an earlier time of the universe. Intermediate population II stars are common in the bulge near the center of the Milky Way, whereas Population II stars found in the galactic halo are older and thus more metal-poor. Globular clusters also contain high numbers of population II stars. In 2014, the first planets around a halo star were announced around Kapteyn's star, the nearest halo star to Earth, around 13 light years away. However, later research suggests that Kapteyn b is just an artefact of stellar activity and that Kapteyn c needs more study to be confirmed. The metallicity of Kapteyn's star is estimated to be about 8 times less than the Sun. Different types of galaxies have different histories of star formation and hence planet formation. Planet formation is affected by the ages, metallicities, and orbits of stellar populations within a galaxy. Distribution of stellar populations within a galaxy varies between the different types of galaxies. Stars in elliptical galaxies are much older than stars in spiral galaxies. Most elliptical galaxies contain mainly low-mass stars, with minimal star-formation activity. The distribution of the different types of galaxies in the universe depends on their location within galaxy clusters, with elliptical galaxies found mostly close to their centers. See also Protoplanetary disk List of exoplanets List of multiplanetary systems Notes References Further reading Concepts in astronomy