Given

     Quasar luminosity        L  =  4 x 10^(38) Joule/sec

     Black hole mass          M  =  1 x 10^6 solar masses  =  2 x 10^(36) kg


   How many kg of matter per second must we drop into the black hole
   for the conversion of GPE into KE to match the quasar's luminosity?



       We know that for a black hole of 1 million solar masses, 
       a single kg of matter dropped from a great distance will generate

              drop 1 kg   -->     4.5 x 10^(16)  Joules 


       So in order to generate the luminosity of the quasar, we need
       to drop every second


                                      4 x 10^(38) Joule/sec
                rate of mass       ---------------------------
                                      4.5 x 10^(16) Joule/kg


                                =     9 x 10^(21) kg/sec



        This is very roughly 1/1000 the mass of the Earth.