We demonstrate that cosmic string loops may provide a joint resolution of two mysteries surrounding recently observed black holes. For a string tension in an appropriate range, large radius string loops have the potential to provide the nonlinearities in the early universe that seed supermassive black holes. The more numerous smaller radius string loops can then seed intermediate mass black holes, including those with a mass in the region between $65M_{\odot }$ and $135M_{\odot }$ in which standard black hole formation scenarios predict no black holes are able to form, but which have recently been detected by the LIGO/VIRGO Collaboration. We find that there could be as many as ${10}^6$ of intermediate mass black holes per galaxy, providing a tantalizing target for gravitational wave observatories to look for.

• Received 27 April 2021
• Accepted 12 November 2021

DOI:https://doi.org/10.1103/PhysRevD.104.123501