The term dark galaxy is used for the concept of an object like a galaxy except with no stars, i.e., a dark matter halo with some gas clouds (hydrogen) and/or dust. Such an object should be detectable through gravitational lensing. Some would use the term even for such an object with stars if they produce no observable EMR. Theories have been developed of regarding origins and characteristics. Some objects are proposed as candidates (one being the Smith Cloud), but no object has consensus acceptance.