Wide binary stars have been intensely discussed as potential tools for exploring the nature of gravity under very low accelerations, weaker than about 1 nanometer per second squared. Understanding gravity in this weak acceleration regime is crucial because it is linked to concepts such as dark matter, the gravitational behaviors of astronomical systems, and fundamental principles of physics and cosmology.
If deviations from expected Newtonian behavior occur at these low accelerations, it could necessitate modifications or extensions to Einstein's general relativity, which has been highly successful except in low acceleration contexts.
Two independent studies, led by Kyu-Hyun Chae and Xavier Hernandez, suggest that data from wide binary stars in the European Space Agency's latest Gaia database shows deviations from Newtonian predictions, supporting modified gravity theories like modified Newtonian dynamics (MOND). This framework, introduced 40 years ago by Mordehai Milgrom, might explain these deviations.
Such a departure from Newtonian gravity at low accelerations could signify a scientific paradigm shift with profound implications. To address these important issues and in response to conflicting claims, Chae conducted a new analysis. He examined a comprehensive range of samples, included various hierarchical systems, and utilized all methods previously published, aiming to clarify the challenges to his earlier findings of a gravitational anomaly.
Published in The Astrophysical Journal on September 9, 2024, Chae's study concluded that all methods and samples used consistently supported the existence of the gravitational anomaly he first identified. According to Chae, this anomaly, which suggests a roughly 40% increase in gravitational pull when accelerations drop below about 0.1 nanometers per second squared, aligns with MOND predictions.
MOND, like Newtonian and Einsteinian gravity, adheres to the universality of free fall, but it differs by not assuming the strong equivalence principle. This allows for variations in internal dynamics under a static external field. In contrast to Newton's and Einstein's theories, which expect wide binaries falling through the Milky Way's field to follow Kepler's laws, MOND predicts deviations influenced by the Milky Way's external field, approximately 0.2 nanometers per second squared, about 40% different from traditional predictions.
Despite these intriguing results, further reproductions and confirmations are necessary for the gravitational anomaly to be widely accepted as scientific fact. The anomaly needs continual examination to impose constraints on theoretical models.
Researchers are keenly watching for new data and improved methodologies to better understand this anomaly, especially through precise measurements of the stars' line-of-sight velocities, which could provide more comprehensive insight into these gravitational phenomena.
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