Modification to the Jeans criterion by external tides: anisotropic fragmentation and formation of filaments

• Published in: Monthly notices of the Royal Astronomical Society Vol. 532; no. 1; pp. 1126 - 1128
• Main Author: Li, Guang-Xing
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01.07.2024
• Subjects: Criteria; Filaments; Fragmentation; Gravitational collapse; Tides; methods: analytical; ISM: clouds; galaxies: star formation
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stae900

ABSTRACT The Jeans criterion sets the foundation of our understanding of gravitational collapse. Jog studied the fragmentation of gas under external tides and derived a dispersion relation $l^{\prime } = l_{\rm Jeans} \frac{1}{(1 + \lambda _0^{\prime } / 4 \pi G \rho _0)^{1/2}} \,\,.$ She further concludes that the Jeans mass is $m_{\rm incorrect}^{\prime }=m_{\rm Jeans} [1/(1 + \lambda _0^{\prime } / 4 \pi G \rho _0)^{3/2}]$. We clarify that due to the inhomogeneous nature of tides, this characteristic mass is incorrect. Under weak tides, the mass is $m \approx \rho \, l_1 l_2 l_3$, where the modifications to Jeans lengths along all three dimensions need to be considered; when the tide is strong enough, collapse can only occur once 1 or 2 dimensions. In the latter case, tides can stretch the gas, leading to the formation of filaments.