NASA has discovered The M60-UCD1 by using their Hubble Space Telescope in 2013. It is considered as on of the smallest known galaxies. However, the dwarf galaxy is harboring a “monster” black hole which is discovered by the space agency.
The M60-UCD1 has a diameter of 300 light years which is about 1/500th of our galaxy’s width. but, it contains over 140 million stars which also makes it one of the densest galaxies.
NASA compared it with our nighttime sky which we used to see from Earth's surface, it contains over 4,000 stars. If we lived inside the newly-discovered M60-UCD1, our nighttime sky would be covered with at least one million stars “visible to the naked eye.”