Connecting the Extremes: A Story of Supermassive Black Holes and
  Ultralight Dark Matter
  The formation of ultra rare supermassive black holes (SMBHs), with masses of
$\mathcal O(10^9\,M_\odot)$, in the first billion years of the Universe remains
an open question in astrophysics. At the same time, ultralight dark matter (DM)
with mass in the vicinity of $\mathcal O(10^{-20}~\text{eV})$ has been
motivated by small scale DM distributions. Though this type of DM is
constrained by various astrophysical considerations, certain observations could
be pointing to modest evidence for it. We present a model with a confining
first order phase transition at $\sim 10$ keV temperatures, facilitating
production of $\mathcal O(10^9\,M_\odot)$ primordial SMBHs. Such a phase
transition can also naturally lead to the implied mass for a motivated
ultralight axion DM candidate, suggesting that SMBHs and ultralight DM may be
two sides of the same cosmic coin. We consider constraints and avenues to
discovery from superradiance and a modification to $N_{\rm eff}$. On general
grounds, we also expect primordial gravitational waves -- from the assumed
first order phase transition -- characterized by frequencies of $\mathcal
O(10^{-12}-10^{-9}~\text{Hz})$. This frequency regime is largely uncharted, but
could be accessible to pulsar timing arrays if the primordial gravitational
waves are at the higher end of this frequency range, as could be the case in
our assumed confining phase transition.
