Star Clusters

Pre clusters Courtesy University of Oregon

Types Associations Ironically, a disassociating open cluster Ironically, a disassociating open cluster Big Dipper/Ursa Major Big Dipper/Ursa Major Open Clusters ~1000 stars ~1000 stars Found in the spiral arms of the galaxy Found in the spiral arms of the galaxy Mostly young hot stars Mostly young hot stars Pop I Globular Clusters ~1 million stars ~1 million stars Found in the galactic halo Found in the galactic halo Mostly old stars Mostly old stars Pop II

Double Cluster

What stellar ages tell us: The Turnoff Point We can know something about the age of a cluster of stars by looking at when the most massive stars turnoff the MS Two animations follow

Newly found clusters in NGC 6397 (left) 1BLY; M15 (right)

Beehive Open Cluster

M80, one of the densest of the 147 known globular star clusters in the Milky Way; 28,000 LY

IR image of the Arches Cluster About 33 pc from the galactic nucleus 100 O class stars Globular or Open?? Most densely packed cluster observed Separation ~ light weeks apart Not these arches ->