Tähtikokoelmia

Tähtikokoelmia is a Finnish term that translates to "star collections" in English. In astronomy, it refers to a collection of stars that are gravitationally bound together and often share a common origin. These collections can vary significantly in size and structure, ranging from small groups of a few dozen stars to vast assemblages containing millions or even billions of stars.

The most well-known types of tähtikokoelmia are star clusters. These are broadly categorized into two main groups: open clusters and globular clusters. Open clusters, like the Pleiades, are typically younger, loosely bound collections of hundreds or thousands of stars found in the disk of galaxies. Globular clusters, on the other hand, are much older, denser, and spherical collections of hundreds of thousands to millions of stars, usually found in the halo of galaxies.

Beyond these primary classifications, the term tähtikokoelmia can also encompass other celestial groupings. Associations are very loose and temporary groupings of stars, often with similar velocities but without strong gravitational ties. Stellar streams are also considered a form of tähtikokoelmia, representing remnants of tidally disrupted star clusters or dwarf galaxies that are spread out in a stream-like formation within a larger galaxy. Studying these collections helps astronomers understand stellar evolution, galaxy formation, and the dynamics of the universe.