massive brown dwarf, nearly 80 times the mass of Jupiter, orbiting an M-dwarf star known as TOI-5375. The discovery, detailed in a paper published on April 10 on the arXiv pre-print server, is a rare find in the realm of brown dwarfs.

Brown Dwarfs: The Intermediate Objects

Brown dwarfs (BDs) are celestial bodies that fall between planets and stars, with masses ranging from 13 to 80 Jupiter masses (0.012 and 0.076 solar masses). Although numerous brown dwarfs have been identified, those orbiting other stars remain scarce.

TESS Observations and the Discovery of TOI-5375 b

A recent transit signal observed by TESS in the light curve of TOI-5375 (also known as TIC 71268730), an active M dwarf approximately 400 light years away, caught the attention of astronomers. Led by Jesus Maldonado from the Palermo Astronomical Observatory in Italy, the team determined that this signal is caused by a massive substellar object through a combination of space-based photometric observations from TESS and high-precision radial velocities from ground-based facilities.

The researchers stated, "We reveal the presence of a companion in the brown dwarf/very-low-mass star boundary orbiting around the star TOI-5375." This newly discovered companion, designated TOI-5375 b, is the size of Jupiter and possesses an estimated mass of 77 Jupiter masses, resulting in a density of 98 g/cm3. It orbits the star every 1.72 days at a distance of 0.025 AU and is believed to have an equilibrium temperature between 931 and 1,107 K.

Classifying TOI-5375 b as a Massive Brown Dwarf

Based on the derived properties, Maldonado's team classified TOI-5375 b as a massive brown dwarf. The researchers noted that the newly discovered object lies on the boundary between brown dwarfs and very-low-mass stars. The discovery of TOI-5375 b is significant for astronomers studying the brown dwarf/star boundary, as massive substellar companions orbiting M dwarfs are rarely encountered.

The Host Star: TOI-5375

The host star, TOI-5375, has a spectral type M0.5 and is about 37% smaller and less massive than the Sun. Its rotational period is approximately 1.97 days, and its effective temperature is calculated to be around 3,800 K.

The paper's authors suggest that the orbit of TOI-5375 b is decaying relatively quickly based on the star's rotational period. They assume that the system is currently in a phase where the star is nearing synchronization with the companion's orbital period.

In conclusion, the researchers recommend further observations of the system using space observatories such as the James Webb Space Telescope (JWST). These studies could enhance our understanding of the atmospheres of massive brown dwarfs and low-mass stars.