<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] The smallest possible galaxy, by definition, is a single star. This is because, while galaxies are large collections of stars, they also have enough mass to hold them together via their own gravity. A single star, therefore, is not massive enough to be considered a galaxy.

However, two stars can be a galaxy. This is because two stars have enough mass to form a gravitational bond that would keep them bound together, and thus form a galaxy. This is known as a binary star system. In a binary star system, the two stars orbit around each other, and this can appear as a single, bright point of light from far away.</s>