What adverse effect occurs if a collapsing core cannot efficiently radiate away converted gravitational energy?

The rising thermal pressure will halt the collapse locally.

During gravitational contraction, gravitational potential energy is continuously converted into thermal energy, causing the core's temperature to rise significantly. For the cascade of star formation to proceed—allowing the collapse to progress to smaller and smaller scales—this generated heat must be radiated away efficiently, primarily through molecular line emission. If the cooling mechanism fails or is too slow relative to the rate of collapse, the accumulating heat leads to a rapid spike in thermal pressure. This excessive outward thermal pressure can then counterbalance the still-increasing gravitational force, causing a local halting of the contraction and potentially resulting in the formation of larger, less dense stellar remnants instead of smaller stars.