The document discusses accretion processes around compact objects like black holes. It notes that up to 50% of stars exist in binary systems, meaning there may be millions of binary systems containing a black hole. As material spirals inward due to friction, energy is released and the spectrum and luminosity of the outgoing radiation depends on the accretion rate. At subcritical rates, the disk luminosity is around 1034-1036 erg/sec and the maximum temperature reaches 3x105-106 K in the inner disk. The frequency dependence of radiation intensity can be approximated as ν-1/3. Theories of disk accretion at subcritical regimes are discussed, assuming Newtonian mechanics and taking the inner disk boundary to be 3 gravitational