A fundamental plane of black hole activity

• The scale invariance ansatz for the disc-jet coupling captures the main physical properties of these systems

• The correlation coefficient of the fundamental plane can be used to test accretion disc physics

• X-ray emission from BH accreting at less than a few % of the Eddington rate:

  • is unlikely to be produced by radiatively efficient accretion
  • is entirely consistent with (very general) models of radiatively inefficient accretion