Instead, after nine hours of seeing nothing, a flare flashed brightly, then faded out over the next two hours. The flare, very similar to the flares on our Sun, is the first ever observed on a brown dwarf. Basri and his collaborators originally planned the long observation by Chandra to eliminate the possibility that older brown dwarfs like this have hot coronae. Work by Basri and his graduate student, Subu Mohanty, has suggested that brown dwarfs lose their hot coronae as they cool below about 2,200 degrees Celsius. A paper describing the observations has been accepted by Astrophysical Journal Letters and will be published July 21.
Brown dwarfs are failed stars somewhere in mass between a large planet and a small star.
This makes them large enough to collapse and heat up, but not big enough to ignite the steady nuclear fires necessary to keep stars burning for billions of years. Instead, after a brief hot flash, brown dwarfs cool off until they become dead cinders. They are extremely dim and went undetected until the recent construction of larger, more sensitive telescopes. Basri confirmed the first lithium brown dwarf in 1995 using Hawaii's Keck I Telescope, and since then several dozen have been found in nearby clusters or floating freely in the solar neighborhood. The brown dwarf known as LP 944-20 is one of the nearest, only16 light years from Earth.