An article published in “The Astrophysical Journal Letters” reports the detection of radio emissions from the brown dwarf cataloged as WISE J062309.94−045624.6, the smallest known in the field of radio astronomy. A team of researchers used the ASKAP, Australian Telescope Compact Array, and MeerKAT radio telescopes to obtain the measurements necessary to establish the nature of the object. Typically, a brown dwarf smaller than Jupiter doesn’t emit radio waves, making WISE J062309.94−045624.6 an interesting astronomical research target.
Brown dwarfs have been known for just over twenty years, although their existence was theorized much earlier. They’re called failed stars because their mass is not sufficient to ignite hydrogen fusion. The consequence is that they have scarce electromagnetic emissions which make it difficult to identify them when they aren’t companions of normal stars and even more to study their characteristics.
About 37 light-years from Earth, WISE J062309.94−045624.6 was discovered in 2011, one of more than 100 brown dwarfs identified during NASA’s Wide-field Infrared Survey Explorer (WISE) mission. WISE J062309.94−045624.6 belongs to the T8 spectral class and is very small given that its size was estimated between 65% and 95% of Jupiter’s.
Estimates of the mass of the brown dwarf WISE J062309.94−045624.6 are still very rough, ranging from a minimum of 4 to a maximum of 44 times Jupiter’s. However, values close to the minimum seem unlikely because they would place it in the category of planets. The boundary between the planet and the brown dwarf is estimated around 13 times Jupiter’s mass.
The temperature on the surface of brown dwarfs is much lower than the surface of a “real” star. In the case of WISE J062309.94−045624.6, it was measured at about 425° Celsius, less than a tenth of that of the surface of the Sun, which is around 5,600° Celsius.
The brown dwarf WISE J062309.94−045624.6 was studied with the Australian radio telescopes ASKAP (Australian Square Kilometer Array Pathfinder) and Australian Telescope Compact Array and with the South African MeerKAT. An ultracool brown dwarf such as WISE J062309.94−045624.6 typically doesn’t emit radio waves but the origin of those radio waves is not yet well explained. This means that this unexpected detection is interesting to try to better understand the processes taking place in these objects.
According to the models developed so far, the radio emissions from a brown dwarf are connected to their fast rotation which generates powerful magnetic fields: when those magnetic fields rotate at different speeds from the brown dwarf’s ionized atmosphere, they could create electric current flows, and a flux of electrons towards the magnetic polar region together with the rotation of the brown dwarf could produce repeated radio bursts.
The weak emissions of brown dwarfs make their study difficult and that’s why three powerful radio telescopes were used to study WISE J062309.94−045624.6 despite being in the cosmic neighborhood. The next generation radio telescope SKA will be very useful to find and study other objects of this type whose characteristics can help to better understand both gas giant planets and stars.
