An eccentric transit timing test of modified gravity

TL;DR

This paper proposes using precise measurements of apsidal precession in eclipsing binaries to test modified gravity theories like MOND, which predict unique orbital effects absent in Newtonian gravity, potentially providing a solar-system-like test at galactic distances.

Contribution

It introduces a novel method to test MOND's external field effect through transit timing and duration variations in eclipsing binaries, bypassing Solar System limitations.

Findings

Apsidal precession differs under MOND compared to Newtonian gravity.

Transit timing variations can reveal MOND effects in suitable binaries.

Potential for a definitive test of MOND theories with current observational techniques.

Abstract

The MOND modified gravity paradigm, best known for its agreement with galactic rotation curve data, is difficult to devise laboratory tests for. MOND's predictions differ substantially from Newtonian gravity only in the case of very small accelerations ($a < a_0 = 1.2\times10^{-10}~\mathrm{m/s}^2 = 3.8~\mathrm{mm/s/y}$). In the solar system, radio and laser measurements of test bodies do permit acceleration measurements this precise; however, in at least some viable realizations, MOND has an "external field effect" (EFE) which essentially disables the MOND effects in the presence of the inner Milky Way's background gravitational field, invalidating Solar System limits. Can we do any measurement with Solar-System-like acceleration precision, but on a system many kiloparsecs away that avoids the EFE? In this paper, we show that MOND's non-$1/r^2$ gravitational acceleration has a unique and hard-to-fake effect: in contrast to the non-precessing elliptical orbits predicted by two-body Newtonian gravity, in the presence of MOND we expect apsidal precession in two-body systems. An extreme precision apsidal precession detection opportunity is available for eclipsing binaries, where, for some viewing geometries, apsidal precession causes transit time variations (TTVs) and transit duration variations (TDVs). If appropriate binaries can be found and measured, the presence or absence of timing variations may provide a definitive "solar-system-like" test of many EFE-bearing MOND theories like QUMOND.