  We study the phenomenology of string bosenova explosions in vector
superradiance clouds around spinning black holes, focusing on the observable
consequences in gravitational wave detectors and accelerometers. During the
growth of the superradiance cloud, the dark gauge field might reach a critical
field strength, when a network of dark photon strings is produced via a
superheated phase transition. These dark photon strings will then absorb the
energy in the background fields and get ejected from the cloud, with total
energy as large as the rotational energy of the black hole. In this paper, we
study the subsequent evolution of this dense string network, and the resulting
observational consequences depending on the unknown string tension, or almost
equivalently, the ratio between the quartic and the gauge coupling in the
Abelian Higgs model. Strings with large tension will dissipate into
gravitational waves, detectable over a wide range of frequencies, from $\sim$
nHz near supermassive black holes, to $\gtrsim 10$ MHz around stellar mass
black holes. This is the first known source of high frequency gravitational
waves, unconstrained by cosmological observations. The strain of this
gravitational wave can be larger than $10^{-14}$ at low frequencies, lasting
for longer than typical duration of experiments. Small tension strings, with
total lengths in the network as large as $10^{40}$ km, can travel to the earth
with appreciable rate from any black hole in the Milky Way and interact with
earth based accelerometers. If the Standard Model particles are directly
charged under the dark photon, e.g. B-L, this interaction leads to an
acceleration of Standard Model particles that is independent of the coupling
constant. We work out the spectral density of this acceleration, and project
that modern accelerometers and equivalence principle tests can be sensitive to
the passing of these strings.
