Shrinking the Braneworld: Black Hole in a Globular Cluster

TL;DR

This paper uses the black hole in a globular cluster to set the strongest astrophysical constraint on the size of extra dimensions in the RS2 braneworld model, limiting it to less than 0.003 mm.

Contribution

It demonstrates that the observed black hole's properties impose a new, tighter upper bound on the size of extra dimensions predicted by braneworld theories.

Findings

Maximum size of extra dimensions constrained to < 0.003 mm

Black hole's age and mass provide strong astrophysical limits

Limits are close to the absolute astrophysical bounds

Abstract

Large extra dimensions have been proposed as a possible solution to the hierarchy problem in physics. One of the suggested models, the RS2 braneworld model, makes a prediction that black holes evaporate by Hawking radiation on a short timescale that depends on the black hole mass and on the asymptotic radius of curvature of the extra dimensions. Thus the size of the extra dimensions can be constrained by astrophysical observations. Here we point out that the black hole, recently discovered in a globular cluster in galaxy NGC 4472, places the strongest constraint on the maximum size of the extra dimensions, L < 0.003 mm. This black hole has the virtues of old age and relatively small mass. The derived upper limit is within an order of magnitude of the absolute limit afforded by astrophysical observations of black holes.