Can Superconducting Cosmic Strings Piercing Seed Black Holes Generate Supermassive Black Holes in the Early Universe?

TL;DR

This paper proposes a novel mechanism where superconducting cosmic strings piercing seed black holes transfer energy, enabling rapid growth into supermassive black holes in the early universe, addressing the challenge of their rapid formation.

Contribution

It introduces a new scenario where cosmic strings with currents can significantly accelerate seed black hole growth, providing a potential solution to early SMBH formation.

Findings

Superconducting cosmic strings can transfer energy to seed black holes.

Estimated currents are sufficient to produce SMBHs by redshift 7.

Both topological and fundamental strings can generate early SMBHs.

Abstract

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.