Oscillating Filaments: I - Oscillation and Geometrical Fragmentation

TL;DR

This paper investigates how slight bends in filaments can induce oscillations leading to fragmentation at any scale, revealing a new 'geometrical fragmentation' process that challenges previous scale limitations.

Contribution

It introduces the concept of geometrical fragmentation caused by oscillations in bent filaments, supported by analytical derivations and simulation results.

Findings

Oscillations trigger fragmentation in bent filaments.

Fragmentation scale matches sinusoidal perturbation wavelength.

Oscillation patterns can obscure core infall signatures.

Abstract

We study the stability of filaments in equilibrium between gravity and internal as well as external pressure using the grid based AMR-code RAMSES. A homogeneous, straight cylinder below a critical line mass is marginally stable. However, if the cylinder is bent, e.g. with a slight sinusoidal perturbation, an otherwise stable configuration starts to oscillate, is triggered into fragmentation and collapses. This previously unstudied behavior allows a filament to fragment at any given scale, as long as it has slight bends. We call this process `geometrical fragmentation'. In our realization the spacing between the cores matches the wavelength of the sinusoidal perturbation, whereas up to now, filaments were thought to be only fragmenting on the characteristical scale set by the mass-to-line ratio. Using first principles, we derive the oscillation period as well as the collapse timescale analytically. To enable a direct comparison with observations, we study the line-of-sight velocity for different inclinations. We show that the overall oscillation pattern can hide the infall signature of cores.