The FU Orionis variables - FUOrs for short - are eruptive variable stars in regions of star formation. In less than one year, a typical FUor brightens by a factor of ten or more. The system takes several decades (sometimes centuries) to return to its pre-outburst brightness.

Compared to other young stars, FUors have some special features. They are always associated with reflection nebulae; many have outflows and Herbig-Haro objects. FUors also have unusual spectra which show that the source of the eruption is a circumstellar disk not a star.

After reading an amazing review by George Herbig, Lee Hartmann and I began to study FUors in the mid-1980's. We were the first to show that FUors have a luminous accretion disk. During a FUor eruption, the disk brightens and drives a powerful wind that eventually becomes an HH object.

FUors are a small, but important research area in star formation. During the past two decades, more have been discovered. We have also learned more about their disks and outflows. The links below provide summaries of recent work on FUors.