What factor is key, alongside vast size, in allowing dense clouds to maintain structural integrity over cosmic timescales?
Answer
Very cold temperatures reducing the thermal motion of particles.
The extremely cold temperatures associated with molecular clouds slow down the random thermal motion of the gas particles, allowing gravity to effectively counteract the tendency of the material to disperse over cosmic timescales.

Related Questions
What is the scientific name for the space region between stars where clouds exist?What two elements overwhelmingly compose the gas in interstellar clouds?In terms of total mass percentage, how much of the ISM mass is typically dust?What distinguishing characteristic defines Molecular Clouds compared to other ISM phases?Which specific celestial object serves as a prime, small example of a dark nebula?What physical process causes Emission Nebulae to emit their own visible light?Why do Reflection Nebulae often exhibit a blue hue?What is the primary role of cold molecular clouds in galactic evolution?Where do complex molecules, including organic building blocks, primarily form within cold interstellar clouds?If a cubic centimeter of air on Earth contains about $10^{19}$ molecules, what is the approximate particle density range in the densest interstellar clouds?What factor is key, alongside vast size, in allowing dense clouds to maintain structural integrity over cosmic timescales?