prompter: What is the smallest galaxy in this universe?

assistant: It is impossible to know the smallest galaxy in the universe. However, one of the smallest we have found is the Segue 2 Dwarf Galaxy, according to Wikipedia.

prompter: How are galaxies created?

assistant: Galaxies are formed through a process of gravitational collapse, where large clouds of gas and dust begin to condense and collapse in on themselves. As the clouds become denser, they begin to form stars, and these stars are eventually pulled together into rotating disk-like structures called galaxies.

The process of galaxy formation is thought to have begun in the early universe, shortly after the Big Bang. As the universe expanded and cooled, small fluctuations in the distribution of matter caused regions of the universe to become denser. These dense regions then became the seeds for the formation of galaxies.

Over time, the gravitational attraction between the clouds of gas and dust caused them to merge and grow, eventually forming the large spiral and elliptical galaxies we see today. The process of galaxy formation and evolution is still not fully understood, and is an active area of research in astrophysics.

It's believed that galaxies continue to evolve and change over time, through processes such as merging with other galaxies, the formation of new stars, and the movement of stars and gas within the galaxy.

assistant: Galaxies are formed out of large amount of gases. They collapses and rotate on for the formation.

assistant: 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.

prompter: What's the smallest possible galaxy by definition? Can two stars be a galaxy? How about one?

assistant: According to Wiktionary, Galaxy is defined as "Any of the collections of many millions or billions of stars, galactic dust, black holes, etc. existing as independent and coherent systems, of which there are billions in the known universe," and a Dwarf Galaxy as "Any galaxy, considerably smaller than the Milky Way, that has only several billions of stars."
Since there is no official definition on size, it appears that what can be called a galaxy depends on characteristics such as orbital plane, shape, and distance from other galaxies.

assistant: 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.

prompter: If there is no definition of a galaxy, why does the concept exist? And how does it differentiate itself from a "cluster"?

assistant: 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.

assistant: The smallest known galaxy in the universe is Segue 1. Segue 1 is a dwarf galaxy that is located about 75,000 light-years from Earth in the constellation Leo. It was discovered in 2006 and is estimated to have a mass of only about 1% of the mass of the Milky Way. Despite its small size, Segue 1 is thought to contain a relatively high proportion of dark matter, which makes it an important object for the study of galaxy formation and evolution.