Broad K$\alpha$ iron line from accretion disks around traversable wormholes

Abstract

It has been proposed that the supermassive black hole candidates at the centers of galaxies might be wormholes formed in the early Universe and connecting our Universe with other sister Universes. The analysis of the profile of the relativistic K$\alpha$ iron line is currently the only available approach to probe the spacetime geometry around these objects. In this paper, I compute the expected K$\alpha$ iron line in some wormhole spacetimes and I compare the results with the line produced around Kerr black holes. The line produced in accretion disks around non-rotating or very slow-rotating wormholes is relatively similar to the one expected around Kerr black holes with mid or high value of spin parameter and current observations are still marginally compatible with the possibility that the supermassive black hole candidates in galactic nuclei are these objects. For wormholes with spin parameter $a_* \gtrsim 0.02$, the associated K$\alpha$ iron line is instead quite different from the one produced around Kerr black holes, and their existence may already be excluded.