Gravitational search for near Earth black holes or other compact dark
  objects
  Primordial black holes, with masses comparable to asteroids, are an
attractive possibility for dark matter. In addition, other forms of dark matter
could form compact dark objects (CDO). We search for small tidal accelerations
from low mass black holes or CDOs orbiting near the Earth, and find none. Using
about 10 years of data from the superconducting gravimeters in the Black Forest
Observatory in South-Western Germany and at Djougou, Northern Benin in Western
Africa we set an upper limit on the maximum mass of any dark object orbiting
the Earth as a function of orbital radius. For semi-major axis less than two
earth radii we exclude all black holes or CDOs with masses larger than
6.7x10^{13} kg. Lower mass primordial black holes may be strongly constrained
by Hawking radiation. We conclude that near Earth black holes are extremely
unlikely.
