What type of stars are T Tauri stars classified as?

T Tauri stars are classified as pre-main-sequence variable stars. These stars are in an early stage of stellar evolution, where they are still forming and have not yet reached the stable hydrogen-burning phase of the main sequence. The classification stems from their variability, which is characterized by changes in brightness due to factors such as surface phenomena and accretion processes, where they accumulate material from their surrounding protoplanetary disks.

This distinctive stage of evolution is crucial for understanding the formation of stars and planetary systems, as T Tauri stars represent the transition from a dense cloud of gas and dust to a fully developed star. The mechanisms that cause their variability help astronomers learn more about stellar development and the conditions present in nascent systems.

In contrast, the other classifications do not apply to T Tauri stars. They are not post-main-sequence stars, which have already exhausted their hydrogen fuel and are transitioning to later stages of evolution. They also do not fall under supernova remnants, which are the remnants of massive stars that have exploded, nor are they red giant stars, which are large, expanded stars in a late stage of evolution after the main sequence.