J1122+25 Could be the Fastest Spinning Brown Dwarf

As part of a search for flaring radio emissions from a sample of L and T brown dwarfs, Route & Wolszczan (2016) present the discovery of flares from a T6 brown dwarf identified as J1122+25. The flaring appears to be occurring with a stable recurrence period of 0.288 hours, or ~17 minutes. If this is indeed the rotation period of the brown dwarf, it is much shorter than the shortest rotation periods inferred from observations of photometric variability of brown dwarfs at optical/near-infrared wavelengths - 1.41 hours for the T6.5 brown dwarf J2228-43 and 1.55 hours for the T7 brown dwarf J0050-33.

Nevertheless, more work is still required to confirm if the flaring period of J1122+25 is really an indication of its rotation period. If J1122+25 is indeed rotating once every ~17 minutes, then its rotation velocity is likely to be much greater than 100 km/s. A Jupiter-sized brown dwarf with less than 80 times the mass of Jupiter can have a rotation period as short as ~20 minutes. In the case of J1122+25, its short rotation period of only ~17 minutes means that it has to be less than ~90 percent the size of Jupiter for it not to break apart.

Reference:
Route & Wolszczan (2016), "Radio Flaring from the T6 Dwarf WISEPC J112254.73+255021.5 with A Possible Ultra-short Periodicity", arXiv:1604.04543 [astro-ph.SR]