Star Formation Efficiency

The efficiency with which gas within dark matter halos is converted into stars — the ratio of stellar mass to available baryonic mass — is observed to be low across all environments, typically a few percent globally and only reaching ~20–30% even in the most efficient halos. Standard ΛCDM requires a combination of supernova feedback, AGN feedback, cosmic ultraviolet background suppression, and ram pressure stripping to simultaneously explain why star formation efficiency is low everywhere and why it varies systematically with environment. The combination of feedback mechanisms required is complex, difficult to calibrate from first principles, and sometimes requires conflicting parameter choices to match different observational constraints simultaneously. Successive Collision Theory provides a primary regulator of star formation efficiency through angular momentum inheritance: the centrifugal barrier established by the inherited specific angular momentum prevents rapid radial infall of gas to the star-forming dense core, setting the baseline efficiency at a low value without requiring fine-tuned feedback.

The angular momentum barrier operates at every level of the nested frame hierarchy, from the largest supercluster scales down to the scale of individual molecular clouds within galaxies. At each level, the specific angular momentum inherited from the level above sets the centrifugal support of the gas, requiring it to lose angular momentum through gravitational torques or viscosity before collapsing to higher density. This angular momentum transfer process is intrinsically slow — it is limited by the dynamical timescale of the orbit rather than the free-fall time — which naturally suppresses the global star formation efficiency well below unity. Environmental variation in star formation efficiency then reflects variation in the local angular momentum inheritance: collision nodes received higher angular momentum deposition than the void interiors, making node-region galaxies more rotationally supported and potentially more efficient in some mass ranges, while void-region galaxies have lower angular momentum and lower efficiency. Feedback processes in SCT modulate this baseline but are not its primary determinant.