... Hubble Heritage Project . ... Science Projects . ... This study (analogous to luminosity-function determinations for galaxies) sets the resolution demand for the UV telescope by asking to study the sphere of influence of the central objects in AGNs. Four milliarcsecond angular resolution meets this need, for the largest black holes, anywhere in the Universe. The study demands full aperture, not interferometry, because of the large number of objects that need to be measured. ...