Impeding Turbulence Decay in Self-gravitating Cloud Cores

Turbulence governs the fragmentation of molecular clouds and plays a pivotal role in star formation. The persistence of observed cloud turbulence suggests it does not decay significantly within the turnover timescale, implying a recurrent driving mechanism. Although ubiquitous self-gravity is a plausible driver, previous magnetohydrodynamic (MHD) simulations demonstrated that self-gravity alone does not modify the global turbulence decay rate.

This research provides a fresh look at how turbulence decays in star-forming regions. By running advanced simulations, the team demonstrated a crucial distinction between the macroscopic cloud and the microscopic cores within it. They found that while the dominant diffuse volume of a cloud dictates its overall decay rate, individual dense cores can maintain near-zero decay rates.

The analysis reveals that the gravitational potential energy released during core formation is the key. Whether the core formation is driven primarily by self-gravity or by turbulent compression, the released potential energy is sufficient to sustain the observed turbulence levels within these individual cores.

湍流主導著分子雲的碎裂，並在恆星形成中起著關鍵作用。觀測到的雲氣湍流具有持久性，這表明它在翻轉時標（turnover timescale）內並沒有顯著衰減，這意味著存在某種反覆驅動的機制。雖然無處不在的自引力是一個合理的驅動源，但以往的磁流體動力學（MHD）模擬表明，單靠自引力並不能改變整體的湍流衰減率。

這項研究為恆星形成區中湍流的衰減方式提供了全新的視角。通過運行先進模擬，研究團隊展示了宏觀分子雲與其內部微觀雲核之間的關鍵區別。他們發現，雖然分子雲中佔主導地位的彌散區域決定了其整體的穩定衰減率，但個別的緻密雲核卻能保持接近於零的衰減率。

分析表明，在雲核形成過程中釋放的重力位能是關鍵。無論雲核的形成主要是由自引力驅動，還是由湍流壓縮驅動，釋放出的位能都足以維持這些單個雲核內觀測到的湍流水平。這項工作表明，局部自引力可以有效地將位能轉化為湍流動能。