As an expert in astrophysics, I can tell you that the term "star" typically refers to a massive celestial object that generates energy through nuclear fusion. However, the concept of the "smallest star" is a bit misleading because stars can vary greatly in size, and the smallest known stars are not significantly smaller than the largest known stars in the same category (main sequence stars, for example).

The smallest known main sequence stars are red dwarfs, and the smallest known red dwarf is EBLM J0555-57Ab, which is about 8.4 Jupiter masses and has a radius of about 0.797 times that of the Sun. It's important to note that there are even smaller stellar objects known as brown dwarfs, which are not massive enough to sustain hydrogen fusion and are often referred to as "failed stars." The smallest known brown dwarf is WISE 0855−0714, which is about 3 to 10 times the mass of Jupiter.

To answer your question directly: The smallest known main sequence star is EBLM J0555-57Ab, and the smallest known brown dwarf is WISE 0855−0714.

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Currently the smallest star we have found is called OGLE-TR-122b. This star is around 96 times more massive than Jupiter. We call this type of star a red dwarf. The other side to this answer involves a star that is at the very end of its life.read more >>