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Theses

Simulation of relativistic jets in high-mass microquasars

Abstract : Microquasars, high-energy sources made of an accreting black hole and a stellar companion, are complex astrophysical objects where various physical phenomenon are at play. The name microquasar originates in the similarities found with quasars, an outdated term for a subcase of active galactic nuclei, especially the presence of a relativistic jet visible in radio. The energy loss related to these radiations, as well as other plasma processes, is not taken into account while simulating relativistic jets. Moreover, studies of microquasar jets are either performed with relativistic flow over small scales (sim one orbital separation) or Newtonian flow over large scales (tens of orbital separations), but not relativistic over large scales. This PhD thesis thus aim at filling the gap from both of these considerations.Firstly, I developed analytical formulas for the cooling of an astrophysical plasma, as well as numerical tools aiming to precisely analyse and quantify simulated relativistic hydrodynamical jets. These tools were then used to study the impact of including the aforementioned cooling in state-of-the-art numerical simulations of hydrodynamical, relativistic jets over a large spatial and temporal scale. This study was performed with numerical setups based on the microquasars Cygnus X-1 and Cygnus X-3, which were (tentatively) reproduced for this PhD.This PhD found that adding radiative losses induced a differential cooling between the jet beam and the surrounding cocoon. This differential cooling strengthens the overpressure of the latter over the former, which in turn modifies the jet internal structure, accelerating the growth of the Kelvin-Helmholtz instability, destabilising the jet and thus impacting its global structure and dynamics.A parametric study around the chosen parameters for Cygnus X-1 and Cygnus X-3 was also performed. Results from previous studies such as jet bending and jet disruption by the stellar wind are confirmed, and the impact of the jet temperature on its stability and dynamics was investigated. A threshold effect is found: when the injected temperature is greater than the temperature to which the first recollimation shock would heat injected material of this density and velocity, the instability growth results in sensibly different dynamical properties of the jet.
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Submitted on : Friday, March 25, 2022 - 2:14:07 PM
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Long-term archiving on: : Sunday, June 26, 2022 - 6:59:06 PM

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  • HAL Id : tel-03619941, version 1

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Arthur Charlet. Simulation of relativistic jets in high-mass microquasars. Solar and Stellar Astrophysics [astro-ph.SR]. Université Montpellier, 2021. English. ⟨NNT : 2021MONTS106⟩. ⟨tel-03619941⟩

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