Undergrad Mass distribution in a celestial system

[Ranku]

If two sets of objects, of similar size but different mass, were to be part of a rotating celestial system, how differently would they be distributed? Would the distribution of the lower-mass objects be more spread out, while the higher-mass objects would be concentrated toward the centre?

 

[Hornbein]

If two sets of objects, of similar size but different mass, were to be part of a rotating celestial system, how differently would they be distributed? Would the distribution of the lower-mass objects be more spread out, while the higher-mass objects would be concentrated toward the centre?

I'm no expert but I can say that our solar system does not follow this hypothesis. The four high mass planets are quite far out. The lower mass asteroids are most concentrated in the middle, between Mars and Jupiter.

Everything experiences the same acceleration due to gravity so I don't expect mass to have anything to do with distance from the center.

 

[Ibix]

I'd say there were too many variables in that to answer. If the bodies are more or less space-filling then I'd expect the denser ones to sink under their own self-gravity. But if the densities are wildly different you might end up with the dense bodies each surrounded by its own "atmosphere" of low density objects, but otherwise behaving more or less as if the low density ones didn't exist. And @Hornbein has a different reading.

I suspect that there are other interpretations possible. What sort of spacing, density ratio, average mass, average kinetic energy, etc did you have in mind, @Ranku?

 

[Ranku]

I suspect that there are other interpretations possible. What sort of spacing, density ratio, average mass, average kinetic energy, etc did you have in mind, @Ranku?

I had in mind a galaxy with matter and dark matter mix. I was wondering if the distribution of matter and dark matter, with much of matter concentrated toward the centre, and dark matter dispersed much further, could in some way be indicating that dark matter is lighter than matter.

 

[Ibix]

No. That kind of separation between heavy and light species can happen, but it requires the species to be able to collide so that they can exclude one another from "their" region. Dark matter does not collide, neither with itself nor with matter, because it does not interact electromagnetically. Thus it can't separate out like species in a fractionating column.

The dark matter halo arises because of that lack of collision. Dark matter doesn’t collide, so it doesn’t heat up and end up radiating away its kinetic energy. Thus it keeps flying around at higher speeds than normal matter, and doesn’t clump into planets and stars.

 

[snorkack]

No. That kind of separation between heavy and light species can happen, but it requires the species to be able to collide so that they can exclude one another from "their" region. Dark matter does not collide, neither with itself nor with matter, because it does not interact electromagnetically. Thus it can't separate out like species in a fractionating column.

But dark matter does interact gravitationally, including with matter. A hyperbolic flyby is an elastic collision.

 

[Ranku]

But dark matter does interact gravitationally, including with matter. A hyperbolic flyby is an elastic collision.

So if there is elastic collision, then can the process of separation of species between (heavier) matter and (lighter) dark matter in terms of their distribution occur after all, due to gravitational interaction - though the distribution would be somewhat different than what it would have been in collisional interaction.