  The $X(3872)$, whose mass coincides with the $D^0\bar D^{*0}$ threshold, is
the most extended hadron object. Since its discovery in 2003, debates have
never stopped regarding its internal structure. We propose a new object, the
$X$ atom, which is the $D^\pm D^{*\mp}$ composite system with positive charge
parity and a mass of $(3879.89\pm0.07)$ MeV, formed mainly due to the Coulomb
force. We show that a null signal of the $X$ atom can be used to put a lower
limit on the binding energy of the $X(3872)$. From the current knowledge of the
$X(3872)$ properties, the production rate for the $X$ atom relative to the
$X(3872)$ in $B$ decays and at hadron colliders should be at least
$1\times10^{-3}$. New insights into the $X(3872)$ will be obtained through
studying the $X$ atom.
