  Bound states of double-heavy tetraquarks are studied in a constituent quark
model. Two bound states are found for isospin and spin-parity I(J^P ) = 0(1^+)
in the bb\bar{u}\bar{d} channel. One is deeply bound and compact made of
colored diquarks, while the other is shallow and extended as a BB^* molecule.
The former agrees well with lattice QCD results. A systematic decrease in the
binding energy is seen by replacing one of the heavy quarks to a lighter one.
Altogether we find ten bound states. It is shown for the first time that
hadrons with totally different natures emerge from a single Hamiltonian.
