The energy density of these systems is calculated by evaluating a non-elementary integral as the gamma function of 3 times Apéry's (“ah-pay-REEZ”) constant. These systems can be modeled as a cavity containing (10[1])a photon gas in equilibrium with a small (10[1])hole. Integrating (10[1])Lambert’s cosine law over frequency and solid angle gives a formula for the power per area of these systems. The dependence of these systems’ radiance on frequency is given by a cubic term over an exponential term minus 1. The power radiated by these systems is proportional to the fourth power (10[1])of temperature. (10[1])Planck’s (10[3]-5[1])(“plahnk’s”) law corrects these systems’ low-frequency approximation of the Rayleigh–Jeans law that predicts the “ultraviolet catastrophe.” For 10 points, name these objects that absorb all incoming radiation. ■END■ (0[1])