Study of large binary stars reveals new evidence of altered gravity at low acceleration

A new study published in The Astrophysics Journal reveals new evidence that standard gravity decays in an idiosyncratic manner at low acceleration. This new study strengthens evidence for altered gravity that was previously reported in 2023 from an analysis of the orbital motions of gravitationally related, widely separated (or long-period) binary stars, known as wide binaries .

The new study was carried out by Kyu-Hyun Chae, a professor of physics and astronomy at Sejong University in Seoul, South Korea, with large binaries observed by the European Space Agency’s Gaia space telescope.

The gravitational anomalies reported in 2023 by Chae’s study of wide binaries have the unique feature that orbital motions in binaries experience larger accelerations than Newtonian predictions when the mutual gravitational acceleration is less than about 1 nanometer per second squared and the acceleration factor becomes approximately 1.4 at accelerations. less than about 0.1 nanometer per square second.

This high acceleration in wide binaries cannot be explained by invoking undetected dark matter, because the required dark matter density is out of the question based on galactic dynamics and cosmological observations.

Remarkably, the high acceleration agrees well with what MOND-type theories of modified gravity (modified Newtonian dynamics) such as AQUAL predict under the external field effect of the Milky Way. The MOND paradigm was suggested by physicist Mordehai Milgrom and the AQUAL theory was formulated by him and the late physicist Jacob Bekenstein 40 years ago.

Since gravitationally bound astrophysical systems, such as galaxies and galaxy clusters, as well as the universe itself, are governed by gravity, the breakdown of standard gravity at low acceleration has profound implications for astrophysics and cosmology. Thus, the importance of confirming or replicating the reported anomaly from as many independent studies as possible cannot be overemphasized. This led Chae to an independent study of wide binaries, although still based on the same Gaia database.

Chae’s new study focused on a clean sample of “pure” wide binaries by removing any systems that potentially host additional unobserved stars. The motivation was to avoid the burden (and associated potential errors) of calculating additional hidden gravitational effects and to compare the pure sample results with previous results.

Chae conservatively selected up to 2,463 pure binaries, less than 10% of the sample used in the previous study. Since the expected fraction of pure binaries among apparently binary systems is at least 50%, this much lower fraction means that the selection was sufficiently stringent.

Chae applied two algorithms to test gravity using a sample of pure binaries. In an algorithm initially developed from previous work on general or “impure” samples, he used a Monte Carlo method to calculate (the probability distribution of) the observed kinematic acceleration, defined by the velocity relative to the square of physical separation in real space. three-dimensional space, based on the Newtonian gravitational acceleration between the two stars, and then compared it to the corresponding Newtonian prediction of the kinematic acceleration.

In the other algorithm, simpler and suitable for pure binaries, Chae compared the observed distribution of relative velocities projected in the sky between the two stars relative to the separations projected in the sky with the distribution predicted by Newton via a Monte method Squidward.

Both algorithms produce consistent results that agree well with the previously reported gravitational anomaly. The acceleration or relative speed observed between the two stars naturally satisfies standard Newton-Einstein gravity at a sufficiently small separation or at a sufficiently large acceleration.

However, the observed relative acceleration or velocity begins to deviate from the Newtonian prediction at a separation of about 2,000 AU (astronomical units) and an acceleration of about 1 nanometer per second squared. Then there is an almost constant increase of about 40-50% in acceleration or a 20% increase in relative velocity at separation greater than about 5,000 au or acceleration less than about 0.1 nanometer per second squared, up to the probed limit of about 20,000 au. or 0.01 nanometers per square second.

Chae’s new results agree well with an independent result from Xavier Hernández’s group which, coincidentally, is currently in production. This is significant because Hernandez’s group selected their sample completely independently of Chae’s selection and used an independent algorithm (different from Chae’s two algorithms) based on the full distribution of relative velocities for their wide, pure binary pairs. .

Regarding the significance of the results, Chae says: “When I obtained direct evidence of the low-acceleration gravitational anomaly in 2023, I felt like I was dreaming. Since I have independent evidence from a ten times smaller sample of pure binaries thanks to “

Chae also points out that this new sample is explicitly free of any concerns about reduced data quality that have been raised in the literature thus far. Chae further clarifies the recent contradictory claim by Indranil Banik and his co-authors, stating: “There are many problems with their methodology and results. Their conclusion is invalid for two main reasons, among others.”

“In their sample selection, they consciously excluded binaries from the Newtonian regime that are crucial for accurately calibrating the rate of occurrence of systems containing additional hidden components. Then, they used a specific statistical algorithm for modeling the rates to infer severity, occurrence rate, and other parameters simultaneously, but ignored velocity errors although vital to their algorithm.

Chae concludes: “At least three independent quantitative analyzes by two independent groups reveal essentially the same gravitational anomaly. The gravitational anomaly is real and a new scientific paradigm shift is underway.”

The observed gravitational anomaly is remarkably consistent with MOND-type (Milgromian) gravitational phenomenology. However, underlying theoretical possibilities encompassing MOND-like gravitational phenomenology are currently open, which could be good news for theoretical physicists and mathematicians.

The large binary gravitational anomaly is reminiscent of Mercury’s perihelion precession anomaly first observed in the 19th century. The latter led to Einstein’s relativistic theory of gravity. What fundamental theory will the first lead to?