Can Superconducting Cosmic Strings Piercing Seed Black Holes Generate
  Supermassive Black Holes in the Early Universe?
  The discovery of a large number of supermassive black holes (SMBH) at
redshifts $z > 6$, when the Universe was only 900 million years old, raises the
question of how such massive compact objects could form in a cosmologically
short time interval. Each of the standard scenarios proposed, involving rapid
accretion of seed black holes or black hole mergers, faces severe theoretical
difficulties in explaining the short-time formation of supermassive objects. In
this work we propose an alternative scenario for the formation of SMBH in the
early Universe, in which energy transfer from superconducting cosmic strings
piercing small seed black holes is the main physical process leading to rapid
mass increase. As a toy model, the accretion rate of a seed black hole pierced
by two antipodal strings carrying constant current is considered. Using an
effective action approach, which phenomenologically incorporates a large class
of superconducting string models, we estimate the minimum current required to
form SMBH with masses of order $M = 2 \times 10^{9}M_{\odot}$ by $z = 7.085$.
This corresponds to the mass of the central black hole powering the quasar ULAS
J112001.48+064124.3 and is taken as a test case scenario for early-epoch SMBH
formation. For GUT scale strings, the required fractional increase in the
string energy density, due to the presence of the current, is of order
$10^{-7}$, so that their existence remains consistent with current
observational bounds on the string tension. In addition, we consider an
"exotic" scenario, in which an SMBH is generated when a small seed black hole
is pierced by a higher-dimensional $F-$string, predicted by string theory. We
find that both topological defect strings and fundamental strings are able to
carry currents large enough to generate early-epoch SMBH via our proposed
mechanism.
