  The tunneling of composite systems, where breakup may occur during the
barrier penetration process is considered in connection with the fusion of
halo-like radioactive, neutron- and proton-rich nuclei on heavy targets. The
large amount of recent and new data clearly indicates that breakup hinders the
fusion at near and below the Coulomb barrier energies. However, clear evidence
for the halo enhancements, seems to over ride the breakup hindrance at lower
energies, owing, to a large extent, to the extended matter density
distribution. In particular we report here that at sub-barrier energies the
fusion cross section of the Borromean two-neutron halo nucleus $^{6}$He with
the actinide nucleus $^{238}$U is significantly enhanced compared to the fusion
of a no-halo $^{6}$He. This conclusion differs from that of the original work,
where it was claimed that no such enhancement ensues. This sub-barrier fusion
enhancement was also observed in the $^{6}$He + $^{209}$% Bi system. The role
of the corresponding easily excitable low lying dipole pygmy resonance in these
systems is therefore significant. The consequence of this overall enhanced
fusion of halo nuclei at sub-barrier energies, on stellar evolution and
nucleosynthesis is evident.
