Arman777 said:
I thought this problem is the first or recent founded contradiction with the CDM model.
You were wrong.
Serious problems with the CDM model were identified, overwhelming, and basically irrefutable at least as far back as six years ago. Consider an excerpt from
this September 2011 paper:
Evidence that Cold Dark Matter (LambdaCDM) and its proposed tailored cures do not work at small scales is staggering. . . .The most troubling signs of the failure of the CDM paradigm have to do with the tight coupling between baryonic matter and the dynamical signatures of DM in galaxies, e.g. the Tully-Fisher relation, the stellar disc-halo conspiracy, the maximaum disc phenomenon, the MOdified Newtonian Dynamics (MOND) phenomenon, the baryonic Tully-Fisher relation, the baryonic mass discrepancy-acceleration relation, the 1-parameter dimensionality of galaxies, and the presence of both a DM and a baryonic mean surface density. . . .
It should be recalled that the connection between small scale structure features and the mass of the DM particle follows mainly from the value of the free-streaming length lfs. Structures smaller than lfs are erased by free-streaming. . . . 100 GeV CDM particles produce an extremely small lfs ∼ 0.1 pc. While the keV . . . CDM lfs . . . produces the existence of too many small scale structures till distances of the size of the Oort’s cloud in the solar system. No structures of such type have ever been observed. Also, the name CDM precisely refers to simulations with heavy DM particles in the GeV scale. . . . The mass of the DM particle with the free-streaming length naturally enters in the initial power spectrum used in the N-body simulations and in the initial velocity.
Even in 2011, the evidence that there were serious problems with cold dark matter models had been accumulating for years. So, this is really nothing new.
You go on to state:
I know that there's some DM density profiles that can explain some structers but in general yes there's still a lots of gaps and these discoveries show us that there's also something wrong with CDM model.
As I note it has been clear that the CDM model was profoundly broken six years ago and subsequent efforts to cure it with more sophisticated simulations have not been successful. Instead, increased volumes of evidence have continued to provide more evidence that this is not the answer. The sub-type of CDM model that was once most popular, the supersymmetric WIMP, has been pretty definitively disproven.
So we have no explanation for DM again? Like we should re-consider most of things or still our CDM theories applied in general ? Like do we need some adjusments or a whole new theory about it? Isnt this make sense? I mean why should expect more denser DM around small galaxies ? Or Its just about the problem of models?
There is no currently outstanding dark matter model that is a good fit to the data. Some are better than others, but all of them have serious problems fitting the data.
"Warm dark matter" models (in which dark matter particles have masses on the order of a keV instead of "Cold dark matter" models on the order of 1-100 GeV, are a better fit to the data, and direct dark matter models have not ruled out weakly interacting warm dark matter (mostly because the current experiments are incapable of distinguishing dark matter from ordinary neutrinos at low masses), but high energy physics experiments like LEP, Tevatron and the LHC strongly disfavor weakly interacting dark matter particles with masses of less than 45 GeV. So, any warm dark matter particle would have to be "sterile". Unfortunately for warm dark matter, even sterile warm dark matter models still share some significant problems with cold dark matter models.
A host of other more complex dark matter models, such as self-interacting dark matter models, are also in trouble.
Dark matter models still do much better at matching reality than a universe with only ordinary matter and only general relativity. And, not every possible dark matter model in "theory-space" has been ruled out yet. But, the house of dark matter models is starting to look like a horror movie. There are dead theories everywhere, every time you turn around another one dies, and the astronomers whose observations are killing them are churning out new data limiting dark matter parameter space faster than a horror movie can grow a zombie swarm.
This isn't to say that the astronomers are only aiming their sights at dark matter models. The set of modified gravity theories was smaller than the set of dark matter theories in the first place, and several of them have also fallen prey to experimental falsification. For example, Verlinde's new "emergent gravity" theory was a case of infant mortality that was ruled out just months after it was proposed.
Of course, like the dead dark matter theories, the falsified modified gravity theories are still better fits to observation than ordinary matter and general relativity alone. Better yet, they provide better intuition about dark matter phenomena and have been more successful at predicting new dark matter phenomena than dark matter models. But, there are now at least as many, if not more, viable modified gravity theories as there are viable dark matter particle theories (although, in fairness, this is partially because less effort has been devoted to comparing modified gravity theories to the data).
