His goal was to use HST's sharp vision to image the galaxies which, according to current theories, should act as hosts for the quasars insofar as they would provide fuel for the presumed supermassive black hole at the heart of the quasar.
Host galaxies are hard to see because of the glare from the quasar itself.
In Bahcall's sample of 14, several host galaxies were found, but for 8 quasars no hosts were found.