Constraints on the Size of Extra Dimensions from the Orbital Evolution of Black-Hole X-Ray Binaries

TL;DR

This paper uses observations of black-hole X-ray binaries to place constraints on the size of extra dimensions predicted by braneworld gravity models, finding that current data limits are comparable to laboratory experiments.

Contribution

It provides observational constraints on extra-dimensional models by analyzing orbital period changes in black-hole X-ray binaries, linking astrophysical data with fundamental physics.

Findings

Upper limit on the orbital period change of A0620-00

Constraints on the curvature radius of extra dimensions

Any observed period increase indicates physics beyond general relativity

Abstract

One of the plausible unification schemes in physics considers the observable universe to be a 4-dimensional surface (the "brane") embedded in a higher-dimensional curved spacetime (the "bulk"). In such braneworld gravity models with infinitely large extra dimensions, black holes evaporate fast through the emission of the additional gravitational degrees of freedom, resulting in lifetimes of stellar-mass black holes that are significantly smaller than the Hubble time. We show that the predicted evaporation rate leads to a change in the orbital period of X-ray binaries harboring black holes that is observable with current instruments. We obtain an upper limit on the rate of change of the orbital period of the binary A0620-00 and use it to constrain the asymptotic curvature radius of the extra dimension to a value comparable to the one obtained by table-top experiments. Furthermore we argue that any measurement of a period increase for low-mass X-ray binaries with a high mass ratio is evidence for new physics beyond general relativity and the standard model.