Protostellaire

Protostellaire is a French term meaning protostellar, referring to the early stages of star formation. It describes a dense condensation of gas and dust within a molecular cloud that is collapsing under its own gravity. During this phase, commonly called the protostellar phase, the core accretes material from its surroundings through an accretion disk while launching bipolar outflows and jets that help remove angular momentum.

The evolution from a prestellar core to a protostar is divided into several classes based on the spectral energy distribution and the amount of circumstellar material. Class 0 protostellar objects are deeply embedded and emit primarily in the far‑infrared and submillimetre, whereas Class I sources become increasingly visible in the near‑infrared as the envelope thins. By the Class II stage, the protostar has largely shed its envelope, revealing a pre‑main sequence star surrounded by a protoplanetary disk.

Radiation from the protostar heats the surrounding envelope, creating a temperature gradient that can be studied through multi‑wavelength observations. Molecular line emission, such as that from CO, traces the kinematics of outflows and infall, while dust continuum emission provides mass estimates. The protostellar phase typically lasts a few hundred thousand years, encompassing much of the mass accretion process that determines the final stellar mass.

Studying protostellar objects is essential for understanding how stars like the Sun form, how planetary systems assemble, and how feedback from early stellar activity shapes the interstellar medium. Advanced telescopes—ALMA, the James Webb Space Telescope, and future radio arrays—continue to refine our knowledge of protostellar physics, revealing detailed structures in the accretion disks and the earliest signs of planet formation within these nascent stellar systems.