It is estimated that there are over 1’100 open clusters in the Milky Way only. They are usually made of a few thousands stars of the same age that were formed from the same giant molecular cloud. They are bound by mutual gravitation influence but may be disrupted by close encounters with other clusters or clouds of gas.
The Pleiades/Seven sisters (M45)
Open star cluster (M35)
Pinwheel star cluster (M36)
Open star cluster (M37)