hundreds of billions of stars, and there are more than 2 trillion (1012) galaxies. Overall, there are as many as an estimated 1×1024 stars (more stars than all the grains of sand on planet Earth). While it is often believed that stars only exist within galaxies, intergalactic stars have been discovered.A multi-star system consists of two or more gravitationally bound stars that orbit each other. The simplest and most common multi-star system is a binary star, but systems of three or more stars are also found. For reasons of orbital stability, such multi-star systems are often organized into hierarchical sets of binary stars. Larger groups called star clusters also exist. These range from loose stellar associations with only a few stars, up to enormous globular clusters with hundreds of tho