Neither the astrophysicists who say that there is evidence of MOND in wide binaries, nor those who say there is not, are relenting, and I currently rate the debate as inconclusive.
If this paper is right, it is bad for MOND, but good for Deur, who reproduces MOND behavior in galaxies by another formula and mechanism.
Wide binaries (WBs) offer a unique opportunity to test gravity in the low-acceleration regime, where modifications such as Milgromian dynamics (MOND) predict measurable deviations from Newtonian gravity.
We construct a rigorous framework for conducting the wide binary test (WBT), emphasizing high quality sample selection, filtering of poor astrometric solutions, contamination mitigation, and uncertainty propagation. We show that undetected close binaries, chance alignments, and improper treatment of projection effects can mimic MOND-like signals. We introduce a checklist of best practices to identify and avoid these pitfalls. Applying this framework to Gaia DR3 data, we compile a high-purity sample of WBs within 130 pc with projected separations of 1 - 30 kAU, spanning the transition between the Newtonian and MOND regimes.
We find that the scaled relative velocity distribution of wide binaries does not exhibit the 20% enhancement expected from MOND and is consistent with Newtonian gravity across all separations. A meta-analysis of previous WBTs shows that apparent MOND signals diminish as methodological rigour improves. We conclude that when stringent quality controls are applied, there is no observational evidence for MOND-induced velocity boosts in wide binaries.
Our results place strong empirical constraints on modified gravity theories operating between a0/10 and 200 a0, where a0 is the MOND acceleration scale. Across this range of internal accelerations, Newtonian gravity is up to 1500x more likely than MOND for our cleanest sample.
Stephen A. Cookson, Indranil Banik, Kareem El-Badry, Will Sutherland, Zephyr Penoyre, Charalambos Pittordis, Cathie J. Clarke, "A Quality Framework for Testing Gravity with Wide Binaries: No Evidence for MOND" arXiv:2602.24035 (February 27, 2026) (published in MNRAS).
7 comments:
Link back to the latest paper by the other side.
https://dispatchesfromturtleisland.blogspot.com/2026/01/gravity-anomalies-seen-in-wide-binary.html
Indeed.
In that thread, I link to where Stacy McGaugh made his own judgment about who was right. At the time he picked Hernandez, who like Chae claimed evidence for MOND, but more cautiously and with a cleaner sample. Now Chae and Hernandez are on the same team. Meanwhile Banik is also still insisting no MOND... I think that the principles McGaugh uses in his original post, should still be applicable. If you drill down into the details, there is a common set of observational facts, and all these papers pick a subset of those facts and then analyze them using distinct criteria.
Do you have any thoughts (from a legal perspective) on the epistemology of resolving such a situation, where contradictory claims are derived from the same overall body of evidence?
As is remarked by the 1st paper it only takes one good example to disprove a theory. Let's assume in the follow-up volleys both sides can point to a exquisitely precise example that disproves the others' theory. Sometimes Newton, sometimes MOND. What's the synthesis?
In the legal world, battles of experts are resolved by panels of ordinary people called juries, so we don't have much of an epistemology for resolving them. I see the merit in both approaches taken and I am very on the fence.
"As is remarked by the 1st paper it only takes one good example to disprove a theory. Let's assume in the follow-up volleys both sides can point to a exquisitely precise example that disproves the others' theory. Sometimes Newton, sometimes MOND. What's the synthesis?"
First off, the big problem on both sides is that the data has lots of potential systemic error, mostly from apparent wide binary systems that are actually bound systems of three or more stars with the stars in excess of the apparent pair being hard to resolve with the telescope instrumentation and angles of observation used. The anti-MOND analysis uses global comparisons of apparent wide binary behavior charted against observation quality to make that argument.
Closely related is analysis error. Another recent paper outside the wide binary debate but looking at clusters of stars within the Milky Way suggests that because the Milky Way is not homogeneous, that there may be pockets of sub a0 gravitational field regions where MOND applies (because the external field effect does not) at radii from the galactic center where simpler assumptions about the local gravitational field and external field effects would assume that the external field should eliminate MOND effects. In a liminal area like the one that these papers are exploring, a modest amount of inhomogeneity could account for seemingly inconsistent results, and both sides are using very simple external field is a function of distance from the galactic center models, in a sample that is likely to be large enough for inhomogeneity to matter. This is not something that any of the wide binary papers has really considered seriously.
Second, MOND is only is mini-family within a larger macro-family lots of modified gravity/modified inertia/reanalyzed gravity theories, so if simple toy-model MOND doesn't work, one possible conclusion is that another theory in that family of theories works better. For example, toy-model MOND and Deur's approach make opposite predictions about wide binaries, despite making identical predictions at galactic scales for galaxy sized systems as a whole.
Third, any pockets of MOND-like behavior are generically a big problem for dark matter particle theories.
The paper I'm referring to re analysis error is discussed at https://dispatchesfromturtleisland.blogspot.com/2026/03/mond-like-behavior-within-milky-way-in.html
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