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.
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