{{Short description|Parameterization}} The '''singular isothermal sphere (SIS) profile''' is the simplest parameterization of the spatial distribution of matter in an astronomical system (e.g. galaxies, clusters of galaxies, etc.).<ref>{{cite arXiv |first=C. |last=Keeton |date=June 2002 |title=A Catalog of Mass Models for Gravitational Lensing |eprint=astro-ph/0102341v2 }}</ref>
==Density distribution== <math> \rho(r) = \frac{\sigma_{V}^{2}}{2\pi G r^{2}} </math>
where σ<sub>V</sub><sup>2</sup> is the velocity dispersion and G is the gravitational constant. The SIS profile is unphysical because of the singularity at zero radius and the fact that the total mass calculated by integrating the function out to infinite radius does not converge (i.e., is infinite). However, it is commonly utilized in the literature due to the simplicity of its form.
==See also== *Navarro-Frenk-White profile
==References== {{reflist}}
Category:Large-scale structure of the cosmos Category:Equations of astronomy