Hypothetical objects with masses exceeding 60 solar masses, the mass of the largest known ordinary stars (1 solar mass equals 4.4 × 10³⁰ lbm or 2 × 10³⁰ kg). The term is most often used in connection with objects larger than 10⁴ solar masses that might be the energy source in quasars and active galaxies. These objects not only are hypothetical but probably do not exist. However, their nonexistence is one of the major assumptions that makes the case for giant black holes, rather than supermassive stars, being the central engines of quasars. The description of supermassive stars presented here is based entirely on theoretical calculations.