Despite the presence of the Milky Way, several active galaxies are visible in Serpens Cauda as well, such as PDS 456, found near Xi Serpentis. The most intrinsically luminous nearby active galaxy,[149] this AGN has been found to be extremely variable in the X-ray spectrum. This has allowed light to be shed on the nature of the supermassive black hole at the center, likely a Kerr black hole.[150] It is possible that the quasar is undergoing a transition from an ultraluminous infrared galaxy to a classical radio-quiet quasar, but there are problems with this theory, and the object appears to be an exceptional object that does not completely lie within current classification systems.[149] Nearby is NRAO 530, a blazar that has been known to flare in the X-rays occasionally.