From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity

Abstract

Astronomical observations reveal a major deficiency in our understanding of physics − the detectable mass is insufficient to explain the observed motions in a huge variety of systems given our current understanding of gravity, Einstein's General theory of Relativity (GR). This missing gravity problem may indicate a breakdown of GR at low accelerations, as posited by Milgromian dynamics (MOND). We review the MOND theory and its consequences, including in a cosmological context where we advocate a hybrid approach involving light sterile neutrinos to address MOND's cluster-scale issues. We then test the novel predictions of MOND using evidence from galaxies, galaxy groups, galaxy clusters, and the large scale structure of the Universe. We also consider whether the standard cosmological paradigm (ΛCDM) can explain the observations, and review several previously published highly significant falsifications of it. Our overall assessment considers both the extent to which the data agree with each theory and how much flexibility each has when accommodating the data, with the gold standard being a clear a priori prediction not informed by the data in question. We also consider some future tests, including on scales much smaller than galaxies. Our conclusion is that MOND is favoured by a wealth of data across a huge range of astrophysical scales, ranging from the kpc scales of galactic bars to the Gpc scale of the local supervoid and the Hubble tension, which is alleviated in MOND through enhanced cosmic variance.

Overestimated inclinations of Milgromian disc galaxies: the case of the ultradiffuse galaxy AGC 114905

“…The limits in Equation 1follow from a new nonrelativistic gravity theory based on a Lagrangian, thereby respecting the usual conservation laws with respect to linear and angular momentum and the energy (Bekenstein & Milgrom 1984). The generalized non-linear Poisson equation derived from this Lagrangian leads to a rich behaviour of gravitating systems, accounting automatically for hitherto unexplained phenomena like the KBC void and Hubble tension (Haslbauer et al 2020), extreme galaxy cluster collisions at high redshift (Katz et al 2013;Asencio et al 2021), the Local Group satellite planes Bílek et al 2018Bílek et al , 2021, and many others besides while remaining consistent with galaxy cluster dynamics and early Universe observations (for an extensive review, see Banik & Zhao 2022). The MOND Poisson equation can be solved using standard mesh-refinement codes like phantom of ramses (por; Lüghausen et al 2015;Nagesh et al 2021) and raymond (Candlish et al 2015).…”

“…The EFE is a fundamental consequence of MOND that has always been part and parcel of it (see section 3 of Milgrom 1983). Observational evidence for the EFE is discussed further in section 3.3 of Banik & Zhao (2022). Disc galaxies experiencing the strong EFE of a cluster environment can become lopsided (Candlish et al 2018), though even a rather weak EFE can have subtle consequences (Banik et al 2020).…”

“…Thus, even a very isolated galaxy should experience an external field of a few percent of a 0 . If the galaxy has a very low surface density such that Σ0/ΣM 0.05, then the EFE would dominate everywhere, making the galaxy quasi-Newtonian (see section 2.4 of Banik & Zhao 2022). Since the equations of motion in this regime are like those of Newtonian dynamics but with renormalized G, the disc should be unstable for much the same reason that a bare disc is unstable in Newtonian gravity (Hohl 1971).…”

Simplification of Galactic Dynamic Equations

“…One without sharp logic can hardly check the validity of the results or find out where a bug exists. From the review paper [29], we can find a number of studies misled by the model, much of time and resource was wasted by the professional barriers. The simple treatment is feasible for organizing experimental data and laws, but the galactic dynamics and structure involve large scale space-time geometry and partial differential equations of gravity and matter distribution, so it is impossible to obtain profound results by simple formula and conjecture.…”

3D hydrodynamic simulations for the formation of the Local Group satellite planes

“…It is also possible to fit the CMB in MOND without any sterile neutrino component (Skordis & Z lośnik 2021), though it is unclear whether this approach can explain the properties of galaxy clusters. For a recent review of MOND that considers evidence from a wide range of scales and discusses the cosmological aspects in some detail, we refer the reader to Banik & Zhao (2022).…”