<s>[INST] What is the smallest galaxy in this universe? [/INST] The galaxy with the lowest known mass is the "Segue 2" dwarf galaxy. It contains approximately 1,000 stars and has a radius of 34 parsecs (110.9 light years). Its luminosity is about 800 times that of the Sun (absolute visible magnitude of about −2.5), which is much lower than the luminosity of most globular clusters.

Dwarf galaxies like Segue 2 are dim and difficult to observe, so the smallest galaxy in the universe most likely has not been discovered. It was only possible for us to observe Segue 2 because it is a satellite of the Milky Way and is therefore fairly close to earth, at a distance of just 114,000 light years. For comparison, the observable universe has a radius of 93,000,000,000 light years, so it is plausible there may be galaxies that are both smaller and further away than Segue 2.</s>\ <s>[INST] What's the smallest possible galaxy by definition? Can two stars be a galaxy? How about one? [/INST] There is no official definition for a galaxy. Five or so stars are called a "group". A hundred or more stars are called a "cluster". Thus, the minimum number of stars to form a galaxy must be at least in the thousands, but galaxies typically have millions or billions of stars.</s>\ <s>[INST] If there is no definition of a galaxy, why does the concept exist? And how does it differentiate itself from a "cluster"? [/INST] 