Magnetospheric processes seen in gas giants such as aurorae and circularly polarized cyclotron maser radio emission have been detected from some brown dwarfs. However, previous radio observations targeted known brown dwarfs discovered via their infrared emission. Here we report the discovery of BDR J1750+3809, a circularly polarized radio source detected around 144 MHz with the Low-Frequency Array (LOFAR) telescope. Follow-up near-infrared photometry and spectroscopy show that BDR J1750+3809 is a cold methane dwarf of spectral type T6.51 at a distance of . The quasi-quiescent radio spectral luminosity of BDR J1750+3809 is ≈5נ10¹⁵ erg s⁻¹ Hz⁻¹, which is over two orders of magnitude larger than that of the known population of comparable spectral type. This could be due to a preferential geometric alignment or an electrodynamic interaction with a close companion. In addition, as the emission is expected to occur close to the electron gyrofrequency, the magnetic field strength at the emitter site in BDR J1750+3809 is B≳25 G, which is comparable to planetary-scale magnetic fields. Our discovery suggests that low-frequency radio surveys can be employed to discover substellar objects that are too cold to be detected in infrared surveys.

气体巨星（如极光和圆极化回旋加速器maser无线电发射）中所见的磁层过程已从一些褐矮星中检测到。但是，先前的无线电观测以通过红外发射发现的已知褐矮星为目标。在这里，我们报告发现了BDR J1750 + 3809，它是用低频阵列（LOFAR）望远镜在144 MHz附近检测到的圆极化无线电源。后续的近红外光度法和光谱学表明，BDR J1750 + 3809是光谱类型为T6.51的冷甲烷矮星，距离为。BDR J1750 + 3809的准静态无线电频谱亮度为≈5נ10 ¹⁵ erg s ^-1 Hz ^-1比已知光谱类型的已知种群大两个数量级。这可能是由于优先的几何排列或与紧密伴侣的电动相互作用。另外，作为发射预期出现接近电子回转频率，在BDR J1750 + 3809发射站点的磁场强度是乙≳25G，这与行星尺度磁场。我们的发现表明，可以使用低频无线电勘测来发现太冷而无法在红外勘测中检测到的亚星体。