If the mid size (less than 4000 solar mass) black hole has a cross sectional area of the event horizon of 1000 square kilometers and is cutting though the solar wind particles at 1000 kilometers per second (relative to the solar wind particles) it's radiation signature will will be different if the relative speed (or observation angle?) is different. We need to look from outside Earth's magnetoshere (or make lots of accomodations) for near by black holes passing though our Oort cloud. Are we planning a probe that is looking for such anomolies in the solar wind particles? My guess is the gravity pertubations of the 4 old probes leaving our solar system, are more detectable than the radiation, unless the black hole accreats an Oort cloud object, bigger than a tenis ball or already has a more significant accreation disk. Did I just solve the mystery of why the Oort cloud probes are mysteriously accellerating? They are each approching a black hole? Not likely that there are 4 black holes producing the same acceleration of each probe. Perhaps each of the probes are accelerating differently? Perhaps the volume just outside the event horizon does not produce a significant impact signature with the very thin Oort cloud solar wind particles? Can we detect the impact signature of Venus and Neptune which have much larger cross sectional area, but possibly slower than the black holes passing though our Oort cloud, if any? Why are we talking about thousand solar mass black holes instead of 20 solar mass black holes which might be typical of a single black hole merger? Neil