Gravitational collapse of dense clumps in the hub. According to Eqs. (6) and (7), to test whether the two dense clumps (LC 1 and LC 2) in the B-S HFS are in a state of gravitational collapse, we examined their velocity distributions with radius. Left panel: Velocity distribution with radius in LC 1 (l₀ = 43.17°, b₀ = 0.00°), with a fitted curve yielding a systemic velocity of 5.0 km s⁻¹. Based on the integral intensity weighted by the B-S component, we estimated the clump mass to be approximately 17997 M_⊙, with the best-fit result at 15000 M_⊙, and an inclination angle of 78° for the plane of the sky. Right panel: Velocity distribution with radius in LC 2 (l₀ = 43.17°, b₀ = −0.00°), with a fitted curve yielding a systemic velocity of 4.5 km s⁻¹. Based on the integral intensity weighted by the B-S component, we estimate the clump mass to be approximately 9098 M_⊙, with the best-fit result at 10000 M_⊙, and an inclination angle of 78° concerning the plane of the sky.