New Preprint on Wide Binaries Supports MOND

[ohwilleke]

TL;DR Summary

Wide binary stars have weak enough gravitational fields to enter the MOND regime, and a paper looking at new better data on them supports this hypothesis.

In a dark matter hypothesis, wide binary stars should exhibit no dark matter phenomena since dark matter halos are so much bigger than pairs of distant gravitationally bound pairs of stars. But, in a MOND hypothesis, wide binary stars should be more strongly bound to each other than Newtonian gravity would predict.

GAIA's latest edition has greatly improved the quality of the data on wide binary star systems allowing these hypotheses to be compared to observations.

A paper looking at new data sees a MOND effect in wide binary stars. The discussion engages with possible sources of noise or bias in the results that have been proposed in connection with earlier wide binary data, and finds those hypotheses to be implausible at best.

The Gaia eDR3 catalogue has recently been used to construct samples of nearby wide binaries to study the internal kinematics of these objects using relative velocities of the two component stars, ΔV, total binary masses, mB, and separations, s. For s≳0.035 pc, these binaries probe the low acceleration a<a(0) regime over which the gravitational anomalies usually attributed to dark matter are observed in the flat rotation curves of spiral galaxies, where a(0)≈1.2×10^10 is the acceleration scale of MOND.

Such experiments test the degree of generality of these anomalies, by exploring the same acceleration regime using independent astronomical systems of vastly smaller mass and size. A signal above Newtonian expectations has been observed when a<a(0), alternatively interpreted as evidence of a modification in the relevant fundamental physics, or as being due to kinematic contaminants affecting the experiment; the presence of undetected stellar components, unbound encounters and spurious projection effects.

Here I take advantage of the enhanced DR3 Gaia catalogue to perform a more rigorous and detailed study of the internal kinematics of wide binaries than what has previously been possible. Having internally determined accurate Gaia stellar masses and estimates of binary probabilities for each star using spectroscopic information, together with a larger sample of radial velocities, allows for a significant improvement in the analysis of wide binaries and careful exclusion of possible kinematic contaminants. Resulting ΔV vs. s and ΔV vs. mB scalings accurately tracing Newtonian expectations for the high acceleration regime, but consistent with the distance and mass velocity scalings observed in spiral galaxies in the low acceleration one, are obtained.

X. Hernandez, "Internal kinematics of GAIA DR3 wide binaries: anomalous behaviour in the low acceleration regime" arXiv:2304.07322 (April 14, 2023).

 

[Dragrath]

Interesting MOND is really gaining ground on the evidence side of things these days the main issue MOND has is explaining why gravity's strength relationship with distance changes as MOND remains purely an observational theory. Will still probably take a long time to become more accepted with the main hurdle likely being the lack of an accepted mechanism.
I have come to suspect that finding a path towards quantum gravity will likely be required before we can get at the why.

The most promising lead for me is the falsification of the cosmological principal via comparing the CMB dipole to a dipole of cosmologically distant sources as that result now appears to have reached a five sigma discrepancy from what would be required for the cosmological principal to be valid in our Universe. In published work this is "only" 4.9 sigma discrepancy but if a preprint from December shows promise in its independent verification of the results then we can raise the significance to 5.7 sigma

https://iopscience.iop.org/article/10.3847/2041-8213/abdd40

This naturally would force us to adopt inhomogeneous and anisotropic cosmology leading to the large scale inhomogenous and anisotropic cosmology that the No big crunch theorem tells us not only automatically resolves dark energy as being the demonstrably irreducible asymmetric components from the metric tensor in the large scale limit (space much larger than the speed of causality) of the Einstein field equations. If this is the case then there would likely have to be a minimum nonzero contribution to the overall metric for any piece of information from its initial conditions at least in the case of off diagonal contributions. If this also applies to linear terms then would that not result in a additional nonlocal component of gravity which would depending on distance and size of the universe start to become significant at some particular distance where the two contributions are equal in magnitude. Would this not reproduce MOND type behavior within the unconstrained nonlinear Einstein field equations ultimately as a side effect of conserving information of the initial conditions? Given that this is the inhomogeneous and anisotropic large scale(limit of size goes to infinity) a.k.a. nonlinear domain of the full Einstein field equations. https://iopscience.iop.org/article/10.1088/1475-7516/2016/10/022/meta

Given that these equations have been continuously supported by experiments should we not taken a deeper look into this domain even if it is only able to be solved numerically? The same is true of other systems of multivariate differential equations in physics after all.Also I can't help but notice the formalism of the proof by Matthew Kleban and Leonardo Senatore in 2016 is suspiciously analogous to the second law of thermodynamics only with volume rather than entropy. Entropy naturally suggests a link to information which given that the context of the proof is showing that there are no internally self consistent metrics possible which allow an overall slowing nor reversal, (basically information theory) it suggests our normal models in cosmology violate conservation of information in ways which are causally forbidden.

Oh and this theorem also comes with the added benefit of coupling large scale properties of the overall metric to local ones thus simultaneously satisfying Bell's inequality. Mathematically as far as I can tell from the paper these nonlocal effects relate to the advancing of the past light cone carrying information away from any particular event it suggests a nonlocal coupling arising from the affects of expansion under unequal passage of time in warped spacetime. At the very least it falsifies the idea that just because the expansion was fairly homogeneous and isotropic in the past doesn't mean it would stay that way.

 

[timmdeeg]

Hence, the results presented here can not presently be compared to the majority of existing modified gravity/modified inertia proposals.

And aren't consistent with Dark Matter neither. So perhaps with field self-interaction?

 

[Vanadium 50]

I read the paper. I do not think it is very good: I would have expected a plot of something close to measured on it, with two curved: the Newtonian and MOND predictions, showing what the data scatter is and how well it fits each hypothesis. (The "money plot") This is particularly important with such highly selected and processed data.

As I understand it, it's actually evidence against MOND.

The sun is in a moderately MONDy orbit in the galaxy: acceleration is near 1.5 a0. So these binaries will have the galactic gravity on top of the local gravity, and the magnitudes will be comparable 0 but more "deep Newtonian" than "deep MOND". So the effect must be both diluted and depend on the orientation of these stars with respect to the galactic center. Where is this taken into account? Integrating over the effect will wash it out.

In short you do not expect MONDy behavior from bound star systems in our galactic neighborhood.

 

[ohwilleke]

I read the paper. I do not think it is very good: I would have expected a plot of something close to measured on it, with two curved: the Newtonian and MOND predictions, showing what the data scatter is and how well it fits each hypothesis. (The "money plot") This is particularly important with such highly selected and processed data.

As I understand it, it's actually evidence against MOND.

The sun is in a moderately MONDy orbit in the galaxy: acceleration is near 1.5 a0. So these binaries will have the galactic gravity on top of the local gravity, and the magnitudes will be comparable 0 but more "deep Newtonian" than "deep MOND". So the effect must be both diluted and depend on the orientation of these stars with respect to the galactic center. Where is this taken into account? Integrating over the effect will wash it out.

In short you do not expect MONDy behavior from bound star systems in our galactic neighborhood.

You could be right about the external field effect issue, although it depends upon how the wide binaries in the sample are selected.

I don't disagree that the charts in the paper could have been prepared to be more clear. The strength of the effect isn't very well quantified in sigmas compared to the null hypothesis of Newtonian gravity.

On the other hand, the analysis ruling out the confounds claimed in other recent papers on wide binaries which I've also read, appears solid.

Of course, the observation of a significant effect requires some non-DM explanation, even if MOND is not the right answer. Wide binaries are a good testing ground for distinguishing non-DM explanations of phenomena often attributed to dark matter.

FWIW, Deur's gravitational self-interaction unlike MOND would also not predict this effect (based upon back of napkin calculations) even in the absence of a confounding external field effect.

 

[strangerep]

the main issue MOND has is explaining why gravity's strength relationship with distance changes [...]

The observations show dependence on an acceleration scale, not a distance scale. Hence MOND's universal $a_0$ constant.

 

[ohwilleke]

Another new wide binary paper makes a strong claim.

A new preprint claims to observe at ten sigma significance, a deviation from Newtonian gravity consistent with MOND in wide binary stars from a sample of 26,615 stars and also appears to consider the external field effect of MOND, which is a concern previously raised about wide binary star gravitational evidence. Previous papers by other authors have questioned whether the data quality supports this conclusion.

This would be contrary to the expectations of dark matter phenomena coming from a halo of dark matter particles and would also be contrary to Deur's gravitational field self-interaction paradigm.

The abstract and paper are as follows:

A gravitational anomaly is found at weak gravitational acceleration g(N)<10⁻⁹ m s^-2

from analyses of the dynamics of wide binary stars selected from the Gaia EDR3 database that have accurate distances, proper motions, and reliably inferred stellar masses.

Implicit high-order multiplicities are required and the multiplicity fraction is calibrated so that binary internal motions agree statistically with Newtonian dynamics at a high enough acceleration of 10⁻⁸ m s⁻². The observed sky-projected motions and separation are deprojected to the three-dimensional relative velocity v and separation r through a Monte Carlo method, and a statistical relation between the Newtonian acceleration g(N)≡GM/r² (where M is the total mass of the binary system) and a kinematic acceleration g≡v²/r is compared with the corresponding relation predicted by Newtonian dynamics.

The empirical acceleration relation at <10⁻⁹ m s⁻² systematically deviates from the Newtonian expectation. A gravitational anomaly parameter δ(obs−newt) between the observed acceleration at g(N) and the Newtonian prediction is measured to be: δ(obs−newt)=0.034±0.007 and 0.109±0.013 at g(N)≈10^−8.91 and 10^−10.15 m s⁻², from the main sample of 26,615 wide binaries within 200 pc. These two deviations in the same direction represent a 10σ significance.

The deviation represents a direct evidence for the breakdown of standard gravity at weak acceleration. At g(N)=10^−10.15 m s⁻², the observed to Newton predicted acceleration ratio is g(obs)/g(pred)=10^{2√δ(obs−newt)}=1.43±0.06. This systematic deviation agrees with the boost factor that the AQUAL theory predicts for kinematic accelerations in circular orbits under the Galactic external field.

Kyu-Hyun Chae, "Breakdown of the Newton-Einstein Standard Gravity at Low Acceleration in Internal Dynamics of Wide Binary Stars" arXiv:2305.04613 (May 8, 2023) (submitted to Apj).

 

[ohwilleke]

Commentary from Stacy McGaugh https://tritonstation.com/2023/05/18/wide-binary-weirdness/

A snippet:

"One of the first papers to address this is Hernandez et al (2022). They found a boost in speed that looks like MOND but is not MOND. Rather, it is consistent with the larger speed that is predicted by MOND in the absence of the EFE. This implies that the radial acceleration relation depicted above is absolute, and somehow more fundamental than MOND. This would require a new theory that is very similar to MOND but lacks the EFE, which seems necessary in other situations. Weird.

A thorough study has independently been made by Pittordis & Sutherland (2023). I heard a talk by them over Zoom that motivated the previous post to set the stage for this one. They identify a huge sample of over 73,000 wide binaries within 300 pc of the sun. Contrary to Hernandez et al., they find no boost at all. The motions of binaries appear to remain perfectly Keplerian. There is no hint of MOND-like effects. Different.

OK, so that is pretty strong evidence against MOND, as Indranil Banik was describing to me at the IAU meeting in Potsdam, which is why I knew to tune in for the talk by Pittordis. But before I could write this post, yet another paper appeared. This preprint by Kyu-Hyun Chae splits the difference. It finds a clear excess over the Newtonian expectation that is formally highly significant. It is also about right for what is expected in MOND with the EFE, in particular with the AQUAL flavor of MOND developed by Bekenstein & Milgrom (1984).

So we have one estimate that is MOND-like but too much for MOND, one estimate that is straight-laced Newton, and one estimate that is so MOND that it can start to discern flavors of MOND.

I really don’t know what to make of all this."

 

[kodama]

Commentary from Stacy McGaugh https://tritonstation.com/2023/05/18/wide-binary-weirdness/

A snippet:

"One of the first papers to address this is Hernandez et al (2022). They found a boost in speed that looks like MOND but is not MOND. Rather, it is consistent with the larger speed that is predicted by MOND in the absence of the EFE. This implies that the radial acceleration relation depicted above is absolute, and somehow more fundamental than MOND. This would require a new theory that is very similar to MOND but lacks the EFE, which seems necessary in other situations. Weird.

A thorough study has independently been made by Pittordis & Sutherland (2023). I heard a talk by them over Zoom that motivated the previous post to set the stage for this one. They identify a huge sample of over 73,000 wide binaries within 300 pc of the sun. Contrary to Hernandez et al., they find no boost at all. The motions of binaries appear to remain perfectly Keplerian. There is no hint of MOND-like effects. Different.

OK, so that is pretty strong evidence against MOND, as Indranil Banik was describing to me at the IAU meeting in Potsdam, which is why I knew to tune in for the talk by Pittordis. But before I could write this post, yet another paper appeared. This preprint by Kyu-Hyun Chae splits the difference. It finds a clear excess over the Newtonian expectation that is formally highly significant. It is also about right for what is expected in MOND with the EFE, in particular with the AQUAL flavor of MOND developed by Bekenstein & Milgrom (1984).

So we have one estimate that is MOND-like but too much for MOND, one estimate that is straight-laced Newton, and one estimate that is so MOND that it can start to discern flavors of MOND.

I really don’t know what to make of all this."

more research is needed

 

[ohwilleke]

McGaugh reports on the public social media published communications of the respective authors of the papers with each other. https://tritonstation.com/2023/05/19/commentary-on-wide-binaries/

The critical author thinks that the sample selection leads to the discrepancy. The latest author disputes that argument.

 

[Madeleine Birchfield]

Marcel Pawlowski has a twitter thread about wide binaries and the discrepancies between the Chae et al and Banik et al results:

 

[Sagittarius A-Star]

Another new wide binary paper makes a strong claim.

A new preprint claims
...
Kyu-Hyun Chae, "Breakdown of the Newton-Einstein Standard Gravity at Low Acceleration in Internal Dynamics of Wide Binary Stars" arXiv:2305.04613 (May 8, 2023) (submitted to Apj).

Here is a publication of this paper:
https://iopscience.iop.org/article/10.3847/1538-4357/ace101

 

[AndreasC]

Apparently Indranil Banik et al will release a paper that is supposed to show MOND is in strong conflict with the wide binary data, and explain what the mistake of the Chae paper was. It is also interesting that Banik up until this point argued strongly in favor of MOND. It's all very weird how research papers arguing for every possible position have appeared, maybe we just need better data... But I know almost nothing about astrophysics so I can't have an opinion.

 

[Vanadium 50]

will release a paper

Doesn't it make more sense to discuss this after the paper comes out?

 

[AndreasC]

Doesn't it make more sense to discuss this after the paper comes out?

Yep. I'm just mentioning it as "news". Also he has released this video:



...and a talk at a MOND conference. It will be interesting to see what they find. In the comments of that video Banik expresses his opinion on why he thinks the Chae paper is wrong, and you can also see Chae's reply. However that was before they both met at the MOND conference, although according to McGaugh's blog there wasn't exactly consensus. We'll have to wait and see the publications.