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).