Black hole shadows can't distinguish dark matter profiles in galactic centers

Using the Newman-Janis algorithm, the authors construct rotating black hole solutions embedded in King, Hernquist, and Moore dark matter halo profiles and compute their shadows. While dark matter slightly enlarges the shadow compared to a pure Kerr black hole, the effect is negligibly small across all three profiles regardless of whether the halo is cuspy or cored. The spin parameter, characteristic density, and halo radius all leave similarly faint imprints. The upshot: shadow observations — even high-precision ones — are unlikely to discriminate between competing dark matter distributions near galactic centers.