---
id: physics-collapse
title: Collapse Models
---

# Collapse Models

**Main Contributors**: Felix Priestley

The freefall collapse function used to control the density in most UCLCHEM models is fairly simplistic. [Priestley et al. 2018](https://dx.doi.org/10.3847/1538-3881/aac957) created the collapse model which parameterizes the density profile of a collapsing core as a function of time and radius. The following collapse modes are possible:

-   "BE1.1": Bonnor-Ebert sphere, overdensity factor 1.1 (Aikawa+2005)
-   "BE4": Bonnor-Ebert sphere, overdensity factor 4 (Aikawa+2005)
-   "filament": magnetised filament, initially unstable to collapse (Nakamura+1995)
-   "ambipolar": magnetised cloud, initially stable, collapse due to ambipolar diffusion (Fiedler+1993)