Measurements of the Low-Acceleration Gravitational Anomaly from the Normalized Velocity Profile of Gaia Wide Binary Stars and Statistical Testing of Newtonian and Milgromian Theories
Kyu-Hyun Chae
备注：
27 figures, 4 tables, minor revision to match the version published in ApJ
Low-acceleration gravitational anomaly is investigated with a new method of exploiting the normalized velocity profile $\tilde{v}\equiv v_p/v_c$ of wide binary stars as a function of the normalized sky-projected radius $s/r_{\rm{M}}$ where $v_p$ is the sky-projected relative velocity between the pair, $v_c$ is the Newtonian circular velocity at the sky-projected separation $s$, and $r_{\rm{M}}$ is the MOND radius. With a Monte Carlo method Gaia observed binaries and their virtual Newtonian counterparts are probabilistically distributed on the $s/r_{\rm{M}}$ versus $\tilde{v}$ plane and a logarithmic velocity ratio parameter $Γ$ is measured in the bins of $s/r_{\rm{M}}$. With three samples of binaries covering a broad range in size, data quality, and implied fraction of hierarchical systems including a new sample of 6389 binaries selected with accurate distances and radial velocities, I find a unanimous systematic variation from the Newtonian flat line. With $Γ=0$ at $s/r_{\rm{M}}\lesssim 0.15$ or $s\lesssim 1$~kilo astronomical units (kau), I get $Γ=0.068\pm 0.015$ (stat) $_{-0.015}^{+0.024}$ (syst) for $s/r_{\rm{M}} \gtrsim 0.7$ or $s\gtrsim 5$~kau. The gravitational anomaly (i.e.\ acceleration boost) factor given by $γ_g = 10^{2Γ}$ is measured to be $γ_g = 1.37_{-0.09}^{+0.10}$ (stat) $_{-0.09}^{+0.16}$ (syst). With a reduced $χ^2$ test of Newtonian and Milgromian nonrelativistic theories, I find that Newtonian gravity is ruled out at $5.8σ$ ($χ^2_ν=9.4$) by the new sample (and $9.2σ$ by the largest sample used). The Milgromian AQUAL theory is acceptable with $0.5\lesssim χ^2_ν\lesssim 3.1$. These results agree well with earlier results with the "acceleration-plane analysis" for a variety of samples and the "stacked velocity profile analysis" for a pure binary sample.
This document describes the general process of setting up, running, and analysing disc galaxy simulations using the freely available program Phantom of RAMSES (PoR). This implements Milgromian Dynamics (MOND) with a patch to the RAMSES grid-based $N$-body and hydrodynamical code that uses adaptive mesh refinement. We discuss the procedure of setting up isolated and interacting disc galaxy initial conditions for PoR, running the simulations, and analysing the results. This manual also concisely documents all previously developed MOND simulation codes and the results obtained with them.
We study the kinematics of stars in clusters undergoing gas expulsion in standard Newtonian dynamics and also in Milgromian dynamics (MOND). Gas expulsion can explain the observed line-of-sight (LoS) velocity dispersion profile of NGC 2419 in Newtonian dynamics. For a given star formation efficiency (SFE), the shapes of the velocity dispersion profiles, which are normalised by the velocity dispersion at the projected half-mass radius, are almost indistinguishable for different SFE models in Newtonian dynamics. The velocity dispersion of a star cluster in the outer halo of a galaxy can indeed h…
The Kennicutt-Schmidt law is an empirical relation between the star formation rate surface density ($Σ_{SFR}$) and the gas surface density ($Σ_{gas}$) in disc galaxies. The relation has a power-law form $Σ_{SFR} \propto Σ_{gas}^n$. Assuming that star formation results from gravitational collapse of the interstellar medium, $Σ_{SFR}$ can be determined by dividing $Σ_{gas}$ by the local free-fall time $t_{ff}$. The formulation of $t_{ff}$ yields the relation between $Σ_{SFR}$ and $Σ_{gas}$, assuming that a constant fraction ($\varepsilon_{SFE}$) of gas is converted into stars every $t_{ff}$. Thi…
A central problem of contemporary physics is whether the law of gravity is non-Newtonian on galaxy scales. Rodrigues et al. argue that Milgromian gravitation, which solves the flat rotation curve problem without the need for dark matter particles, is ruled out at > 10σ significance. To a large extent, this conclusion relies on galaxies with very uncertain distances and/or nearly edge-on orientations, where dust obscuration often becomes significant. Applying appropriate quality cuts to the data leaves only a handful of outliers to the predictions of Milgromian gravitation according to the anal…
I consider a sample of eight pressure-supported low-surface brightness galaxies in terms of Milgrom's modified Newtonian dynamics (MOND). These objects include seven nearby dwarf spheroidal galaxies -- Sextans, Carina, Leo II, Sculptor, Draco, Leo I, Fornax, and the ultra-diffuse galaxy DF44. The objects are modelled as Milgromian isotropic isothermal spheres characterised by two parameters that are constrained by observations: the constant line-of-sight velocity dispersion and the central surface density. The velocity dispersion determines the total mass, and, with the implied mass-to-light r…
After their birth a significant fraction of all stars pass through the tidal threshold (prah) of their cluster of origin into the classical tidal tails. The asymmetry between the number of stars in the leading and trailing tails tests gravitational theory. All five open clusters with tail data (Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, NGC 752) have visibly more stars within dcl = 50 pc of their centre in their leading than their trailing tail. Using the Jerabkova-compact-convergent-point (CCP) method, the extended tails have been mapped out for four nearby 600-2000 Myr old open clusters…
Unlike Newtonian dynamics which is linear and obeys the strong equivalence principle, in any nonlinear gravitation such as Milgromian dynamics (MOND), the strong version of the equivalence principle is violated and the gravitational dynamics of a system is influenced by the external gravitational field in which it is embedded. This so called External Field Effect (EFE) is one of the important implications of MOND and provides a special context to test Milgromian dynamics. Here, we study the rotation curves (RCs) of 18 spiral galaxies and find that their shapes constrain the EFE. We show that t…
Strong constraints on the gravitational law from $Gaia$ DR3 wide binaries
Scottish Universities Physics Alliance, University of Saint Andrews（圣安德鲁斯大学）；The School of Physical and Chemical Sciences, Queen Mary University of London（伦敦大学玛丽女王学院）；Université de Strasbourg, CNRS UMR 7550, Observatoire astronomique de Strasbourg（斯特拉斯堡大学）；European Southern Observatory（欧洲南方天文台）
Under Newtonian dynamics, the relative motion of the components of a binary star should follow a Keplerian scaling with separation. Once orientation effects and a distribution of ellipticities are accounted for, dynamical evolution can be modelled to include the effects of Galactic tides and stellar mass perturbers, over the lifetime of the solar neighbourhood. This furnishes a prediction for the relative velocity between the components of a binary and their projected separation. Taking a carefully selected small sample of 81 solar neighbourhood wide binaries from the {\it Hipparcos} catalogue…
Relativistic models of light propagation adopted for high-precision astrometry are based on the parametrised post-Newtonian formalism, which provides a framework for examining the effects of a hypothetical violation of general relativity on astrometric data. Astrometric observations are strongly affected by the post-Newtonian parameter $γ$ describing the strength of gravitational light deflection. We study both analytically and numerically how a deviation in the PPN parameter $γ$ from unity, which is the value predicted by general relativity, affects the parallax estimations in Gaia-like astro…
Several recent studies have shown that velocity differences of very wide binary stars, measured to high precision with GAIA, can potentially provide an interesting test for modified-gravity theories which attempt to emulate dark matter. These systems should be entirely Newtonian according to standard dark-matter theories, while the predictions for MOND-like theories are distinctly different, if the various observational issues can be overcome. Here we provide an updated version of our 2019 study using the recent GAIA EDR3 data release: we select a large sample of 73 159 candidate wide binary s…
Several recent studies have shown that very wide binary stars can potentially provide an interesting test for modified-gravity theories which attempt to emulate dark matter; these systems should be almost Newtonian according to standard dark-matter theories, while the predictions for MOND-like theories are distinctly different, if the various observational issues can be overcome. Here we explore an observational application of the test from the recent GAIA DR2 data release: we select a large sample of $\sim 24,000$ candidate wide binary stars with distance $< 200$ parsec and magnitudes $G < 16…
Recent statistical deconvolution methods have produced extended kinematical maps in a range of heliocentric distances that are a factor of two to three larger than those analysed in the Gaia Collaboration based on the same data. In this paper, we use such maps to derive the rotation curve both in the Galactic plane and in off-plane regions and to analyse the density distribution. By assuming stationary equilibrium and axisymmetry, we used the Jeans equation to derive the rotation curve. Then we fit it with density models that include both dark matter and predictions of the MOND (Modified Newto…
Using the recent GAIA eDR3 catalogue we construct a sample of solar neighbourhood isolated wide binaries satisfying a series of strict signal-to-noise data cuts, exclusion of random association criteria and detailed colour-magnitude diagram selections, to minimise the presence of any kinematic contaminating effects having been discussed in the literature to date. Our final high-purity sample consists of 423 binary pairs within 130 pc of the sun and in all cases high-quality GAIA single-stellar fits for both components of each binary (final average RUWE values of 0.99), both also restricted to …
The Doppler effect is commonly used to infer the velocity difference between stars based on the relative shifts in the rest-frame wavelengths of their spectral features. In wide binaries, the difference in gravitational redshift from the surfaces of the constituent stars with distinct compactness dominates at separations above 0.01 pc. I suggest that this effect became apparent for wide pairs in the Gaia eDR3 catalogue but incorrectly interpreted as a possible modification of Newtonian gravity in the internal kinematics of very wide binaries.
The observed flat rotation curves of galaxies are among a number of astrophysical phenomena which require a larger acceleration than can be provided by the Newtonian gravity of the detected baryons. The main proposed solutions are additional undetected mass in the form of dark matter, or a low-acceleration modification to Newtonian gravity known as Milgromian dynamics (MOND). It is possible to directly test MOND using wide binary stars in the Solar neighbourhood, as these systems should contain a dynamically insignificant amount of dark matter even if it comprises most of the Galaxy. However, …
Wide binaries without viable bound Newtonian orbits
INAF, Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所，阿切尔菲天文台）；Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理学研究所）；ESO（欧洲南方天文台）；Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze（佛罗伦萨大学物理与天文学系）；Dipartimento di Fisica e Astronomia, Università degli studi di Padova（帕多瓦大学物理与天文学系）；INAF, Osservatorio Astronomico di Padova（意大利国家天体物理研究所，帕多瓦天文台）；Landessternwarte Zentrum für Astronomie der Universität Heidelberg（海德堡大学州立天文台天文学中心）；Centre for Astrophysics and Supercomputing, Swinburne University of Technology（斯威本科技大学天体物理与超算中心）；Departamento de Fisica, Universidade Federal do Rio Grande do Norte（北里奥格兰德联邦大学物理系）；Instituto de Astrofísica, Pontificia Universidad Católica de Chile（智利天主教大学天体物理研究所）
A Quality Framework for Testing Gravity with Wide Binaries: No Evidence for MOND
University of Portsmouth（朴茨茅斯大学）；California Institute of Technology（加州理工学院）；Queen Mary University of London（伦敦大学玛丽女王学院）；Leiden University（莱顿大学）；University of Cambridge（剑桥大学）
Kinematically cold tidal streams of globular clusters (GC) are excellent tracers of the Galactic gravitational potential at moderate Galactocentric distances, and can also be used as probes of the law of gravity on Galactic scales. Here, we compare for the first time the generation of such streams in Newtonian and Milgromian gravity (MOND). We first compute analytical results to investigate the expected shape of the GC gravitational potential in both frameworks, and we then run N-body simulations with the Phantom of Ramses code. We find that the GCs tend to become lopsided in MOND. This is a c…
We examine the distribution of on-sky relative velocities for wide binaries previously assembled from GAIA DR2 data and focus on the origin of the high velocity tail of apparently unbound systems which may be interpreted as evidence for non-Newtonian gravity in the weak field limit. We argue that this tail is instead explicable in terms of a population of hidden triples, i.e. cases where one of the components of the wide binary is itself a close binary unresolved in the GAIA data. In this case the motion of the photocentre of the inner pair relative to its barycentre affects the apparent relat…
Estimator forensics for the wide-binary gravity test: the eccentricity-triple coupling manufactures a pseudo-signal, and a pre-registered protocol for Gaia DR4
Extremely wide binary stars represent ideal systems to probe Newtonian dynamics in the low acceleration regimes (<10e-10 m/s/s) typical of the external regions of galaxies. Here we present a study of 60 alleged wide binary stars with projected separation ranging from 0.004 to 1 pc, probing gravitational accelerations well below the limit were dark matter or modified dynamics theories set in. Radial velocities with accuracy ~100 m/s were obtained for each star, in order to constrain their orbital velocity, that, together with proper motion data, can distinguish bound from unbound systems. It wa…
Modified Newtonian Dynamics (MOND) at low acceleration has been astonishingly powerful at explaining the flat rotation curve of galaxies and the relation between the baryonic content of the galaxies and their observed circular velocity, known as the Baryonic Tully-Fisher Relationship (BTFR). It is known that MOND fails at explaining the observed velocity dispersion of the ultra-faint dwarf galaxies (UFDs) with the justification that UFDs are more prone to tidal disruption in MOND compared to cold dark matter model. We show that: (i) the ratio of tidal to internal acceleration in UFDs is extrem…
Detection of Gravitational Anomaly at Low Acceleration from a Highest-quality Sample of 36 Wide Binaries with Accurate 3D Velocities
Sejong University（世宗大学）；Korea Astronomy and Space Science Institute（韩国天文与空间科学研究所）；Universidad Nacional Autónoma de México, Instituto de Astronomía（墨西哥国立自治大学天文研究所）；Yonsei University（延世大学）；University of Pittsburgh（匹兹堡大学）
The observed line-of-sight velocity dispersion $σ_{los}$ of the ultra diffuse galaxy Dragonfly 44 (DF44) requires a Newtonian dynamical mass-to-light ratio of $M_{dyn}/L_I=26^{+7}_{-6}$ Solar units. This is well outside the acceptable limits of our stellar population synthesis (SPS) models, which we construct using the integrated galactic initial mass function (IGIMF) theory. Assuming DF44 is in isolation and using Jeans analysis, we calculate $σ_{los}$ profiles of DF44 in Milgromian dynamics (MOND) and modified gravity (MOG) theories without invoking dark matter. Comparing with the observed k…
We consider how the trajectory of an interstellar precursor mission would be affected by the gravity of the Sun in Newtonian and Milgromian dynamics (MOND). The Solar gravity is ${\approx 50\%}$ stronger in MOND beyond a distance of ${\approx 7000}$ astronomical units, the MOND radius of the Sun. A spacecraft travelling at $0.01 \, c$ reaches this distance after 11.1 years. We show that the extra gravity in MOND causes an anomalous deceleration that reduces its radial velocity by ${\approx 3}$ cm/s and the two-way light travel time from the inner Solar System by ${\approx 0.1}$ seconds after 2…
Recent studies have shown that velocity differences of very wide binary stars, measured to high precision with GAIA, can provide an interesting test for modified-gravity theories which emulate dark matter; in essence, MOND-like theories (with external field effect included) predict that wide binaries (wider than ~ 7 kAU) should orbit ~ 15% faster than Newtonian for similar orbits; such a shift is readily detectable in principle in the sample of 9,000 candidate systems selected from GAIA EDR3 by Pittordis and Sutherland (2022; PS22). However, the main obstacle at present is the observed "fat ta…
Stellar-mass black holes in young massive and open stellar clusters -- VII. Comparisons with gravitational-wave events until LVK-O4a and Gaia compact binaries
Helmholtz-Instituts für Strahlen- und Kernphysik (HISKP)（亥姆霍兹射线与核物理研究所）
We describe how a simple class of out of equilibrium, rotating and asymmetrical mass distributions evolve under their self-gravity to produce a quasi-planar spiral structure surrounding a virialized core, qualitatively resembling a spiral galaxy. The spiral structure is transient, but can survive tens of dynamical times, and further reproduces qualitatively noted features of spiral galaxies as the predominance of trailing two-armed spirals and large pitch angles. As our models are highly idealized, a detailed comparison with observations is not appropriate, but generic features of the velocity…
