An international team of scientists has identified five objects with mass near the boundary separating stars and brown dwarfs. According to the researchers, this will allow us to understand the nature of these mysterious objects, which themselves occupy an intermediate position between massive gas giants and low-mass stars. This is reported in an article published in the journal Astronomy & Astrophysics.
Like Jupiter and other gas giant planets, stars are mostly composed of hydrogen and helium. Unlike planets, stars are so massive that hydrogen atoms begin to fuse to form helium, releasing enormous amounts of energy and light. However, brown dwarfs are not massive enough to effectively support nuclear fusion reactions, and therefore cannot emit light and energy like stars. They are known to be capable of producing small amounts of the heavy hydrogen isotope, deuterium, but the light produced by this process is much dimmer.
New brown dwarfs were found using the TESS space telescope, which searches for exoplanets by the transit method, that is, it monitors the passage of large objects against the background of the disk of stars. Five celestial bodies have been identified: TOI-148, TOI-587, TOI-681, TOI-746 and TOI-1213, which revolve around their parent stars with a period of 5-27 days. They have a radius of 0.81 to 1.66 times that of Jupiter, and 77-98 times more massive. This puts them on the border between brown dwarfs and stars.
Brown dwarfs should shrink over time as they burn up their deuterium stores and cool down. It turned out that the two oldest objects, TOI 148 and 746, have a smaller radius, while the two younger dwarfs have a larger radius. However, astronomers are still not sure if they are not low-mass stars, and cannot draw definitive conclusions about the nature of the objects.