prestellar

Prestellar describes a stage in star formation that precedes the emergence of a protostar. In astronomy, prestellar cores are compact, dense regions within molecular clouds that are gravitationally bound and expected to collapse to form stars. They represent the immediate precursors to protostellar objects and are distinguished from more evolved stages by the absence of an internal heating source.

Physical properties of prestellar cores typically include very low temperatures, around 8–12 K, and high densities on the order of 10^4–10^5 cm^-3. They are small in size, commonly about 0.01–0.1 parsec across, and contain roughly a fraction to a few solar masses of material. The cores are susceptible to gravitational instability, often described by the Jeans criterion, and external factors such as turbulence or magnetic fields can influence their evolution and collapse timescales, which are typically around a few times 10^5 years.

Evolution within a prestellar core involves gradual contraction under gravity. As density increases, a central region may form a first hydrostatic core, followed by the development of a true protostar once rapid accretion begins. Throughout this phase, the core remains largely devoid of internal radiation, which helps to distinguish it from protostellar objects in observations.

Observationally, prestellar cores are studied through cold dust continuum emission in the submillimeter and millimeter regimes and through molecular line tracers such as N2H+ and NH3. They often show evidence of CO depletion onto dust grains and lack a central infrared source. Notable examples include cores in nearby molecular clouds such as L1544 in Taurus.

The study of prestellar cores informs models of star formation, core fragmentation, and the origin of the stellar initial mass function, shedding light on the earliest conditions that lead to star birth.