the black ball, in the region of the manipūra-chakra, which coincides with the solar plexus. (The alchemical parallel to this is the ‘black sun.’) This means that the dark principle, or shadow, has been integrated and is now felt as a kind of centre in the body.
Jung explicitly equates the solar plexus with the manipura-chakra and interprets its activation as the somatic integration of the shadow, linking it to the alchemical ‘black sun.’
, Alchemical Studies, 1967thesis