Looking for ultralight dark matter near supermassive black holes
  Measurements of the dynamical environment of supermassive black holes (SMBHs)
are becoming abundant and precise. We use such measurements to look for
ultralight dark matter (ULDM), which is predicted to form dense cores
("solitons") in the centre of galactic halos. We search for the gravitational
imprint of an ULDM soliton on stellar orbits near Sgr A* and by combining
stellar velocity measurements with Event Horizon Telescope imaging of M87*.
Finding no positive evidence, we set limits on the soliton mass for different
values of the ULDM particle mass $m$. The constraints we derive exclude the
solitons predicted by a naive extrapolation of the soliton-halo relation, found
in DM-only numerical simulations, for $2\times10^{-20}~{\rm eV}\lesssim
m\lesssim8\times10^{-19}~{\rm eV}$ (from Sgr A*) and
$m\lesssim4\times10^{-22}~{\rm eV}$ (from M87*). However, we present
theoretical arguments suggesting that an extrapolation of the soliton-halo
relation may not be adequate: in some regions of the parameter space, the
dynamical effect of the SMBH could cause this extrapolation to over-predict the
soliton mass by orders of magnitude.
