Undergrad Cuspy Halo Problem: Questions & Answers

[Arman777]

I have couple questions related to the Cuspy halo problem. First I want to start by telling what I understand from the problem.

Simulations shows that in the core of the low-mass galaxies dark matter density should increase sharply, however in real life the DM density increases linearly with respect to the radius. Is this true ?

Is this problem solved ?

Is this problem appears only on the low-mass galaxies or in all galaxies ?

How can we detect that these galaxies have low DM density in their cores ?

 

[George Jones]

Is this problem solved ?

See

https://www.physicsforums.com/threads/how-certain-is-dark-matter.952790/page-4#post-6045864
I don't know how accepted this work is, or how it goes in solving the problem. For a nice explanation, see, in particular, the tweets to which I linked.

 

[Arman777]

Thanks for the info. It seems a nice theory. Is someone knows why this happens only on the dwarf galaxies ? Or Is this theory accepted ?

 

[ohwilleke]

Simulations shows that in the core of the low-mass galaxies dark matter density should increase sharply, however in real life the DM density increases linearly with respect to the radius. Is this true ?

The cuspy halo problem has been explored most heavily in ordinary sized spiral galaxies, it is not primarily a low-mass galaxy issue.

Is this problem solved?

Multiple solutions have been proposed, none has won widespread acceptance. Warm dark matter particles, self-interacting dark matter particles and modified gravity theories have all been motivated in significant part, by a desire to address this problem.

Some theorists stick stubbornly to pure cold dark matter hypotheses and deny that halos differ from the NFW distribution theoretically predicted for cold dark matter, notwithstanding the evidence to the contrary. But, they are wrong.

Is this problem appears only on the low-mass galaxies or in all galaxies?

This isn't primarily a low-mass galaxy issue. Very large elliptical galaxies have little apparently dark matter relative to the luminosity by comparison to spiral galaxies and dwarf galaxies, so the issue is less intense in those cases.

How can we detect that these galaxies have low DM density in their cores ?

We detect DM density in the core of medium sized mostly spiral galaxies where this is observed mostly by inferring the shape of the halo from the dynamics of the stars in the galaxy and to a lesser extent with lensing measurements.

 

[ohwilleke]

See

https://www.physicsforums.com/threads/how-certain-is-dark-matter.952790/page-4#post-6045864
I don't know how accepted this work is, or how it goes in solving the problem. For a nice explanation, see, in particular, the tweets to which I linked.

Deur's work is unfortunately not widely accepted although there have been a number of peer reviewed articles by the author. http://dispatchesfromturtleisland.blogspot.com/p/deurs-work-on-gravity-and-related.html

But, I don't think that this is the quote that you intended to put in your post. I think you intended instead to quote the post immediately after the one that your quoted with the twitterverse link.

 

[Arman777]

The cuspy halo problem has been explored most heavily in ordinary sized spiral galaxies, it is not primarily a low-mass galaxy issue.
Multiple solutions have been proposed, none has won widespread acceptance. Warm dark matter particles, self-interacting dark matter particles and modified gravity theories have all been motivated in significant part, by a desire to address this problem.

Some theorists stick stubbornly to pure cold dark matter hypotheses and deny that halos differ from the NFW distribution theoretically predicted for cold dark matter, notwithstanding the evidence to the contrary. But, they are wrong.
This isn't primarily a low-mass galaxy issue. Very large elliptical galaxies have little apparently dark matter relative to the luminosity by comparison to spiral galaxies and dwarf galaxies, so the issue is less intense in those cases.
We detect DM density in the core of medium sized mostly spiral galaxies where this is observed mostly by inferring the shape of the halo from the dynamics of the stars in the galaxy and to a lesser extent with lensing measurements.

Sorry for my late reply, but I want to ask more about it .. So In normal case I expect that there should me more dark matter wrt to the outer layers of the galaxies. I mean density at the galatic center shoul be higher or similar to the outer layers of the galaxy.

I am kind of puzzled why we observe the exact opposite (DM density increases as R from the galatic center) ?

Is this part of a cusp/core problem ? I mean it seems that N body simulations should give the correct answer.
Dark matter at the galactic center should be higher. Why at the near center baryonic mass density is larger than the DM density ? Is this always the case ?