Internal kinematics of GAIA DR3 wide binaries: anomalous behaviour in the low acceleration regime

Abstract: The {\it Gaia} eDR3 catalogue has recently been used to study statistically the internal kinematics of wide binary populations using relative velocities of the two component stars, $\Delta V$, total binary masses, $m_{B}$, and separations, $s$. For $s \gtrsim 0.01$ pc, these binaries probe the low acceleration $a \lesssim 2a_{0}$ regime where gravitational anomalies usually attributed to dark matter are observed in the flat rotation curves of spiral galaxies, where $a_{0}\approx 1.2\times 10^{-10}$m s$^{-2}$ 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 $a \lesssim 2a_{0}$, alternatively interpreted as evidence of a modification of gravity, or as due to kinematic contaminants; undetected stellar components, unbound encounters or spurious projection effects. Here I take advantage of the enhanced DR3 {\it Gaia} catalogue to perform a more rigorous study of the internal kinematics of wide binaries than what has previously been possible. Internally determined {\it Gaia} stellar masses and estimates of binary probabilities for each star using spectroscopic information, together with a larger sample of radial velocities, allow for a significant improvement in the analysis and careful exclusion of possible kinematic contaminants. Resulting $\Delta V$ scalings accurately tracing Newtonian expectations for the high acceleration regime, but markedly inconsistent with these expectations in the low acceleration one, are obtained. A non-Newtonian low acceleration phenomenology is thus confirmed.

• The paper analyzes Gaia DR3 wide binaries, finding kinematic deviations in the low acceleration regime that challenge Newtonian dynamics.
• Results indicate non-Newtonian behavior for binaries with accelerations below twice the MOND threshold, consistent with Modified Newtonian Dynamics.
• The findings suggest a potential need to reconsider gravitational theories in low acceleration environments, offering support for MOND-like models over traditional dark matter explanations for these anomalies.

Anomalous Internal Kinematics in Wide Binaries from Gaia DR3

The study presented examines the internal kinematics of wide binary systems using data from the Gaia DR3 catalogue, focusing specifically on the anomalies observed in the low acceleration regime. This research explores the gravitational phenomena traditionally attributed to dark matter by investigating wide binaries, systems that experience similar acceleration conditions found in the outer regions of spiral galaxies.

Key Findings

The primary analysis conducted confirms a non-Newtonian behavior in the kinematics of wide binaries, particularly when they are subjected to accelerations less than twice the MOND (Modified Newtonian Dynamics) threshold of $a_0 \approx 1.2 \times 10^{-10} \text{m s}^{-2}$. Some salient points from the paper include:

• Wide Binary Analysis: Using the enhanced Gaia DR3 data, which includes a more extensive set of radial velocities and internal stellar mass determinations, the study achieves a more precise analysis than previous attempts. This meticulous approach provides a clearer observation of anomalies in low acceleration regimes while filtering out potential noise and contaminants such as undetected stellar components or spurious projections.
• Results of the Low Acceleration Regime: The study finds that for binaries with separations greater than 0.01 parsecs, the relative velocities deviate from classical Newtonian predictions and indicate a modified gravitational model. These results are consistent with the MOND hypothesis, suggesting an effective deviation from Newtonian dynamics in regions characterized by accelerations $a < 2a_0$.
• Mass-velocity Scaling: The analysis reveals that at large separations, velocity dispersion among binary systems settles at a constant value rather than following Newtonian expectations, which would predict a continuous decline. This constant velocity aligns with the extra forces proposed by MOND-type dynamics.
• Kinematic Contaminants: The paper discusses the possibility of kinematic contaminants, such as hidden tertiary components or unbound stellar encounters, which could potentially mimic the observed anomalies. However, comprehensive data filtering techniques employed in the study minimize such contaminants, rendering the non-Newtonian results significant.

Implications and Future Directions

The results presented have substantial implications in both theoretical and practical domains:

1. Theory of Gravity: This study suggests the potential necessity of reconsidering gravity theories, especially in low acceleration environments. While dark matter has traditionally been invoked to account for such anomalies in galactic dynamics, the evidence here supports MOND-like models, proposing a modification to gravitational laws themselves under specific conditions.
2. Galactic Dynamics and Cosmology: By confirming the anomalies akin to those observed at galactic scales within much smaller and less massive systems, the research potentially narrows the interpretation of dark matter effects and theories tailoring galactic and cosmic structure dynamics.
3. Further Investigations: Future research could expand upon these findings by leveraging the forthcoming Gaia data releases, expected to encompass longer time baselines and refined measurements. This would allow a more in-depth exploration of the internal kinematics of even broader samples of wide binaries, enhancing the precision of gravitational anomaly assessments.

In conclusion, Hernandez's work with Gaia DR3 data provides strong empirical evidence for peculiar kinematics in wide binaries that challenge Newtonian gravitational dynamics in the low acceleration regime, emphasizing the need for further exploration into modified gravity theories.