Speaker
Description
We report the first detection of brightness variability in an extremely metal-poor brown dwarf. These objects are ancient, very low-mass members of the Milky Way that formed when the Galaxy contained far fewer heavy elements than it does today. Using the 10.4-m Gran Telescopio Canarias, we found that the nearest known extreme T subdwarf, WISEA,J181006.1$-$101000.5, changes its $J$-band brightness by $1.14\pm0.26%$ every $73.7\pm1.5$ minutes. We interpret this periodic signal as the rotation of an uneven atmosphere into and out of view. The object completes a rotation about 8 times faster than Jupiter, similar to watching changing cloud patterns on a rapidly rotating Jupiter. An independent measurement of its projected rotational velocity, $v\sin i = 125^{+25}_{-23}\ {\rm km,s^{-1}}$, confirms that the object is an extremely fast rotator. Such rapid rotation may be a natural consequence of its old age and compact size: unlike stars, these ultracool objects have no efficient mechanism to slow their rotation over billions of years. This first detection opens a new window into the atmospheres and rotation of the oldest ultracool objects in the Galaxy.
