  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.

General Relativity and Quantum Cosmology;High Energy Astrophysical Phenomena