Gravitational instability of solar prominence threads

Abstract

Context. Prominence threads are dense and cold structures lying on curved magnetic fields that can be suspended in the solar atmosphere against gravity. Aims. The gravitational stability of threads, in the absence of non-ideal effects, is comprehensively investigated in the present work by means of an elementary but effective model. Methods. Based on purely hydrodynamic equations in one spatial dimension and applying line-tying conditions at the footpoints of the magnetic field lines, we derive analytical expressions for the different feasible equilibria (se) and the corresponding frequencies of oscillation (ω). Results. We find that the system allows for stable and unstable equilibrium solutions subject to the initial position of the thread (s0), its density contrast (ρt) and length (lt), and the total length of the magnetic field lines (L). The transition between the two types of solutions is produced at specific bifurcation points that have been determined analytically in some particular cases. When the thread is initially at the top of the concave magnetic field, that is at the apex, we find a supercritical pitchfork bifurcation, while for a shifted initial thread position with respect to this point the symmetry is broken and the system is characterised by an S-shaped bifurcation. Conclusions. The plain results presented in this paper shed new light on the behaviour of threads in curved magnetic fields under the presence of gravity and help to interpret more complex numerical magnetohydrodynamics simulations about similar structures.

Coronal rain in randomly heated arcades

“…12, as the blob moves upwards, the pressure near the upper side of the blob becomes bigger, and the increase of pressure may be more obvious while falling as both the compression and the heating are working. From the statistical analysis of the velocity component along the gravity with the number densities of all blobs (see Figure 10(d)), we also find that for denser blobs, the upward motions are relatively rare and slow as they need stronger pressure gradient to resist gravity, which is in accordance with the previous simulation works (Oliver et al 2014;Martínez-Gómez et al 2020;Adrover-González et al 2021).…”

“…The condensations formed in arched loop may fall down along the loop legs in a short time and appear as coronal rain, while the condensations in a prominence may remain suspended for many hours to several days hosted by magnetic dips (e.g. Antiochos et al 1994;Jenkins & Keppens 2021;Adrover-González et al 2021).…”

Multi-Scale Variability of Coronal Loops Set by Thermal Non-Equilibrium and Instability as a Probe for Coronal Heating

“…When the cool material is far from the footpoint, the dynamics are governed by the gas pressure and gravity, and the system presents a series of stable and unstable points, of particular interest for prominence formation. This has been recently explored by Adrover-González et al (2021).…”

Numerical simulations of turbulence in prominence threads induced by torsional oscillations

“…Prominence threads are quite thin (∼0.21 Mm) and long (between ∼3.5 and 28 Mm) structures, which are believed to be embedded in much longer magnetic tubes (see, e.g., Lin et al 2005Lin et al , 2007 of lengths of the order of 100 Mm or more whose feet are rooted in the lower atmosphere (Terradas et al 2008a). Consequently, prominence threads are usually modeled as thin magnetic flux tubes with their ends fixed at the photosphere (Ballester & Priest 1989;Rempel et al 1999;Soler et al 2012;Adrover-González et al 2021;Melis et al 2023).…”