2MASS J10475385+2124234

2MASS J10475385+2124234 (abbreviated to 2MASS J1047+21) is a brown dwarf of spectral class T6.5, in the constellation Leo. This object lies at a distance of 34 light-years from Earth. It first attracted attention by becoming the first brown dwarf of spectral class T from which radio waves were detected. This discovery then permitted its wind speeds to be computed.

Discovery

2MASS J1047+21 was discovered in 1999 along with eight other brown dwarf candidates during the Two Micron All-Sky Survey (2MASS), conducted from 1997 to 2001. Follow-up observations with the Keck I 10-meter telescope's Near Infrared Camera (NIRC) were conducted on 27 May 1999 and identified methane in 2MASS J1047+21's near-infrared spectrum, classifying it as a T-type brown dwarf.

Detection of radio emissions

In 2010, astronomers using the Arecibo Radio Telescope discovered bursts of low-frequency radio waves coming from 2MASS J1047+21. This radio emission comes from electrons spiraling around the magnetic field lines of the brown dwarf. Since the frequency of the radio emission is linked to the strength of the magnetic field, the team measured a magnetic field strength of 1.7 kG. The bursts were also found to drift in frequency, in a manner reminiscent of certain types of solar radio emission. The radio emissions, together with the detection of Hα, which is usually found in stellar chromospheres, shows that 2MASS J1047+21 is magnetically active.