Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOn the transfer of momentum from stellar jets to molecular outflows
207
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
While it is generally thought that molecular outflows from young stellar objects (YSOs) are accelerated by underlying stellar winds or highly collimated jets, the actual mechanism of acceleration remains uncertain. The most favoured model, at least for low and intermediate mass stars, is that the molecules are accelerated at jet-driven bow shocks. Here we investigate, through high resolution numerical simulations, the efficiency of this mechanism in accelerating ambient molecular gas without causing dissociation. The efficiency of the mechanism is found to be surprisingly low suggesting that more momentum may be present in the underlying jet than previously thought. We also compare the momentum transferring efficiencies of pulsed versus steady jets. We find that pulsed jets, and the corresponding steady jet with the same average velocity, transfer virtually the same momentum to the ambient gas. The additional momentum ejected sideways from the jet beam in the case of the pulsed jet only serves to accelerate post-shock jet gas which forms a, largely atomic, sheath around the jet beam. For both the steady and pulsing jets, we find a power law relationship between mass and velocity ($m(v) propto v^{-gamma}$) which is similar to what is observed. We also find that increasing the molecular fraction in the jet decreases $gamma$ as one might expect. We reproduce the so-called Hubble law for molecular outflows and show that it is almost certainly a local effect in the presence of a bow shock.
rate research
Read More
We review some aspects of the bipolar molecular outflow phenomenon. In particular, we compare the morphological properties, energetics and velocity structures of outflows from high and low-mass protostars and investigate to what extent a common source model can explain outflows from sources of very different luminosities. Many flow properties, in particular the CO spatial and velocity structure, are broadly similar across the entire luminosity range, although the evidence for jet-entrainment is still less clear cut in massive flows than in low-mass systems. We use the correlation of flow momentum deposition rate with source luminosity to estimate the ratio f of mass ejection to mass accretion rate. From this analysis, it appears that a common driving mechanism could operate across the entire luminosity range. However, we stress that for the high-mass YSOs, the detailed physics of this mechanism and how the ejected wind/jet entrains ambient material remain to be addressed. We also briefly consider the alternative possibility that high-mass outflows can be explained by the recently proposed circulation models, and discuss several shortcomings of those models. Finally, we survey the current evidence on the nature of the shocks driven by YSOs during their pre-main-sequence evolution.
UltraFast Outflows (UFOs), seen as X-ray blueshifted absorption lines in active galactic nuclei (AGNs), are considered to be a key mechanism for AGN feedback. In this scenario, UFO kinetic energy is transferred into the cold and extended molecular outflow observed at the mm/sub-mm wavelength, which blows away the gas and suppresses star formation and accretion onto the central black hole (BH). However, the energy transfer between the inner UFO and the outer molecular outflow has not yet fully studied mainly due to the limited sample. In this paper, we performed comparison of their kinetic energy using the mm/sub-mm published data and the X-ray archival data. Among fourteen Seyfert galaxies whose molecular outflows are detected in the IRAM/PdBI data, eight targets are bright enough to perform spectral fitting in X-ray, and we have detected UFO absorption lines in six targets with 90% significance level, using XMM-Newton and Suzaku satellites. The time-averaged UFO kinetic energy was derived from the spectral fitting. As a result, we have found that the energy-transfer rate (kinetic energy ratio of the molecular outflow to the UFO) ranges from $sim7times10^{-3}$ to $sim$1, and has a negative correlation with the BH mass, which shows that the AGN feedback is more efficient in the lower mass BHs. This tendency is consistent with the theoretical prediction that the cooling time scale of the outflowing gas becomes longer than the flow time scale when the BH mass is smaller.
In this review we focus on the role jets and outflows play in the star and planet formation process. Our essential question can be posed as follows: are jets/outflows merely an epiphenomenon associated with star formation or do they play an important role in mediating the physics of assembling stars both individually and globally? We address this question by reviewing the current state of observations and their key points of contact with theory. Our review of jet/outflow phenomena is organized into three length-scale domains: Source and Disk Scales ($0.1-10^2$ au) where the connection with protostellar and disk evolution theories is paramount; Envelope Scales ($10^2-10^5$ au) where the chemistry and propagation shed further light on the jet launching process, its variability and its impact on the infalling envelope; Parent Cloud Scales ($10^5-10^6$ au) where global momentum injection into cluster/cloud environments become relevant. Issues of feedback are of particular importance on the smallest scales where planet formation regions in a disk may be impacted by the presence of disk winds, irradiation by jet shocks or shielding by the winds. Feedback on envelope scales may determine the final stellar mass (core-to-star efficiency) and envelope dissipation. Feedback also plays an important role on the larger scales with outflows contributing to turbulent support within clusters including alteration of cluster star formation efficiencies (feedback on larger scales currently appears unlikely). A particularly novel dimension of our review is that we consider results on jet dynamics from the emerging field of High Energy Density Laboratory Astrophysics (HEDLA). HEDLA is now providing direct insights into the 3-D dynamics of fully magnetized, hypersonic, radiative outflows.
We aimed to map the jets and outflows from the Serpens South star forming region and find an empirical relationship between the magnetic field and outflow orientation. Near-infrared H2 v=1-0 S(1) 2.122{mu}m -line imaging of the sim 30-long filamentary shaped Serpens South star forming region was carried out. K s broadband imaging of the same region was used for continuum subraction. Candidate driving sources of the mapped jets/outflows are identified from the list of known protostars and young stars in this region, which was derived from studies using recent Spitzer and Herschel telescope observations. 14 Molecular Hydrogen emission-line objects(MHOs) are identified using our continuum-subtracted images. They are found to constitute ten individual flows. Out of these, nine flows are located in the lower-half(southern) part of the Serpens South filament, and one flow is located at the northern tip of the filament. Four flows are driven by well-identified Class 0 protostars, while the remaining six flows are driven by candidate protostars mostly in the Class I stage, based on the Spitzer and Herschel observations. The orientation of the outflows is systematically perpendicular to the direction of the near-infrared polarization vector, recently published in the literature. No significant correlation was observed between the orientation of the flows and the axis of the filamentary cloud.
In this book chapter, we will briefly review the current empirical understanding of the relation between accretion state and and outflows in accreting stellar mass black holes. The focus will be on the empirical connections between X-ray states and relativistic (`radio) jets, although we are now also able to draw accretion disc winds into the picture in a systematic way. We will furthermore consider the latest attempts to measure/order jet power, and to compare it to other (potentially) measurable quantities, most importantly black hole spin.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
