What causes a dense molecular cloud core to collapse into a protostar?

A dense molecular cloud core collapses into a protostar when it becomes gravitationally unstable. While molecular clouds are typically supported against their own gravity by internal turbulence and magnetic fields, these forces are eventually overcome, triggering a collapse.12

The process generally follows these stages:

• Instability: At some point in its evolution, a core becomes unstable and subject to gravitational collapse. Evidence suggests that the central regions of these cores collapse first.1
• Protostar Formation: As the core contracts, it forms a condensed protostar. This contraction is eventually halted by a significant buildup of thermal pressure, which occurs when the body becomes opaque and can no longer radiate away its internal heat.1
• Accretion: The protostar continues to grow by accumulating additional material from the surrounding envelope of gas and dust, which falls onto the protostar and its swirling nebular disk.12

This collapse is a fundamental step in star formation, transforming diffuse interstellar material into a dense, radiating object.1