On the tension between the Radial Acceleration Relation and Solar System quadrupole in modified gravity MOND
arxiv(2024)
摘要
Modified Newtonian Dynamics (MOND), postulating a breakdown of Newtonian
mechanics at low accelerations, has considerable success at explaining galaxy
kinematics. However, the quadrupole of the gravitational field of the Solar
System (SS) provides a strong constraint on the way in which Newtonian gravity
can be modified. In this paper we assess the extent to which the AQUAL and
QUMOND modified gravity formulations of MOND are capable of accounting
simultaneously for the Radial Acceleration Relation (RAR), the Cassini
measurement of the SS quadrupole and the kinematics of wide binaries in the
Solar neighbourhood. We achieve this by inferring the location and sharpness of
the MOND transition from the SPARC RAR under broad assumptions for the
behaviour of the interpolating function and external field effect. We constrain
the same quantities from the SS quadrupole, finding that this requires a
significantly sharper transition between the deep-MOND and Newtonian regimes
than is allowed by the RAR (an 8.7σ tension under fiducial model
assumptions). This may be relieved somewhat by allowing additional freedom in
galaxies' mass-to-light ratios – which also improves the RAR fit – and more
significantly (to 1.9σ) by removing galaxies with bulges. For the first
time, we also apply to the SPARC RAR fit an AQUAL correction for flattened
systems, obtaining similar results. Finally we show that the SS quadrupole
constraint implies, to high precision, no deviation from Newtonian gravity in
nearby wide binaries, and speculate on possible resolutions of this tension
between SS and galaxy data within the MOND paradigm.
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