Stability of Filaments in Star-Forming Clouds and the Formation of Prestellar Cores in Them

Abstract

The exact process(es) that generate(s) dense filaments which then form prestellar cores within them is unclear. Here we study the formation of a dense filament using a relatively simple set-up of a pressure-confined, uniform-density cylinder. We examine if its propensity to form a dense filament and further, to the formation of prestellar cores along this filament, bears on the gravitational state of the initial volume of gas. We report a radial collapse leading to the formation of a dense filamentary cloud is likely when the initial volume of gas is at least critically stable (characterised by the approximate equality between the mass line-density for this volume and its maximum value). Though self-gravitating, this volume of gas, however, is not seen to be in free-fall. This post-collapse filament then fragments along its length due to the growth of a Jeans-like instability to form prestellar cores. We suggest dense filaments in typical star-forming clouds classified as gravitationally super-critical under the assumption of: (i) isothermality when in fact, they are not, and (ii) extended radial profiles as against pressure-truncated, that significantly over-estimates their mass line-density, are unlikely to experience gravitational free-fall. The radial density and temperature profile derived for this post-collapse filament is consistent with that deduced for typical filamentary clouds mapped in recent surveys of nearby star-forming regions.

On filament fragmentation and the impact of ambient environment on it

“…As was shown in the case of a purely thermally supported filament by Anathpindika & Freundlich (2015), a turbulence-supported filament also contracts in a quasistatic manner to acquire a peak central density, but never enters runaway collapse. Plots on various panels of Fig.…”

“…According to analytic estimates, this length is the scale over which filaments acquire a quasi equilibrium structure at an external pressure on the order of a few times 10 4 K cm −3 (Fischera & Martin 2012). An alternative explanation to the filament width relies on the thermodynamic equilibrium achieved by the filament with the external medium and thus ties the characteristic width to the local thermal Jeans length (e.g., Anathpindika & Freundlich 2015;Hocuk et al 2016). These arguments, however, ought to be revisited in view of the plots on the various panels of Fig.…”

Measuring the filamentary structure of interstellar clouds through wavelets

“…More massive filaments will undergo radial collapse, finally leading to fragmentation and star-formation (see e.g. discussion in Anathpindika & Freundlich 2015).…”

Bipolar H II regions

“…A growing body of evidence indicates that interstellar sheets and filaments play a vital role in the star formation process (e.g. André et al 2014;Anathpindika & Freundlich 2015), including the formation of massive stars (e.g. Hill et al 2011;Motte et al 2018).…”