Q:  A typical white dwarf is the size of the Earth (R = 6370 km)
             and has a temperature of T = 10,000 K.
             Assume that it emits like a blackbody
             (and recall that sigma = 5.67 x 10^(-8)  W/m^2 K^4)

      What is the luminosity of such a star?

      How does it compare to the luminosity of the Sun (L = 3.8 x 10^26 W)?


         Using the blackbody formula,

   
              L  =  (4 pi R^2) * (sigma * T^4)  


                 =  2.89 x 10^(23)  J/s


      Compared to the Sun,


              L(wd)          2.89 x 10^(23) J/s
            ---------  =   ----------------------------  =  0.00076
             L(Sun)          3.8  x 10^(26) J/s