Prestars

Prestars are dense, cold condensations within molecular clouds that represent an early stage in star formation. They are gravitationally bound objects that have not yet formed a central protostar and therefore lack significant internal energy output. Typical prestellar cores have temperatures around 8–12 K and hydrogen molecule densities of 10^4–10^5 cm^-3. They are primarily identified by their faint or absent infrared emission and by submillimeter dust continuum radiation, as well as by molecular line tracers such as N2H+ and NH3 that indicate high density and low turbulence.

Formation and evolution: Prestars arise through the fragmentation and contraction of larger cloud structures under gravity, aided by external pressure and dynamical processes in molecular clouds. A prestellar core becomes a protostar when a central object forms and begins to accrete material, marking the transition to a protostellar core (often classified as Class 0). The prestellar phase is typically brief on cosmic timescales, spanning a few hundred thousand years in many regions.

Observational significance: Studying prestars informs theories of core formation, the initial mass function, and the timescales of early star formation. Because they lack internal heating, their detection relies on cold dust emission and dense-gas tracers, making them useful probes of the earliest, pre-accretion stages of stellar birth.