Brown dwarfs and the minimum mass of stars

Stars form from large clouds of gas and dust that contract under their own gravity. The birth of a star occurred when a fusion reaction of hydrogen into helium has ignited in its core. The key variable that determines the formation of a star is mass. If the mass of the contracting cloud is below certain minimum value, instead of a star, a substelar object -- known as a brown dwarf -- will form. How much mass is required for a star to form? This article aims to answer this question by means of a simple heuristic argument. The found value is 0.016 solar masses, which is of the same order of magnitude as the accepted value 0.08 solar masses. This article may be useful as pedagogical material in an introductory undergraduate astronomy course.