  Bose-Einstein condensates (BECs) confined on shell-shaped surfaces have been
proposed as a platform for exploring many nontrivial quantum phenomena on
curved spaces. However, as the shell-shaped trapping potential generated with
the conventional radio frequency dressing method is very sensitive to gravity,
so far experimental studies of shell BECs can only be performed in
micro-gravity environments. Here, we overcome this difficulty and create a
shell BEC in the presence of Earth's gravity with immiscible dual-species BECs
of sodium and rubidium atoms. After minimizing the displacement between the
centers of mass of the two BECs with a magic-wavelength optical dipole trap,
the interspecies repulsive interaction ensures the formation of a closed shell
of sodium atoms with its center filled by rubidium atoms. Releasing the double
BEC together from the trap, we observe explosion of the filled shell
accompanied by energy transfer from the inner BEC to the shell BEC. With the
inner BEC removed, we obtain a hollow shell BEC which shows self-interference
as a manifestation of implosion. Our results pave an alternative way for
investigating many of the intriguing physics offered by shell BECs.
