Shrinking the Braneworld: Black Hole in a Globular Cluster
  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.
