Most of Emden's work related to thermodynamics applied to natural phenomena, while his published papers focused on geophysics and astrophysics. Emden's book Gaskugeln: Anwendungen der mechanischen Wärmetheorie auf kosmologische und meteorologische probleme presented a mathematical model to explain the expansion and compression of gas spheres. The book also includes a short section on Karl Schwarzschild 's theory of convective equilibrium. Emden's work, in conjunction with Subrahmanyan Chandrasekhar, was named the Emden–Chandrasekhar equation. In a major advance over previous work, by introducing polytropic solutions, modelling of a much broader range of stellar objects was possible.