Why is there no DM halo around the solar system?

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Discussion Overview

The discussion centers on the question of why there appears to be no dark matter (DM) halo surrounding the solar system. Participants explore theoretical explanations, mathematical considerations, and the implications of dark matter's properties in relation to baryonic matter.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that a central mass like the Sun would attract dark matter, leading to a spherically symmetric accumulation, similar to what is observed in galaxies.
  • Others argue that the density of dark matter in the vicinity of the solar system is so low that its gravitational effects are negligible compared to the mass of the Sun.
  • One participant calculates the amount of dark matter within the solar system's volume and compares it to the mass of the Sun, concluding that the dark matter's influence is minimal.
  • Another participant proposes that the calculations of dark matter density fail to account for the gravitational attraction of baryonic matter, suggesting that dark matter should concentrate more than current estimates indicate.
  • Some participants emphasize that dark matter does not interact like baryonic matter, lacking non-gravitational interactions that would allow it to clump together effectively.
  • There is a discussion about the time scales of contraction for dark matter halos around galaxies versus the solar system, with differing views on whether this affects detectability.
  • One participant presents an analogy comparing galaxies to bubbles and dark matter to water, suggesting a different perspective on their interaction.
  • Several participants acknowledge errors in calculations or assumptions, indicating ongoing refinement of their arguments.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the presence and behavior of dark matter around the solar system, with no consensus reached on the reasons for the apparent absence of a detectable halo.

Contextual Notes

Limitations include assumptions about dark matter's behavior, the dependence on gravitational interactions, and the complexity of calculating density and mass effects over time.

  • #61
Jonathan Scott said:
It's not true that DM doesn't interact at all; it's that it only interacts gravitationally.

It seems at least theoretically possible that if some effect causes it to focus into a narrower stream, then the self-gravitational attraction of that stream would refocus it weakly again later

I'm googling "DM density"...

http://arxiv.org/abs/1205.4033

"we find that the data imply a local dark-matter density of 0.008 +/- 0.003 Msun/pc^3 = 0.3 +/- 0.1 GeV/cm3"

This is way, way too low for gravitational self-interaction.
 
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  • #62
Jonathan Scott said:
I suspect that you'd require very special (physically implausible) conditions to focus the flow sufficiently accurately for the self-gravity to have enough effect to be noticeable.
Hi Jonathan:

I am not sure I understand the implications of self-gravity here. Are you saying that if a hair structure were to form (as apparently predicted by the Prezeau paper nikkkom cited in post #47) with the DM moving out of the space occupied by the hair as new DM moved into this space, that the DM in the hair would gravitationally influence the later DM being focused towards the hair in such a way that the hair structure would cease to exist?

Regards,
Buzz
 
  • #63
nikkkom said:
I'm googling "DM density"...

http://arxiv.org/abs/1205.4033

"we find that the data imply a local dark-matter density of 0.008 +/- 0.003 Msun/pc^3 = 0.3 +/- 0.1 GeV/cm3"

This is way, way too low for gravitational self-interaction.

But if you assume an unrealistically ideal uniform flow being focused in an unrealistically ideal mathematical way, you can achieve far higher densities. I'm not saying that's realistic physics, but it might account for the temporary "hair" formation in this simulation. However, I wouldn't expect it to be stable even in theory, so the flow would disperse more randomly afterwards.
 

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