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Earth and Space Sciences · Glossary

What is Protostar?

Definition 1.8 University Earth and Space Sciences — Year 2 · Chapter 1 — The Interstellar Medium and Star Formation

A protostar is a star in formation that is still gaining most of its mass by accretion of the gas of its parent core; it shines by the energy that the falling gas releases, not by nuclear fusion.

From a dense core to a planetary system (schematic, not to scale). (1) A cold core near the Jeans mass. (2) Its centre collapses first and a protostar forms. (3) The protostar grows by accretion through a disc, while a bipolar outflow clears gas along the rotation axis. (4) The envelope gone, a T Tauri star, still contracting, is surrounded by its disc. (5) The disc has dispersed; what remains of its solids are planets. Times from the free-fall and accretion estimates of the text and from the disc lifetimes of the last section.
From a dense core to a planetary system (schematic, not to scale). (1) A cold core near the Jeans mass. (2) Its centre collapses first and a protostar forms. (3) The protostar grows by accretion through a disc, while a bipolar outflow clears gas along the rotation axis. (4) The envelope gone, a T Tauri star, still contracting, is surrounded by its disc. (5) The disc has dispersed; what remains of its solids are planets. Times from the free-fall and accretion estimates of the text and from the disc lifetimes of the last section.
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