Cosmic strings and primordial black holes
  Cosmic strings and primordial black holes (PBHs) commonly and naturally form
in many scenarios describing the early universe. Here we show that if both
cosmic strings and PBHs are present, their interaction leads to a range of
interesting consequences. At the time of their formation, the PBHs get attached
to the strings and influence their evolution, leading to the formation of
black-hole-string networks and commonly to the suppression of loop production
in a range of redshifts. Subsequently, reconnections within the network give
rise to small nets made of several black holes and connecting strings. The
number of black holes in the network as well as the stability of the nets
depend on the topological properties of the strings. The nets oscillate and
shrink exponentially due to the emission of gravitational waves. This leads to
potentially observable string-driven mergers of PBHs. The strings can keep PBHs
from galactic halos, making the current bounds on PBHs not generally
applicable. Alternatively, heavy PBHs can drag low-tension strings into the
centers of galaxies. The superconducting strings can appear as radio filaments
pointing towards supermassive black holes.
