  We report the discovery of molecular gas streams orbiting around an invisible
massive object in the central region of our Galaxy, based on the
high-resolution molecular line observations with the Atacama Large
Millimeter/submillimeter Array (ALMA). The morphology and kinematics of these
streams can be reproduced well through two Keplerian orbits around a single
point mass of $(3.2 \pm 0.6)\times 10^4 \ M_\odot$. We also found ionized gas
toward the inner part of the orbiting gas, indicating dissociative shock and/or
photoionization. Our results provide new circumstantial evidences for a
wandering intermediate-mass black hole in the Galactic center, suggesting also
that high-velocity compact clouds can be probes of quiescent black holes abound
in our Galaxy.
