# Jeans Length/Cloud Collapse

1. Feb 25, 2013

### AbsoluteZer0

Hello,

As I understand, the following formula describes the Jeans length.

$\lambda_j = \sqrt\frac{15k_BT}{4\pi G \mu P}$

Where $\mu$ is the mass per particle.

Forgive me if this question may come across as relatively stupid, I imagine that each of the particles within the cloud should have different masses. Is $\mu$ an average of the masses?

2. Feb 26, 2013

### SHISHKABOB

Yeah it is, but since most gas is generally ~75% H and ~25% He or something close to that, it's easy to figure out the average mass per particle.

3. Feb 26, 2013

### Chronos

It's one of those n-body things where you must approximate to get a numerical solution.