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The Scientific World Journal
Volume 2013 (2013), Article ID 204315, 4 pages
Research Article

A Note on the Observational Evidence for the Existence of Event Horizons in Astrophysical Black Hole Candidates

1Arnold Sommerfeld Center for Theoretical Physics, Ludwig Maximilians University Munich, 80333 Munich, Germany
2Department of Physics, Fudan University, Shanghai 200433, China

Received 18 April 2013; Accepted 30 May 2013

Academic Editors: V. Beckmann, S. Covino, and V. Van Elewyck

Copyright © 2013 Cosimo Bambi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Black holes have the peculiar and intriguing property of having an event horizon, a one-way membrane causally separating their internal region from the rest of the Universe. Today, astrophysical observations provide some evidence for the existence of event horizons in astrophysical black hole candidates. In this short paper, I compare the constraint we can infer from the nonobservation of electromagnetic radiation from the putative surface of these objects with the bound coming from the ergoregion instability, pointing out the respective assumptions and limitations.