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

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 = lJeans 1(1 + λ ₀ / 4 π G ρ ₀)1/2 \,\,. She further concludes that the Jeans mass is mincorrect=mJeans [1/(1 + λ ₀ / 4 π G ρ 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 ≈ ρ \, l₁ l₂ l₃, 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.