The existence of medium-sized black holes has long been debated. Such an object has now been discovered in the centre of a dense cluster of stars, potentially enhancing our understanding of all black holes. See Letter p.203 Observational campaigns over several decades have targeted globular clusters for the signatures of intermediate-mass black holes—those with masses 100 to 10,000 times that of the Sun. But all of the candidates found in these searches are radio dim and lack the predicted X-ray to radio flux ratio. Here Bulent Kiziltan et al. report dynamical evidence, using timing data for millisecond pulsars, for a central black hole in the globular cluster 47 Tucanae with a mass of about 2,200 solar masses. The existence of such a black hole with no detectable electromagnetic counterpart, in the centre of such a dense cluster, suggests that it is not accreting quickly enough to produce a signal.