Jets and Outflows from Star to Cloud: Observations Confront Theory

Abstract

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). In describing these observations we also look to the future and consider the questions that new facilities such as ALMA and the Jansky Array can address. 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.

The jet feedback mechanism (JFM) in stars, galaxies and clusters

“…Feedback in star forming clouds is reviewed by, e.g., Vázquez-Semadeni (2011), Frank et al (2014), Krumholz et al (2014), and Dale (2015). The feedback during star cluster formation is likely to explain the inefficient process of star formation (e.g.…”

“…Jets can remove some mass from the cloud in which the stars are forming, and can increase somewhat the turbulence in the cloud (e.g., Frank et al 2014 and references therein). As with the process of bubbleinflation, a relative transverse motion between the jets and the ambient gas increases the efficiency of momentum transfer from the jets to the ambient gas (Frank et al 2014). Federrath et al (2014) simulated the feedback from jets and outflows in star cluster formation.…”

“…This review does not deal with jet-launching processes nor with the general properties of jets and their relation to accretion disks. These topics are reviewed and studied in many other papers where more references can be found (e.g., Mirabel & Rodríguez 1999;Fender & Belloni 2004;Ferreira et al 2006;Livio 2011;Fender & Belloni 2012;Pudritz et al 2012;McKinney et al 2013;Zanni & Ferreira 2013;Frank et al 2014;Lasota et al 2014;Lovelace et al 2014;McKinney et al 2014). I assume that whenever the accreted gas has a large enough specific angular momentum jets are launched.…”

The Gas Disk: Evolution and Chemistry

“…Cleeves et al 2015). The second mechanism leads to fast jets and associated molecular outflows, but here the acceleration mechanism of disk material along magnetic fields is poorly understood, and it is also still a matter of debate whether the launching mechanism of molecular outflows is directly associated with jet acceleration (see review of Frank et al 2014). The other processes (turbulence, winds and instabilities) are sensitive to heating and cooling processes in the disk.…”

“…6 of this book and the review of Alexander et al 2014). In the T Tauri phase, mass-loss rates in outflows/jets and photoevaporative winds amount to no more than about 10 % of the stellar accretion rate (Hartigan et al 1995;Cabrit 2002;Frank et al 2014). However, in late evolutionary phases the photoevaporation rate may locally (at distances of several au from the star) exceed the disk accretion rate, which leads to the rapid formation of a gap and the subsequent erosion of the entire disk on time scales of only a few hundred kyr or ≈10 % of the disk lifetime.…”