Thermal conduction effects on the accretion–ejection mechanism. Outflow process investigation

Abstract

Astrophysical jets emanating from different systems are one of the most spectacular and enigmatic phenomena pervading the Universe. These jets are typically bipolar and span hundreds of thousands of light years, some even longer than the diameter of our Milky Way. The study of the disc-jet systems is motivated by the observed correlation between ejection and accretion signatures and is still under debate. It was shown in our previous work the crucial role of thermal conduction in the dynamics of a thin viscous resistive accretion disc orbiting a central object and was provided an unprecedented wealth of discussion that has advanced our understanding of the inflow process. In this work, we expand our exploration by addressing the most outstanding basic questions concerning the launching, acceleration and collimation processes of the jet in presence of thermal conduction. We also tackle in depth-analysis the effects of this physical ingredient on the time evolution of temperature and on mass fluxes such as inflow and outflow rates. We performed a series of 2.5 D non-relativistic time-dependent numerical calculations of a disc-jet system using the PLUTO code. Our results revealed compelling evidence that thermal conduction contributes to launching a faster and more collimated jet. The mass extracted from the disc via the outflow channel is also affected by the presence of thermal conduction in the sense that the ejection efficiency is significantly improved.

Angular momentum and energy transport in disc–jet systems: Unravelling the contribution of saturated thermal conduction

“…The turbulent nature of the plasma plays a crucial role in determining these transport coefficients. It is important to highlight that the mean field approximation has been effectively employed in numerical investigations of the disc-jet system (Zanni et al 2007;Romanova et al 2009;Tzeferacos et al 2009;Murphy, Ferreira, & Zanni 2010;Rezgui et al 2019Rezgui et al , 2022, as well as in semi-analytical studies (Ogilvie & Livio 2001;Rothstein & Lovelace 2008).…”

“…Equation ( 16) derives the toroidal velocity from the radial equilibrium, whereas equation ( 17) derives the radial speed from the angular momentum conservation equation. The launch of a robust jet from the inner part of the disc takes place in a short timescale if we initially impose an accretion movement according to the relation described in equation ( 18) (Murphy, Ferreira, & Zanni 2010;Sheikhnezami et al 2012;Rezgui et al 2019Rezgui et al , 2022.…”

“…We apply boundary conditions identical to those previously used in (Rezgui et al 2019(Rezgui et al , 2022. This maintains axial symmetry on the rotation axis and equatorial symmetry for the disc midplane.…”

“…We follow the same strategy as previous studies in literature, where the sink is treated as an internal boundary condition (Murphy, Ferreira, & Zanni 2010;Tzeferacos et al 2009Tzeferacos et al , 2013. This latter has been discussed in our previous article Rezgui et al (2022) (see Section 2.3). The most important point to consider is that we impose the non-positivity of the poloidal velocity in this area to ensure that no artificial outflows are permitted to leave the sink.…”

“…All the above-mentioned investigations have neglected this physical ingredient, notwithstanding its importance. Our previous papers (Rezgui et al 2019(Rezgui et al , 2022 are considered, in terms of time-dependent simulations, to be the first initiatives in studying the contribution of thermal conduction in the evolution of the accretion-ejection structures with particular emphasis on a geometrically thin disc. In fact, by including three nonideal effects together, viscosity, resistivity, and thermal conduction, we demonstrated in Rezgui et al (2019) that thermal conduction plays a significant role in the dynamics of a viscous resistive accretion disc by presenting a thorough analysis of its impacts on the evolution of fundamental aspects of the inflow properties with a focus on the equatorial plane and disc surface.…”