Even considering baryon effects, cold dark matter models don't match astronomy observations at the scale of galaxies.
In cosmological N-body simulations, the baryon effects on the cold dark matter (CDM) halos can be used to solve the small scale problems in ΛCDM cosmology, such as cusp-core problem and missing satellites problem. It turns out that the resultant total density profiles (baryons plus CDM), for halos with mass ranges from dwarf galaxies to galaxy clusters, can match the observations of the rotation curves better than NFW profile. In our previous work, however, we found that such density profiles fail to match the most recent strong gravitational lensing observations.
In this paper, we do the converse: we fit the most recent strong lensing observations with the predicted lensing probabilities based on the so-called (α,β,γ) double power-law profile, and use the best-fit parameters (α=3.04,β=1.39,γ=1.88) to calculate the rotation curves. We find that, at outer parts for a typical galaxy, the rotation curve calculated with our fitted density profile is much lower than observations and those based on simulations, including the NFW profile. This again verifies and strengthen the conclusions in our previous works: in ΛCDM paradigm, it is difficult to reconcile the contradictions between the observations for rotation curves and strong gravitational lensing.
Lin Wang, Da-Ming Chen, Ran Li "The total density profile of DM halos fitted from strong lensing" (July 31, 2017).
As the body text explains:
It is now well established that, whatever the manners the baryon effects are included in the collisionless CDM N-body cosmological simulations, if the resultant density pro- files can match the observations of rotation curves, they cannot simultaneously predict the observations of strong gravitational lensing (under- or over-predict). And for the case of typical galaxies, the reverse is also true, namely, the SIS profile preferred by strong lensing cannot be supported by the observations of rotation curves near the centers of galaxies.
The cold dark matter paradigm has been dead for a while, and each new paper seems to further refute it. This paper comes close on the heels of findings that (1) sterile particle dark matter models, in general, are inconsistent with observation, (2) baryon effects cannot save CDM models when tested using a methodology different than the one in this new paper, and (3) the collision velocities seen in the Bullet Cluster are inconsistent with particle dark matter models. Of course, direct dark matter detection experiments looking for WIMPs continue to come up empty.
In addition to all of these problems generally applicable to Cold Dark Matter, MACHO candidates have also been directly ruled out for much of their parameter space.
In addition to all of these problems generally applicable to Cold Dark Matter, MACHO candidates have also been directly ruled out for much of their parameter space.
Self-interacting dark matter (SIDM) models are likewise very hard to fit to the observational evidence. As a recent paper sums up the situation for SIDM models: "these constraints rule out the entire parameter space where the self-scattering cross section can be relevant for astrophysical systems." Axion-like Fuzzy Dark Matter models are likewise in trouble.
Warm dark matter models aren't quite as deeply in trouble but they have a very narrow remaining parameter space (also here) and share problems common to sterile particle dark matter models and particle dark matter models generally.
Another limitation on fermion particle dark matter parameter space derives from the impact that dark matter particles with certain parameters would have on the temperature of neutron stars, although at least once precise neutron star temperature measurement is necessary before this can be converted into a viable means of dark matter detection.
Modified gravity theories have to be taken seriously at this point primarily because the particle dark matter alternatives are pretty much ruled out by observational evidence. At least some of these modified gravity theories, however, can fit the data in a wide array of circumstances where particle dark matter theories cannot.
Modified gravity theories have to be taken seriously at this point primarily because the particle dark matter alternatives are pretty much ruled out by observational evidence. At least some of these modified gravity theories, however, can fit the data in a wide array of circumstances where particle dark matter theories cannot.
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