The VLA radio telescope in New Mexico listened to the sky for two sessions of 96 minutes each and caught short radio bursts from the object 2M2228—a brown dwarf. This cosmic body is heavier than a planet but lighter than a star: thermonuclear reactions never ignite in its core, so it simply cools over time. The flares arrived with intervals of 47 minutes during the first session and 58 minutes during the second.
The signal turned out to be strongly polarized — the radio waves oscillated predominantly in one direction, as if they had passed through a grid. Such behavior is typical of radiation from electrons spiraling around magnetic field lines. From the strength of the flares, astronomers estimated the dwarf's magnetic field: it is no weaker than 1.4 kilogauss — hundreds of times stronger than Earth's magnetic field. The researchers suspect this is the same mechanism that produces auroras on Jupiter, but much more powerful.
The observations are still short, and the flare periods may be refined. But it is already clear that 2M2228 is a convenient target for future coordinated observations with radio telescopes and the James Webb Space Telescope. This could test whether the radio flares are linked to weather in the brown dwarf's atmosphere and how its magnetic field drives the auroras.
as written by the authors arXiv:2601.04158
We present the detection of 2MASS J22282889-4310262 (2M2228), a T6/T6.5 brown dwarf, using the Karl G. Jansky Very Large Array (VLA) archival data observed at C band (4-8 GHz) over two observing epochs ($$2\times96$$ minutes). 2M2228 is detected at time and frequency averaged Stokes I and V peak flux densities of $$67.3\pm4.9\ \mu\ \rm{Jy beam}^{-1}$$ and $$14.4\pm3.0\ \mu\text{Jy beam}^{-1}$$ in the first epoch and $$107.2\pm5.2\ \mu\rm{Jy\ beam}^{-1}$$ and $$-20.7\pm1.2\ \mu\text{Jy beam}^{-1}$$ in the second epoch. This discovery constitutes the eighth and, notably, the most rapidly rotating T dwarf detected to date at radio wavelengths. Our observations reveal highly polarised bursts at fractional polarisation ratios $$f_\text{c}>50$$%. Using Stokes I light curves, we measure occurrence intervals of $$\sim47$$ and $$\sim58$$ minutes in the two observing epochs respectively with the first burst aligning within a half period timescale of the the previously measured mid infrared photometric period of $$85.8\pm0.32$$ minutes. We attribute the emission to the electron cyclotron maser emission (ECME) and constrain the magnetic field strength to $$B\gtrsim1.4$$ kG. We emphasise that the periods inferred are provisional considering the short observing durations. The combination of previously demonstrated atmospheric stability and newly detected radio emission in 2M2228 makes it a promising laboratory for testing magnetospheric currents-driven auroral models and for guiding future coordinated James Webb Space Telescope (JWST) and radio observations to probe the link between auroral activity and atmospheric dynamics in T-type brown dwarfs.
Brown dwarfs are sometimes called "failed stars": they form like stars but lack the mass to ignite hydrogen fusion.