A rare class of pre-main-sequence object which appears to be coupled with cometary globules; abbr. FU. They are also known as fuors or FUOrs. Most probably they consist of a T Tauri-like star surrounded by a very luminous accretion disk currently in a state of very high mass accretion (approx. 10−4 solar masses per year). FU Orionis stars exhibit a gradual rise of up to 6 magnitudes over several months, accompanied by mass ejection. The star subsequently remains constant or shows a slight decline over a period of years or decades, in contrast to the much shorter timescales in the related EX Lupi stars.
Subjects: Astronomy and Astrophysics.