Star ClustersStar Clusters

Pre clustersPre clusters

Courtesy University of Oregon

TypesTypes

AssociationsAssociations Ironically, a Ironically, a disdisassociating associating

open clusteropen cluster Big Dipper/Ursa MajorBig Dipper/Ursa Major

Open ClustersOpen Clusters ~1000 stars~1000 stars Found in the spiral arms of the Found in the spiral arms of the

galaxygalaxy Mostly young hot starsMostly young hot stars

Pop IPop I

Globular ClustersGlobular Clusters ~1 million stars~1 million stars Found in the galactic haloFound in the galactic halo Mostly old starsMostly old stars

Pop IIPop II

Double ClusterDouble Cluster

What stellar ages tell us:What stellar ages tell us:The Turnoff PointThe Turnoff Point

We can know We can know something about the something about the age of a cluster of age of a cluster of stars by looking at stars by looking at when the most when the most massive stars turnoff massive stars turnoff the MSthe MS

Two animations followTwo animations follow

9.210 )(10 sunM

Mt

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

Beehive Open ClusterBeehive Open Cluster

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

IR image of the Arches ClusterIR image of the Arches Cluster

About 33 pc from the About 33 pc from the galactic nucleusgalactic nucleus

100 O class stars100 O class stars Globular or Open??Globular or Open??

Most densely packed Most densely packed cluster observedcluster observed

Separation ~ light Separation ~ light weeks weeks apartapart

Not these arches ->