T Tauri

T Tauri stars are a class of stars thought to represent extremely young pre-main sequence stars, in an early stage of life. They are seen near many molecular clouds in our galaxy. The first ones were found in 1945, identified by their optical variability and strong chromospheric lines.

T Tauri stars have masses and temperatures similar to the Sun, but are significantly brighter. They have fast rotation rates, typically with a period of a few days, compared to a month for the Sun, and are very active and variable. There is evidence of large areas of starspot coverage, and they have intense and variable X-ray and radio emissions (approximately 1000 times that of the Sun). Many have extremely powerful stellar winds. T Tauri stars have more lithium than the Sun, an element which is easily destroyed at "low" core temperatures (1,000,000 K). It is thought that most of a T Tauri's energy is derived from gravitational collapse, with its core not yet hot enough for proton-proton fusion (2,500,000 K).

Roughly half of T Tauri stars have circumstellar disks, which may be remnants of the solar nebula which formed them. Most T Tauri stars are in binary star systems. In various stages of their life, they are called Young Stellar Objects (YSOs).