Our home galaxy is a cosmic melting pot. While many of its stars were born in the Milky Way, many others came from outside. They were born in smaller galaxies that were captured by the Milky Way. Over time, the smaller galaxies were ripped apart, and their stars were scattered throughout the Milky Way. And one of the Sun’s close neighbors may be an example.
Kapteyn’s Star is about 13 light-years away. Only about 20 other star systems are closer. The star is about a third the size and mass of the Sun. Don’t try looking for it, though — it’s only one percent of the Sun’s brightness, so you need a telescope to see it.
The star’s composition and motion don’t match that of the stars that are native to the Milky Way — or at least to the Milky Way’s bright disk. Kapteyn’s Star has a lower proportion of heavier elements — an indication that it’s extremely old. And it orbits the center of the galaxy in the opposite direction from most of the stars around it.
The combination suggests that Kapteyn’s Star came from the Milky Way’s halo, a vast region that surrounds the disk. In fact, there’s evidence that Kapteyn’s and a few other stars came from a giant cluster known as Omega Centauri.
It’s likely that the cluster is the core of a small galaxy captured by the Milky Way long ago. The stars in the galaxy’s outer precincts were pulled away — making them new residents of our home galaxy.
Script by Damond Benningfield