Quantity  Expression 

Length (R)  
Mass (M) 
Nbody units are a completely selfcontained system of units used for Nbody simulations of self gravitating systems in astrophysics. In this system, the base physical units are chosen so that the total mass, M, the gravitational constant, G, and the virial radius, R, are normalised. The underlying assumption is that the system of N objects (stars) satisfies the virial theorem. The consequence of standard Nbody units is that the velocity dispersion of the system is and that the dynamical crossing time scales as . The first mention of standard Nbody units was by Michel Hénon (1971).^{[1]} They were taken up by Haldan Cohn (1979)^{[2]} and later widely advertised and generalized by Douglas Heggie and Robert Mathieu (1986).^{[3]}

