Multipole Ratios : A New Window into Black Holes

*CC BY 3.0 (as fig. 1 from Event Horizon TelescopeCollaboration, K. Akiyama et al., First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring, Astrophys.J. Lett.875(2019), no. 1, L5,1906.11242 *)

More than a century after their theoretical discovery, black holes still hold many mysteries. We have developed new methods to calculate an infinite number of hitherto unknown parameters of any arbitrary black hole, some of which we believe could be observed in current and future experiments.

Half of these multipoles are finite, and the other half vanish. Any ratio of two vanishing moments thus seems to be ill-defined. By embedding black holes in string theory, we develop a novel method to define and calculate such multipole moment ratios unambiguously for any black hole. In this way, we find an infinite number of previously unknown multipole ratios for any **Kerr black hole**.

Our method can also be used to calculate multipole ratios for supersymmetric black holes. There exist a large number of horizonless geometries that have the same charges as these supersymmetric black holes and only differ from them close to the horizon. We also develop an independent second method to calculate multipole ratios using these “microstate geometries,” and find striking similarities between the results of the two methods.

Contact: Iosif Bena

E. De-laborderie, 2020-11-27 15:16:00