What is the smallest star in the universe?

As of May 2015, the smallest known star in the universe is 2MASS J05233822-1403022. This star has a brightness that is 1/8,000 the brightness of the sun. Its diameter is 0.09 times that of the sun, making it smaller than Jupiter.

2MASS J05233822-1403022 is relatively close to the Earth, at approximately 40 light years away. However, it is too faint to be seen without a strong telescope. The star is also one of the coolest and least massive of the known stars. It was first observed as part of the Two Micron All-Sky Survey, which was conducted at Cal Tech to scan the entire sky. The star is considered a very low-mass red dwarf, as of 2015.