Smoking-gun evidence for modified gravity at low acceleration from Gaia observations of wide binary stars

A recent research reveals credible analysis of the orbital movements of long-period, widely spaced binary stars, commonly known as wide binaries in astronomy and astrophysics, that provides strong evidence for the breakdown of normal gravity at the low acceleration limit.

Up to 26,500 broad binaries within 650 light years (LY) were employed in the work by Kyu-Hyun Chae, professor of physics and astronomy at Sejong University in Seoul, who used data from the Gaia satellite observatory. The Astrophysical Journal's edition for August 1, 2023, has the study's publication.

Chae's study concentrated on computing the gravitational accelerations experienced by binary stars as a function of their spacing, or alternatively the orbital period, through a Monte Carlo deprojection of observed sky-projected movements to the three-dimensional space. This was a significant advancement over previous research.

Considering that the gravitational field itself is an acceleration, Chae argues, "From the beginning it seemed evident to me that gravity could be evaluated most directly and effectively by computing accelerations. I came up with this concept after my recent study with galactic rotation curves. Galactic disks and wide binaries have certain similarities in their orbits, however hydrogen gas particles in a galactic disk have approximately circular orbits whereas wide binaries have very elongated orbits.

Chae also measured the frequency of concealed nested inner binaries at a benchmark acceleration, which is different from prior research.

According to the study, general relativity and Newton's universal law of gravity both predict that an orbit between two stars will vary from one another when the accelerations are less than one millimeter per second squared.

The measured acceleration is around 30 to 40% greater than the Newton-Einstein prediction for accelerations less than 0.1 nanometer per second squared. The significance is quite high and satisfies the traditional standard for a scientific discovery, 5 sigma. Two separate acceleration bins in a sample of 20,000 broad binaries with a distance limit of 650 LY each exhibit variances with > 5 sigma significance in the same direction.

The reported rise of accelerations at lower accelerations is a puzzle because the measured accelerations higher than around 10 nanometer per second squared correspond well with the Newton-Einstein prediction from the same research. Intriguingly, this breakdown of the Newton-Einstein theory at accelerations weaker than approximately one nanometer per second squared was proposed 40 years ago by theoretical physicist Mordehai Milgrom at the Weizmann Institute in Israel in a new theoretical framework known as modified Newtonian dynamics (MOND) or Milgromian dynamics in current usage.

Additionally, the Milgrom and the late physicist Jacob Bekenstein's AQUAL MOND-type Lagrangian theory of gravity accurately predicts the boost factor of roughly 1.4. It is interesting that the right boost factor necessitates the Milky Way galaxy's external field effect, which is a singular prediction of MOND-type modified gravity. As a result, the vast binary data reveal both the breakdown of Newtonian dynamics and the appearance of modified gravity's external field impact.

In response to the findings, Chae asserts that "it appears improbable that a conspiracy or unidentified systematic might induce this acceleration-dependent breakdown of the standard gravity in conformity with AQUAL. I have investigated every potential systematic as outlined in the lengthy text. The outcomes are accurate. I predict that future research will use better and more comprehensive data to validate and improve the findings. For the sake of transparency and to assist any interested scholars, I have also made all of my codes available.

Wide binary dynamics cannot be influenced by dark matter, even if it existed, unlike galaxy rotation curves where the observed enhanced accelerations may, in theory, be attributed to it under the Newton-Einstein standard gravity. According to the MOND framework, the weak acceleration limit is where the conventional gravity just fails.

Wide binary dynamics has important ramifications for cosmology, theoretical physics, and astrophysics. Einstein's general relativity was finally inspired by anomalies in Mercury's orbits that were discovered in the nineteenth century.

A new theory that extends general relativity to the low acceleration MOND limit is now necessary to explain abnormalities in broad binaries. Despite all of Newton's gravity's triumphs, general relativity is required to explain relativistic gravitational phenomena like gravitational waves and black holes. Similarly, despite all of general relativity's achievements, a new theory is required to explain MOND events in the weak acceleration limit. The ultraviolet disaster of classical electrodynamics, which gave rise to quantum physics, may share some similarities with the weak-acceleration catastrophe of gravity.

Wide binary anomalies are a catastrophe for conventional gravity and cosmology, which rely on the ideas of dark matter and dark energy. There is no longer a requirement for a significant amount of dark matter in galaxies or even the cosmos because gravity follows MOND. Chae, who, like most scientists, "believed in" dark matter up until a few years ago, is likewise quite surprised by this.

A new physics revolution appears to be underway right now. According to Milgrom, Chae's discovery is the product of an intricate study of cutting-edge data that, in my opinion, was carried out extremely painstakingly and thoroughly. However, we need independent investigations to corroborate such a broad finding—which is in fact quite broad—preferably with better future data.

"This anomaly will have enormous implications for astrophysics, cosmology, and for fundamental physics at large if it is confirmed as a breakdown of Newtonian dynamics, and especially if it indeed agrees with the most straightforward predictions of MOND."

It is exciting that the departure from Newtonian gravity that my group has claimed for some time has now been independently confirmed, and impressive that this departure has for the first time been correctly identified as accurately corresponding to a detailed MOND model, according to Xavier Hernandez, professor at UNAM in Mexico who first proposed wide binary tests of gravity ten years ago. The Gaia satellite's unparalleled precision, the sizeable and carefully chosen sample that Chae utilizes, and his thorough analysis make his findings sufficiently reliable to be considered a discovery.

Professor Pavel Kroupa, who teaches at both Charles University in Prague and the University of Bonn, has reached the same findings about the law of gravity. The findings now strongly suggest that gravity is Milgromian rather than Newtonian, he claims, citing both this test on broad binaries and our experiments on open star clusters close to the sun. There are significant ramifications for all of astrophysics.