Spatial Pattern Formation of an Interstellar Medium

The population dynamics of a multi-phased interstellar medium (ISM) was investigated using a lattice model in the position-fixed reaction limit, which was originally developed for use regarding ecosystems. We assumed three components of the medium in interstellar space: cold clouds, warm gas, and hot gas. Interactions between distinct phases of gas give rise to cyclic phase changes in ISM. Such local phase changes are propagated in space, and a stochastic stationary pattern is finally self-organized. We obtained the following two characteristic patterns: (1) When the sweeping rate of a warm gas into a cold component is relatively high, cold clouds associated with the warm gas form small-scale clumps and are dispersively distributed all over space, whereas a large fraction of the region is covered by hot gas. (2) When the sweeping rate is relatively low, in contrast, the hot-gas component is relatively localized, while cold clouds prevail throughout the region.