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<jats:title>Abstract</jats:title> <jats:p>With the aim of characterizing the dynamical processes involved in the formation of young protostars, we present high-angular-resolution ALMA dust polarization observations of the Class 0 protostellar cores Serpens SMM1, Emb 8(N), and Emb 8. With spatial resolutions ranging from 150 to 40 au at 870 <jats:italic>μ</jats:italic>m, we find unexpectedly high values of the polarization fraction along the outflow cavity walls in Serpens Emb 8(N). We use 3 mm and 1 mm molecular tracers to investigate outflow and dense-gas properties and their correlation with the polarization. These observations allow us to investigate the physical processes involved in the radiative alignment torques (RATs) acting on dust grains along the outflow cavity walls, which experience irradiation from accretion processes and outflow shocks. The inner core of SMM1-a presents a polarization pattern with a poloidal magnetic field at the bases of the two lobes of the bipolar outflow. To the south of SMM1-a we see two polarized filaments, one of which seems to trace the redshifted outflow cavity wall. The other may be an accretion streamer of material infalling onto the central protostar. We propose that the polarized emission we see at millimeter wavelengths along the irradiated cavity walls can be reconciled with the expectations of RAT theory if the aligned grains present at &lt;500 au scales in Class 0 envelopes have grown larger than the 0.1 <jats:italic>μ</jats:italic>m size of dust grains in the interstellar medium. Our observations allow us to constrain the magnetic field morphologies of star-forming sources within the central cores, along the outflow cavity walls, and in possible accretion streamers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A Steady Electron Runaway Model (SERM) is formulated describing plasmas in the astrophysical “condition” having finite (rather than infinitesimal) Knudsen number, <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{K}}}_{\mathrm{Pe}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, suggesting an omnipresent leptokurtic, nonthermal, and heat-conducting electron velocity distribution function (eVDF) as the replacement for the Maxwellian ansatz typically made. The shape parameters of SERM’s eVDFs are functionals of the local dimensionless electric field, <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{E}}}_{\parallel }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, shown to be nearly interchangeable with the pressure Knudsen number, <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{K}}}_{\mathrm{Pe}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>. The eVDF is determined by the total density and pressure, heat flux, and <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{E}}}_{\parallel }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> with the Maxwellian as a special case when <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{E}}}_{\parallel }=0$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>. The nonthermal part of the eVDF is caused by local and global runaway physics and its density fraction is monotonically dependent on <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{E}}}_{\parallel }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>. SERM explains the distinguishable conduction band of suprathermal electrons to be the result of the inhomogeneities of astroplasmas that require <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{E}}}_{\parallel }\ne 0$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn7.gif" xlink:type="simple" /> </jats:inline-formula> to enforce quasi-neutrality. SERM shows that the direction of the heat flow should be that of <jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{\parallel }\hat{{\boldsymbol{b}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn8.gif" xlink:type="simple" /> </jats:inline-formula>. Almost all reported space age correlations among the shape parameters of the solar wind eVDF are reproduced by this modeling, including scaling of: (i) nonthermal spectral break energy, and (ii) partition of suprathermal density and partial pressure, with solar wind speed. SERM, together with eVDF observations, indirectly bracket <jats:inline-formula> <jats:tex-math> <?CDATA $0.2\lt {{\mathbb{E}}}_{\parallel }(1\,\mathrm{au})\lt 0.65$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn9.gif" xlink:type="simple" /> </jats:inline-formula>, producing a steady-state eVDF, consistent with in situ (i) heat flows, (ii) <jats:italic>strahl</jats:italic> pitch angle features in high-speed winds, (iii) <jats:inline-formula> <jats:tex-math> <?CDATA ${J}_{\parallel }=0$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn10.gif" xlink:type="simple" /> </jats:inline-formula>, and (iv) non-negative probability at <jats:italic>all</jats:italic> velocities. Because finite <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{K}}}_{\mathrm{Pe}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn11.gif" xlink:type="simple" /> </jats:inline-formula> is the identified prerequisite for SERM modeling, nonthermal eVDF’s are expected nearly everywhere in astrophysics where <jats:inline-formula> <jats:tex-math> <?CDATA ${{\mathbb{K}}}_{\mathrm{Pe}}\gt 0.01$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4882ieqn12.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>