[Paper Review] From Bubbles and Filaments to Cores and Disks: Gas Gathering and Growth of Structure Leading to the Formation of Stellar Systems

J. E. Pineda, D. Arzoumanian+9 more|arXiv (Cornell University)|May 8, 2022

Astrophysics and Star Formation StudiesPhysics and Astronomy11 references37 citations

TL;DR

The paper synthesizes multi-scale observations and simulations to present a coherent, anisotropic growth picture of interstellar structures from giant bubbles to protostellar disks, linking gas gathering and hierarchical accretion to star and disk formation.

ABSTRACT

The study of the development of structures on multiple scales in the cold interstellar medium has experienced rapid expansion in the past decade, on both the observational and the theoretical front. Spectral line studies at (sub-)millimeter wavelengths over a wide range of physical scales have provided unique probes of the kinematics of dense gas in star-forming regions, and have been complemented by extensive, high dynamic range dust continuum surveys of the column density structure of molecular cloud complexes, while dust polarization maps have highlighted the role of magnetic fields. This has been accompanied by increasingly sophisticated numerical simulations including new physics (e.g., supernova driving, cosmic rays, non-ideal magneto-hydrodynamics, radiation pressure) and new techniques such as zoom-in simulations allowing multi-scale studies. Taken together, these new data have emphasized the anisotropic growth of dense structures on all scales, from giant ISM bubbles driven by stellar feedback on $\sim$50-100 pc scales through parsec-scale molecular filaments down to $<$0.1 pc dense cores and $<$1000 au protostellar disks. Combining observations and theory, we present a coherent picture for the formation and evolution of these structures and synthesize a comprehensive physical scenario for the initial conditions and early stages of star and disk formation.

Motivation & Objective

• Motivate understanding of star formation inefficiency and the origin of the IMF by tracing structure growth across scales in the cold ISM.
• Synthesize observations (spectral lines, dust continuum, polarization) with advanced HD/MHD simulations to connect bubbles, filaments, cores, and disks.
• Clarify how expanding bubbles, filament formation, and anisotropic accretion contribute to initial conditions for star and disk formation.

Proposed method

• Reviews multi-scale observational data from HI shells, H II regions, filaments, cores, and disks.
• Integrates state-of-the-art HD and MHD simulations including feedback, non-ideal MHD, and zoom-in techniques to study multi-scale structure growth.
• Discusses formation mechanisms of filaments in shock-compressed layers and their evolution via gravity-driven accretion.

Figure 1: Color composite image showing the H i emission at 7.4 $\rm km\,s^{-1}$ (red) and at 3.3 $\rm km\,s^{-1}$ (blue) and the column density map derived from combined Herschel + Planck data (green). The white circles trace the two H i shells associated with the Corona Australis (CrA) molecular c

Experimental results

Research questions

• RQ1 How do expanding interstellar bubbles influence the formation and shaping of filamentary molecular clouds?
• RQ2 What are the dominant filament formation mechanisms in shock-compressed layers, and how do they feed dense cores and eventually protostellar disks?
• RQ3 How does anisotropic gas accretion connect structures from large (≥50–100 pc) to small (<0.1 pc) scales and drive star/disk formation?

Key findings

• Dense structures grow anisotropically across scales from bubbles to filaments to cores to disks.
• Gas accretion proceeds in a hierarchical flow: shell-like accretion from bubbles to filaments, axial contraction from filaments to cores, and non-axisymmetric accretion through streamers from cores to disks.
• Filament formation in shock-compressed layers is dominated by type-O and type-C mechanisms at higher shock velocities, producing filaments with line masses resembling observed Salpeter-like distributions.
• Filaments accrete mass and evolve from subcritical to supercritical regimes, with gravity-driven accretion sustaining growth after initial formation.
• Observations of velocity gradients and magnetic field orientations support anisotropic gas accretion along and into filaments and hubs, consistent with the proposed multi-scale growth paradigm.

Figure 2: a) Illustration of a generic bipolar H ii region and its environment. The ionized gas, the molecular gas, and the PAH emission of the PDR are shown in red, blue, and grey, respectively. b) Composite image of G $319.88+00.79$ , which is an observed example of a bipolar H ii region. c) Cente