Orateur
Description
Relativistic jets are observed in some accreting black-hole systems but not others. In X-ray binaries, jet production is closely associated with geometrically thicker accretion states, suggesting that disk thickness may play a fundamental role in determining whether a black hole can launch a powerful jet. We investigate this connection using global three-dimensional GRMHD simulations of accretion disks with $h/r=0.1$–$0.3$, initialized with the same toroidal magnetization and with no large-scale poloidal, jet-launching magnetic flux initially threading the black hole.
We find that large-scale poloidal magnetic fields are generated self-consistently by the MRI dynamo, through the interaction of non-axisymmetric structures and differential rotation. The strength of this dynamo decreases sharply as the disk becomes thinner.
This weaker field generation also reduces MRI-driven angular-momentum transport and slows the inward transport of magnetic flux. Together, these effects produce a strong dependence of the magnetic flux accumulated by the black hole on disk thickness.
We predict a steep increase in the timescale required to accumulate jet-launching magnetic flux as the disk becomes thinner, with a difference of roughly four orders of magnitude between our thickest and thinnest disk cases. These results provide a physical connection between accretion-disk geometry, magnetic-field generation and transport, and the appearance and disappearance of relativistic jets.