2005/11/30 by Hongsheng Zhao, HongSheng Zhao, LanLan Tian +1
Physics and Astronomy · #Astronomy #Astrophysics #Binary star #Cosmology and Gravitation Theories #Dark matter #Dark matter halo #Flattening #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gamma-ray bursts and supernovae #Globular cluster #Halo #Physics #Roche limit #Roche lobe #Stars #astro-ph
paper · pdf · doi:10.1051/0004-6361:20054379
11p, 7 figs, accepted for Astronomy and Astrophysics
arxiv created 2006/02/02 · openalex publication_date 2006/04/13 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Dark Matter (DM) theories and mass-tracing-light theories like MOND are by construction nearly degenerate on galactic scales, but not when it comes to the predicted shapes of Roche Lobes of a two-body system (e.g., a globular cluster orbiting a host galaxy). We show that the flattening of the Roche lobe is sensitive to the function in modification of the law of gravity. We generalise the analytical results obtained in the deep-MOND limit by Zhao (2005), and consider a binary in the framework of a MOND-like gravity modification function or a general non-Keplerian gravity . We give analytical expressions for the inner Lagrange point and Robe lobe axis ratios. The Roche lobe volume is proven to scale linearly with the true mass ratio, which applies to any , hence mass-tracing light models would overpredict the Roche lobe of a DM-poor globular cluster in a DM-rich host galaxy, and underpredict the size of a DM-richer dwarf satellite. The lobes are squashed with the flattening ~0.4 in the strong gravity and ~0.6 in the weak gravity; a precise measurement of the flattening could be used to verify the anisotropic dilation effect which is generic to MOND-like gravity. We generalise these results for extended mass distribution, and compare predicted Roche radii with limiting radii of observed globular clusters and dwarf galaxy satellites.