Alternative to dark matter (not MOND)

[Jacques]

Hi all

I just had a thought that might explain the rotation curve of galaxies. It maybe wrong, I don't know but here it is:

The stars at the edge of spiral galaxies are going to fast to be kept in orbit only by the gravity of the visible matter. The main explaination is that there exist some unseen matter who was called dark matter.

My thought was: At these distances from the center of the galaxies the gravitationnal acceleration is very very small, so we don't need a big "force" to keep the stars on track around the center. Intergalactic space is almost empty of matter. Almost, a few atom per cubic meter or kilometer I don't remember, but it is not empty. And I think that these few atom are very energetic. Is it possible that this "intergalactic gas" exert a sufficient pression on galaxies to keep them from flying apart ?

I don't know the data and how this "pression" can be calculated, but I think someone may have figured it out...

Thanks

[timo]

The good-old pV=NkT with p being the pressure, V being a sample volume, N the number of particles in this sample volume, k the Boltzman-constant and T the temperature should work well here. You get T from your assumed energy-distribution of the particles. Do a few sample-calculations to see if you can get any relevant pressures with such a low density at all. Then, you'll have to qualitatively explain why the pressure distribution in the universe is such that pressure of your small particles is bigger outside the galaxies.