# Interstellar Medium

1. May 23, 2007

### popffabrik1

Hey, can anybody tell me what the estimate is on the mean mass of a particle in the interstellar medium? I would guess around 1-10 proton masses?

2. May 23, 2007

### marcus

Just for fun, I will guess too.
I think you probably mean the ISM in the plane of our galaxy

I think you mean to average on a MASS basis.

So if most of the mass is in the form of neutral gas, then for a first approximation of the average, I can neglect dust and ionized stuff.

Eventually someone who has a definite figure will reply. I would guess the average atomic weight is 2.
(because I think the ISM is dominated by molecular hydrogen.
there would also be some neutral atomic hydrogen with weight 1 but that would tend to be balanced out by the heavier molecular species and the dust)

BTW welcome to physicsforums, Mr. Popffabrik.
I like the name, it seems it could be a nickname for the LHC collider. "bang factory"

Last edited: May 23, 2007