Roche Lobe Sizes in Deep-MOND Gravity

Abstract

MOdified Newtonian Dynamics (MOND) is evolving from an empirical to a decent theory respecting fundamental physics after Bekenstein (2004) showed that lensing and Hubble expansion can be modeled rigourously in a Modified Relativity. The degeneracy of MOND with Dark Matter can be broken if we examine the non-linear MONDian Poisson's equation in detail. Here we study the effect of tides for a binary stellar system or a baryonic satellite-host galaxy system. We show that the Roche lobe is more squashed than the Newtonian case due to the anisotropic dilation effect in deep-MOND. We prove analytically that the Roche lobe volume scales linearly with the "true" baryonic mass ratio in both Newtonian and deep-MOND regimes, insensitive to the modification to the inertia mass. Hence accurate Roche radii of satellites can break the degeneracy of MOND and dark matter theory. Globular clusters and dwarf galaxies of comparable luminosities and distances show a factor of ten scatter in limiting radii; this is difficult to explain in any "mass-tracing-light" universe. The results here are generalizable to the intermediate MOND regime for a wide class of gravity modification function $\mu (g)$ (Zhao and Tian, astro-ph/0511754).

4 pages, 2 figures, Astronomy and Astrophysics Letter, in press

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• Testing Bekenstein's Relativistic MOND gravity with Lensing Data
• Modelling the Pioneer anomaly as modified inertia
• The distribution and morphologies of Fornax Cluster dwarf galaxies suggest they lack dark matter
• A new formulation of the external field effect in MOND and numerical simulations of ultra-diffuse dwarf galaxies $-$ application to NGC 1052-DF2 and NGC 1052-DF4
• MOND plus classical neutrinos not enough for cluster lensing
• Galactic kinematics with modified Newtonian dynamics
• Roche Lobe Shapes for testing MOND-like Modified Gravity
• Dark Fluid: Towards a unification of empirical theories of galaxy rotation, Inflation and Dark Energy
• The relation between stellar mass and weak lensing signal around galaxies: Implications for MOND
• Probing the radial acceleration relation and the strong equivalence principle with the Coma cluster ultra-diffuse galaxies
• Tidal radii and escape speeds in dwarf spheroidal galaxies under MOND and dark halos compared
• Modified gravity, Dark Energy and MOND
• NGC 2419 does not challenge MOND
• Discussing the first velocity dispersion profile of an ultra-diffuse galaxy in MOND
• Astrophysics in 2006
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• Origin of the spectacular tidal shells of galaxy NGC474
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