The KBC void and Hubble tension contradict ΛCDM on a Gpc scale - Milgromian dynamics as a possible solution

The KBC void is a local underdensity with the observed relative density contrast delta equivalent to 1 - rho/rho(0) = 0.46 +/- 0.06 between 40 and 300 Mpc around the Local Group. If mass is conserved in the Universe, such a void could explain the 5.3 sigma Hubble tension. However, the MXXL simulation shows that the KBC void causes 6.04s tension with standard cosmology (Lambda CDM). Combined with the Hubble tension, Lambda CDM is ruled out at 7.09 sigma confidence. Consequently, the density and velocity distribution onGpc scales suggest a long-range modification to gravity. In this context, we consider a cosmologicalMONDmodel supplemented with 11 eV/c(2) sterile neutrinos. We explain why this.HDM model has a nearly standard expansion history, primordial abundances of light elements, and cosmic microwave background (CMB) anisotropies. InMOND, structure growth is self-regulated by external fields from surrounding structures. We constrain our model parameters with the KBC void density profile, the local Hubble and deceleration parameters derived jointly from supernovae at redshifts 0.023-0.15, time delays in strong lensing systems, and the Local Group velocity relative to the CMB. Our best-fitting model simultaneously explains these observables at the 1.14 per cent confidence level (2.53 sigma tension) if the void is embedded in a time-independent external field of 0.055 a(0). Thus, we show for the first time that the KBC void can naturally resolve the Hubble tension in Milgromian dynamics. Given the many successful a priori MOND predictions on galaxy scales that are difficult to reconcile with Lambda CDM, Milgromian dynamics supplemented by 11 eV/c(2) sterile neutrinos may provide a more holistic explanation for astronomical observations across all scales.