  In this letter, the exact accelerating string solution of a heavy
quark-antiquark pair is found in $AdS_5$ space. On the accelerating string,
there is a particular scale which separates the radiation and the heavy quark.
This scale is explicitly shown to be an event horizon in the proper frame of
the heavy quark. Furthermore, we find a new correspondence, which relates the
horizon in $AdS_5$ space on the gravity theory side to the Unruh temperature in
Minkowski space on the field theory side of the AdS/CFT correspondence.
$p_{\perp}$-broadening and $p_{L}$-broadening of the heavy quark due to
radiation are computed using the AdS/CFT correspondence.
