Inferred Dark Matter Cores Are Indifferent To Baryonic Physics

Lots of dark matter models of galaxies rely on baryonic feedback (i.e. influence from ordinary matter) to account for its dark matter halo distributions. But a new paper states that the inferred core of a dark matter distribution over many galaxies is indifferent to the distribution of baryonic matter, which undermines this approach.

We present the first dark matter density profile derived directly from James Webb Space Telescope JADES Data Release~3 NIRSpec observations of N=587 galaxies spanning the cosmic noon epoch 1.5 ≤ z ≤ 3.5. From each NIRSpec G235M/G395M spectrum we extract the Hα emission-line velocity dispersion σha, stack galaxies in four redshift bins of Δz=0.5, and reconstruct representative group rotation curves within the General Theory of Relativity. Fitting the four-parameter modified exponential model and deriving the exact GTR energy density, we reduce the profile to a compact [2/3] Padé approximant with all coefficients determined in closed form from JWST observations. The profile is cusp-free, fully analytic, and redshift-dependent. Energy conditions, causality, and orbital stability are all satisfied. Most strikingly, the central density ρ(0) varies by less than 15% across z=1.5--3.5 despite a 35% decline in the asymptotic rotation velocity, revealing a universal dark matter core saturation density at cosmic noon decoupled from baryonic evolution.

Aritra Sanyal, Farook Rahaman "The New Dark Matter Density Profile from JWST JADES Galaxies" arXiv:2609.14071 (September 12, 2026).

Another paper also looks at inferred dark matter halo distributions, and, yet again (confirming perhaps dozens, if not hundreds, of previous papers), the distributions are not a good fit to the theoretically mandated NFW distribution for collisionless dark matter which is widely used by astrophysicists nonetheless.

We fit the circular velocity data, derived from weak lensing observations of isolated galaxies selected from the KiDS survey in four baryonic mass bins, using three different dark matter profiles. These include NFW, Burkert, and pseudo-isothermal profile. We find that the NFW and Burkert profiles cannot adequately fit the circular velocity data for all the four baryonic mass bins, whereas only the pseudo-isothermal profile can fit the data for all the four bins.

Sri Devaki Meduri, Shantanu Desai, "A comprehensive assessment of weak-lensing inferred circular velocity profiles of isolated galaxies" arXiv:2609.14085 (September 12, 2026).

See also, again undermining the baryonic feedback solution to the core-cusp problem of cold dark matter particle theories, this paper:

Baryonic feedback in hydrodynamical simulations is typically invoked to alleviate the core--cusp problem in dwarf galaxies. Yet baryonic processes also induce adiabatic contraction of dark matter, producing overly steep density profiles and excessively high dark matter fractions in the inner regions of massive galaxies. The dark matter distribution of galaxies across a wide stellar-mass range is therefore a critical test for such simulations, but a comprehensive benchmark has remained absent. 

Here, we consistently measure the dark matter distribution from galaxy centres out to radii of 20--50 kpc for 136 nearby galaxies that together span the local mass--size relation over the stellar mass interval 10^9 -10^11.5 M⊙. We identify central regions with lower dark matter densities relative to ΛCDM simulation expectations---whose extent grows from about 10 kpc to >50 kpc as stellar mass increases from 10^10M⊙ to 10^11.5M⊙. Although their physical origin remains unclear, these low--dark matter regions are clearly indicated by the data. Our results provide an important observational benchmark for future hydrodynamical simulations that explore alternative dark matter models and feedback processes.

Yu Lei, et al., "Lower central dark matter densities in nearby galaxies than predicted by simulations" arXiv:2609.16740 (September 15, 2026) (Accepted in principle by Nature Astronomy).