Emergence of high-mass stars in complex fiber networks (EMERGE)

V. From filaments to spheroids: the origin of the hub-filament systems

¹ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
² Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
³ Department of Astronomy, Harvard University, 60 Garden St., Cambridge, MA 02138, USA
⁴ University of Cologne, I. Physical Institute, Zülpicher Str. 77, 50937 Cologne, Germany
⁵ Department of Physics, Stanford University, Stanford, CA 94305, USA
⁶ Kavli Institute for Particle Astrophysics & Cosmology, PO Box 2450, Stanford University, Stanford, CA 94305, USA
⁷ Universitäts-Sternwarte, Ludwig-Maximilians-Universität München, Scheinerstrasse 1, 81679 Munich, Germany
⁸ Excellence Cluster ORIGINS, Boltzmannstrasse 2, 85748 Garching, Germany
⁹ Max-Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
¹⁰ Istituto di Astrofisica e Planetologia Spaziali (INAF-IAPS), Via Fosso del Cavaliere 100, 00133, Rome, Italy
¹¹ Chalmers University of Technology, Department of Space, Earth and Environment, 412 93 Gothenburg, Sweden
¹² SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK

^★ Corresponding author; alvaro.hacar@univie.ac.at

Received: 18 May 2024
Accepted: 7 November 2024

Abstract

Context. Identified as parsec-size, gas clumps at the junction of multiple filaments, hub-filament systems (HFS) play a crucial role during the formation of young clusters and high-mass stars. These HFS still appear to be detached from most galactic filaments when compared in the mass–length (M–L) phase space.

Aims. We aim to characterize the early evolution of HFS as part of the filamentary description of the interstellar medium (ISM).

Methods. Combining previous scaling relations with new analytic calculations, we created a toy model to explore the different physical regimes described by the M–L diagram. Despite its simplicity, our model accurately reproduces several observational properties reported for filaments and HFS, such as their expected typical aspect ratio (A), mean surface density (Σ), and gas accretion rate (ṁ). Moreover, this model naturally explains the different mass and length regimes populated by filaments and HFS, respectively.

Results. Our model predicts a dichotomy between filamentary (A ≥ 3) and spheroidal (A < 3) structures connected to the relative importance of their fragmentation, accretion, and collapse timescales. Individual filaments with low accretion rates are dominated by an efficient internal fragmentation. In contrast, the formation of compact HFS at the intersection of filaments triggers a geometric phase-transition, leading to the gravitational collapse of these structures at parsec-scales in ~1–2 Myr. In addition, this process also induces higher accretion rates.