--------------------------------------------------------------------------------------------------------
Title: Gaia measurements of the low-acceleration gravitational anomaly in wide binary stars

Speaker: Prof. Kyu-Hyun Chae (Sejong University)

Date&Time: 2024-03-22, 11:00 AM

Location: Science Hall B101

Talk to be delivered in Korean
--------------------------------------------------------------------------------------------------------

Abstract: European Space Agency’s Gaia satellite provides state-of-the-art data of proper motions (transverse velocities), parallaxes (distances), radial velocities, and luminosities for nearby stars. Statistical analyses of binary stars show that the Newton-Einstein standard gravity holds accurately for the orbit size less than about 1000 astronomical units (au) or the internal acceleration greater than about 6 nanometer per second squared. However, binary orbital motions exhibit a gradual systematic anomaly from 1000 to 5000 au and a pseudo-Newtonian gravity with Newton’s constant boosted by a factor of 1.3 – 1.5 holds for > 5000 au. Remarkably, this behavior agrees with the prediction of Milgromian (modified Newtonian dynamics) gravity. Consistent results are obtained from three independent methods of statistical analysis, the ``acceleration plane analysis”, the “normalized velocity profile analysis”, and the “stacked velocity profile analysis” based on various samples of binaries. These results robustly show that general relativity breaks down in the low acceleration limit. Thus, despite all the experimental successes of general relativity outside the low-acceleration regime, the low-acceleration gravitational anomaly reveals its boundaries. Implications of the results for cosmology and theoretical physics and future prospect are discussed.