In modelling galaxy structure formation, neither Cold Dark Matter (CDM) nor canonical Modified Newtonian Dynamics (MOND) (Milgrom [1]) can easily accommodate the recently discovered appearance of massive galaxies at early times [2]. We propose a new single-metric universe which fits within MOND in that there is no new matter in the stress-momentum tensor. In this the constant phenomenological acceleration scale a0 of the canonical MOND, below which Newtonian gravity is modified [1], now depends on the background matter density, effectively as a0 ~ H^2r, where r is the relevant distance scale. As a result, there are additional strong MOND-like forces at high redshifts sufficient, we believe, to trigger galaxy formation at early times. Our model looks old-fashioned in that it superficially resembles a vacuole model wtih all the artificialities that this implies. It differs in that it interpolates smoothly between the Schwarzschild metric at small scales and the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric at large scales without discrete boundaries. Within the framework of interpolations proposed by Baker [3] it is unique. Whereas transitional vacuole models do their best to hide boundary effects, all the new physics in our model arises from the transitioning of one regime to the other. We stress that it requires no parameters beyond the existing Schwarzschild and FLRW metrics.
Categories: astro-ph.CO