Protostar

A protostar is a young forming star that grows by accreting gas and dust from its surroundings before sustained nuclear fusion begins in its core.

Gravitational collapse: The inward contraction of matter under gravity, often triggered when pressure cannot support a cloud. It begins the dense, central condensation that develops into a protostar.
Molecular cloud: A cold, dense interstellar cloud composed mainly of molecular hydrogen, with dust and other molecules. Protostars form in the densest regions of these clouds.
Infrared astronomy: The study of celestial objects through infrared radiation, which can pass through some intervening dust. Infrared observations reveal protostars hidden inside dense, dusty clouds.
Prestellar core: A dense, gravitationally bound region of a molecular cloud that has not yet formed a central protostar. It precedes protostellar formation and lacks a central accreting object.
Accretion disk: A rotating disk of gas and dust that spirals toward a central object while transferring angular momentum outward. It channels cloud material onto the protostar and redistributes angular momentum.
Jeans instability: The gravitational instability that causes a gas cloud to collapse when its mass exceeds a critical value. It describes when a cloud region can begin collapsing toward protostellar formation.
Spectral energy distribution: The measured energy emitted by an object across a range of wavelengths. Its infrared excess helps identify embedded protostars and estimate their properties.
T Tauri star: A young, low-mass star whose strong activity and variability mark an early stage of stellar evolution. It is a later young-star stage, typically after the main protostellar accretion phase.
Bipolar outflow: A pair of oppositely directed jets or winds launched from a young stellar system. Outflows expel some infalling gas and help regulate the protostar’s growth.
Angular momentum: A measure of rotational motion conserved in an isolated physical system. Conservation of angular momentum helps make infalling protostellar gas form a disk.

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