Letter

Nature 445, 183-185 (11 January 2007) | doi:10.1038/nature05434; Received 18 September 2006; Accepted 7 November 2006; Published online 3 January 2007

A black hole in a globular cluster

Thomas J. Maccarone1, Arunav Kundu2, Stephen E. Zepf2 & Katherine L. Rhode3,4

  1. School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
  2. Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
  3. Department of Astronomy, Wesleyan University, Middletown, Connecticut 06459, USA
  4. Department of Astronomy, Yale University, New Haven, Connecticut 06520, USA

Correspondence to: Thomas J. Maccarone1 Correspondence and requests for materials should be addressed to T.J.M. (Email: tjm@phys.soton.ac.uk).

Globular star clusters contain thousands to millions of old stars packed within a region only tens of light years across. Their high stellar densities make it very probable that their member stars will interact or collide. There has accordingly been considerable debate about whether black holes should exist in these star clusters1, 2, 3. Some theoretical work suggests that dynamical processes in the densest inner regions of globular clusters may lead to the formation of black holes of approx1,000 solar masses3. Other numerical simulations instead predict that stellar interactions will eject most or all of the black holes that form in globular clusters1, 2. Here we report the X-ray signature of an accreting black hole in a globular cluster associated with the giant elliptical galaxy NGC 4472 (in the Virgo cluster). This object has an X-ray luminosity of about 4 times 1039 erg s-1, which rules out any object other than a black hole in such an old stellar population. The X-ray luminosity varies by a factor of seven in a few hours, which excludes the possibility that the object is several neutron stars superposed.

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