hd 19728

A brown dwarf is an astronomical object that is intermediate between a planet and a star. Brown dwarfs typically have a mass less than 0.075 times that of the Sun, or about 75 times that of Jupiter. Unlike stars, brown dwarfs do not sustain stable hydrogen fusion in their cores. They can, however, fuse deuterium, a rare isotope of hydrogen, during their early stages. Brown dwarfs are supported against gravitational collapse by electron degeneracy pressure, preventing them from reaching the temperatures necessary for hydrogen fusion like stars do. They are not actually brown but can appear from deep red to magenta, depending on their temperature. Over time, brown dwarfs cool and fade, with their surface temperatures ranging from about 2,800 K for the most massive and youngest to as low as 300 K for the oldest and smallest.