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Exploring Star Clusters: A Window to the Universe

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  1. Chapter 13: Star Clusters Stars (almost) always form in clusters globular cluster Open cluster • The stars all formed at the same time • They are all at the same distance • They formed from the same material • Only difference is their masses!

  2. h & Chi Persei – Double Cluster in Perseus

  3. Messier 35 and NGC2158 – “open clusters” of different ages

  4. Pleiades Open clusters: Contain < ~ 1000 stars Loosely gravitationally bound together Younger than globular (some still contain O and B stars) More enriched in heavy elements (“Population I” stars)

  5. Messier 50 – An “open cluster” of stars

  6. Open clusters that have become gravitationally unbound are stellar associations. If they continue to have similar proper motion, this is a moving group. Ursa Major moving group

  7. globular clusters: Contains ~1000-106 stars Extremely old: billions of years Population II (low in heavy elements)

  8. Globular cluster M2 “He who cannot see gravity at work here has no soul.” - Richard Feynman

  9. HD Diagram for star clusters: only difference is mass

  10. Isochrones: Lines of ‘constant age’ for stars of different masses

  11. M.S. LIFETIME for STAR at TURNOFF = AGE of CLUSTER

  12. Star cluster website

  13. Star clusters are useful to: Verify stellar evolution models Determine distances to nearby galaxies Determine chemical composition of universe in the very distant past

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