Speaker: Hung-Yi Pu (National Tsing Hua University, Taiwan)

Abstract: Relativistic jets can be launched form the black hole (BH) ergosphere by extracting the rotational energy of the black hole. When the BH magnetosphere is nearly vacuum, the extraction can be realized by the help of large-scale, hole-threading magnetic fields, as described by the Blandford-Znajek process. For accreting BH systems,  on the other hand, the plasma near the horizon can further modify the Blandford-Znajek process by loading onto the field lines. Such modification is important when accretion flow near the event horizon has a quasi-spherical geometry. By investigating the extraction of the rotational energy from BH at different accretion rate (and therefore accretion disk type), we conclude that the relativistic jets can  preferentially take place when the BH is surrounded by a combined disk (which consists of an outer thin disk and inner advection-dominated accretion flow) and a slim disk, but become less active or being quenched when surrounded by an advection-dominated accretion flow or a thin disk. Puzzling observed disk-jet features of black hole binaries and AGNs, such as why their radio emission suddenly drops when the dimensionless accretion rate , the ratio between the accretion rate and the Eddington accretion rate, exceeds a certain limit (~0.01), are also explained.