Our simulations, despite probing quite different jet velocities and resolution levels, point to a very unstable nature of the structure resulting from the jet–wind–orbit interaction in HMMQ. Although this was already suggested, our numerical calculations strongly endorse this possibility. Our results, not being an extensive exploration but just two characteristic examples, do not settle the issue for other parameter choices. Nevertheless, the simulations probe fiducial cases and their outcomes suggest that the jet is unlikely to leave unscathed the region close to the binary, say $z\lesssim 10\, a$. Even for smaller χj values and longer Porb values than those explored here, we propose that jet–wind–orbit interaction could induce instability growth, which could produce precession–like patterns in the jets at larger scale. Even if the jets are so powerful that significant mixing and disruption does not occur on scales $\sim 1-10\, a$, and Φ is initially rather small, the growth of Kelvin–Helmholtz (KH) instabilities is expected (see also, e.g. Perucho 2019, in the context of extragalactic jets). In fact, the jet–wind interaction alone can already perturb the jet (Perucho & Bosch-Ramon 2008; Perucho et al. 2010), and stellar wind clumping, not considered in the present simulations, should also render the jet more prone to disruption (Perucho & Bosch-Ramon 2012). In addition to KH instabilities, Rayleigh–Taylor and Richtmyer–Meshkov instabilities could also develop at the dynamical jet–wind contact discontinuity, particularly due to the Coriolis force, as in the similar case studied by Bosch-Ramon et al. (2015) with a pulsar wind instead of a jet. These additional instabilities would produce non-linear perturbations that would couple to the KH instability, enhancing the disruptive effects of all these processes.5 We note that jet precession-like features caused by KH instabilities may or may not follow the orbital period, as these instabilities could span a broad range of wavelengths. Therefore, in addition to the cases explored here, χj values even smaller than θj (see Bosch-Ramon & Barkov 2016, for a discussion on the χj – θj relation) could also lead to distorted jets on scales ≫a. Interestingly, this has been observed in radio in Cyg X-3, but not yet in Cyg X-1 (see,e.g. Mioduszewski et al. 2001; Miller-Jones et al. 2004; Tudose et al. 2007, for related radio observations of Cyg X-3). Interestingly, regardless of the χj value, if the jet gets disrupted on scales $\lesssim 10\, a$, the strong pressure drop outwards of the embedding medium can make the jet–wind mixed flow turn into a collimated structure (see Bosch-Ramon & Barkov 2016; see also Millas et al. 2019 for the case of the HMMQ SS 433, a different but related situation -see Section 1-). In the case of a weaker wind-orbit effect on the jet, the jet inertia, and the density drop of the medium, may allow the jet to keep some coherence despite KH instability growth, at least until interacting with the surrounding medium on much larger scales (see, e.g. Marti et al. 1996; Gallo et al. 2005; Russell et al. 2007; Sell et al. 2015 for Cyg X-1 radio observations, and Bordas et al. 2009; Bosch-Ramon et al. 2011; Yoon et al. 2011 for simulations, of the jet-medium interaction). To properly study the evolution of orbit-affected jets at z ≫ a in HMMQ, devoted simulations are planned.
Citation: Perucho et al. 2010
Citation function: Background