Those stars which belong to the spherical halo surrounding our Galaxy and others. Such stars have a low content of heavy elements, belong to Population II, and are believed to be older than most stars in the galactic disk, such as the Sun. Some are found within the disk but are simply in transit through it on their elongated orbits around the galactic centre, and can easily be distinguished by their high velocities with respect to the disk stars (see high-velocity star).