  The Search for Extra-Terrestrial Intelligence (SETI) has so far been
unsuccessful and needs additional methods. We introduce a two-dimensional
metric for civilization development, using the Kardashev scale of energy
increase and the Barrow scale of inward manipulation. To support Barrow's scale
limit, we contend with energetic, societal, scientific, computational, and
philosophical arguments that black holes are attractors for intelligence. An
application of the two-dimensional metric leads to a simple, consistent and
observable hypothesis to test the existence of very advanced civilizations. We
suggest that some already observed X-Ray binaries may be unnoticed advanced
civilizations, of type KII-Bomega. The appendix provides an argumentative map
of the paper's main thesis.
  KEYWORDS: SETI, black holes, Kardashev scale, Barrow scale, star lifting, XRB
