  By the AdS/CFT correspondence, the expectation value of certain local
operators in the CFT is given by the asymptotic value of supergravity fields.
We show that these local expectation values contain a remarkable amount of
information about small sources deep inside AdS_p x S^q. In particular, they
contain essentially all the multipole moments. More importantly, one can use
them to determine the size of a spherical source. This is not a small effect:
The size appears in an exponentially large contribution to the expectation
values. This provides an easy way for the CFT to distinguish stars from black
holes with the same mass, or to distinguish different "giant graviton"
configurations.
