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Relativistic jets are launched from black hole (BH) X-ray binaries and activegalactic nuclei when the disk accretion rate is below a certain limit (i.e.,when the ratio of the accretion rate to the Eddingtion accretion rate,$\dot{m}$, is below about 0.01) but quenched when above. We propose a newparadigm to explain this observed coupling between the jet and the accretiondisk by investigating the extraction of the rotational energy of a BH when itis surrounded by different types of accretion disk. At low accretion rates(e.g., when $\dot{m}\lesssim0.1$), the accretion near the event horizon isquasi-spherical. The accreting plasmas fall onto the event horizon in a widerange of latitudes, breaking down the force-free approximation near thehorizon. To incorporate the plasma inertia effect, we consider themagnetohydrodynamical (MHD) extraction of the rotational energy from BHs by theaccreting MHD fluid, as described by the MHD Penrose process. It is found thatthe energy extraction operates, and hence a relativistic jet is launched,preferentially when the accretion disk consists of an outer Shakura-Sunyaevdisk (SSD) and an inner advection-dominated accretion flow. When the entireaccretion disk type changes into an SSD, the jet is quenched because theplasmas brings more rest-mass energy than what is extracted from the holeelectromagnetically to stop the extraction. Several other observed BH disk-jetcouplings, such as why the radio luminosity increases with increasing X-rayluminosity until the radio emission drops, are also explained.

Launching and Quenching of Black Hole Relativistic Jets at Low Accretion Rate