Efforts to determine is wide binary star systems show a change in gravitational acceleration at Newtonian accelerations below Milgrom's constant, as predicted by MOND (but not generically by all modified gravity explanations of dark matter phenomena) have had mixed and contradictory results. The latest paper on the subject, a small pilot study using new methods supports the existence of a non-Newtonian gravitational enhancement for wide binaries whose gravitational pull on each other is below Milgrom's constant.
Wide binary tests exclude almost all dark matter particle theories, if they show non-Newtonian gravitational enhancements in weak fields, and also discriminate meaningfully between different gravity based approaches to explain dark matter phenomena if the data allows for sufficiently precise conclusions.
But competing considerations of data quality (e.g., it is easy to mistake a system with more than two stars for a wide binary system if one of the stars is feint or the angle of observation is poor), and data quantity (to give the observations statistical power), make this astronomy test of weak field gravity challenging to extract convincing results from.
When 3D relative displacement r and velocity v between the pair in a gravitationally-bound system are precisely measured, the six measured quantities at one phase can allow elliptical orbit solutions at a given gravitational parameter G. Due to degeneracies between orbital-geometric parameters and G, individual Bayesian inferences and their statistical consolidation are needed to infer G as recently suggested by a Bayesian 3D modeling algorithm.
Here I present a fully general Bayesian algorithm suitable for wide binaries with two (almost) exact sky-projected relative positions (as in the Gaia data release 3) and the other four sufficiently precise quantities. Wide binaries meeting the requirements of the general algorithm to allow for its full potential are rare at present, largely because the measurement uncertainty of the line-of-sight (radial) separation is usually larger than the true separation.
As a pilot study, the algorithm is applied to 32 Gaia binaries for which precise HARPS radial velocities are available. The value of Γ ≡ log(10)√ G/G(N) (where G(N) is Newton's constant) is −0.002 + 0.012 −0.018 supporting Newton for a combination of 24 binaries with Newtonian acceleration g(N) > 10^−9 ms^−2, while it is Γ = 0.063 + 0.058 − 0.047 or 0.134 + 0.050 − 0.040 for 7 or 8 binaries with g(N) < 10^−9 ms^−2 (depending on one system) showing tension with Newton. The Newtonian ``outlier'' is at the boundary set by the Newtonian escape velocity, but can be consistent with modified gravity.
The pilot study demonstrates the potential of the algorithm in measuring gravity at low acceleration with future samples of wide binaries.
Kyu-Hyun Chae, "Bayesian Inference of Gravity through Realistic 3D Modeling of Wide Binary Orbits: General Algorithm and a Pilot Study with HARPS Radial Velocities" arXiv:2508.11996 (August 16, 2025).
3 comments:
Wide binary tests exclude almost all dark matter particle theories, if they show non-Newtonian gravitational enhancements in weak fields,
if these papers stand the test of time, couldn't someone invent a dark matter particle theories that do show non-Newtonian gravitational enhancements in weak fields with some imagination and creativity.
or is it fundamentally impossible for dark matter particle theories to do this, or perhaps there are dark matter that don't involve particles, that can explain wide binaries below ao
@neo It would require something more than just the usual halo of dark matter particles. As McGaugh emphasizes, the usual dark matter models also don't explain why other MONDian phenomenology works (e.g. baryonic Tully-Fisher). There are a handful of dark matter models designed specifically for compatibility with MOND, e.g. Khoury and Berezhiani's superfluid DM or Blanchet's dark dipole DM. One should check if they are capable of explaining MOND effects in wide binaries.
@Mitchell very interesting indeed could Khoury and Berezhiani's superfluid DM or Blanchet's dark dipole DM are capable of explaining MOND effects in wide binaries?
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