"This object is the coolest brown dwarf ever detected emitting radio waves - it's half the temperature of the previous record holder, making it only about five times hotter than Jupiter," said graduate student Matthew Route, the lead author of the discovery paper. The surface temperature of J1047+21 is approximately 630 degrees Celsius (1,160 Fahrenheit).
Other brown dwarfs have been discovered emitting infrared radiation at cooler surface temperatures - down to a record-breaking 25 degrees Celsius (80 Fahrenheit) in the case of a Y-class ultra-cool brown dwarf called "WISE 1828+2650," 30 light-years from Earth. But J1047+21 is the coolest "radio-star" detected to date.
But how radio waves are generated by a lone brown dwarf is a puzzle unto itself. The emissions "must be generated by electrons spiraling along the magnetic field," Alex Wolszczan, project leader of this study, told Discovery News. "The real puzzle is how do you generate plasma in such a cool environment?"
Primarily, there needs to be a magnetic field surrounding the brown dwarf, not dissimilar to the magnetosphere that surrounds our planet. But to generate radio waves, electrons need to be supplied to the magnetic field - as they are negatively charged, the magnetic field causes them to spiral. It's the motion of electrons that generates the radio waves detected by Arecibo.