T Tauri star

A T Tauri star is a young, low-mass star still contracting toward the main sequence. Its brightness and spectrum vary through magnetic activity, circumstellar material, and ongoing accretion.

Accretion disk: A rotating disk of gas and dust that spirals toward a central object under gravity. Material from this disk feeds the growing star and produces changing emission.
Pre-main-sequence star: A star that has not yet begun sustained hydrogen fusion in its core. T Tauri stars are the low-mass members of this broader evolutionary stage.
Protoplanetary disk: A rotating disk of gas and dust around a young star from which planets can form. Its evolving structure records the conditions for planet formation around T Tauri stars.
Herbig Ae/Be star: A young, intermediate-mass pre-main-sequence star with strong emission and circumstellar material. It occupies a higher-mass young-star category than T Tauri stars.
Magnetospheric accretion: A process in which a young star’s magnetic field channels disk gas onto its surface. It explains how disk material reaches the star and creates hot accretion spots.
Hayashi track: An evolutionary path along which a contracting, fully convective young star changes temperature and luminosity. It describes the early contraction followed by many low-mass T Tauri stars.
Planet formation: The process by which dust and gas around a young star assemble into planets. Observations of T Tauri disks expose the early stages of this process.
Classical T Tauri star: A T Tauri star with a substantial accretion disk and strong accretion signatures. It is the actively accreting subtype, often marked by broad emission lines.
Stellar magnetic field: The magnetic field generated by a star’s internal motion of electrically conducting plasma. Strong, changing fields drive activity and channel accretion near the stellar surface.
Protostar: A forming star still gaining mass from its surrounding molecular cloud. It precedes the T Tauri phase as collapse and major mass growth wind down.

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