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 .