1. Globular Clusters: HST Breathes New Life into Old Fossils STScI Public Lecture Series Jay Anderson August 3, 2010

2. Plan for the Talk Overview of Globular Clusters (GCs) Omega Cen and IMAX Stellar populations GCs Black holes in GCs?

3. Globular Clusters “Textbook” simple stellar populations –Formed stars early –Single cloud, single metallicity, single age –Not large enough to self-enrich –Continue orbiting in spheroid of Galaxy Perfect laboratories to study stellar evolution

4. OMEGA CEN EARLY-RELEASE IMAGE History of this image 1) Why taken? 2) Why ERO? 3) Why “saturated” ?

5. Familiar digital cameras: three at once Hubble: one Filter at a time James Webb ST: two at a time!

6. 10x10 Early Release Field Central Field

7. The central field… Blue Red

8. HUBBLE IMAX: MAYA was used to render the scene in 3-D 8

9. Decomposing the image… “a point source has no hair” RealSimulated close upwide view The PSF

10. What Astronomers see… 1) Main Sequence 2) SubGiant Branch 3) Red Giant Branch 4) Horizontal Branch 5) White Dwarf Sequence

11. Easy to identify stars… RGB WDs SGB HB MSTO Red Dwarfs BSs

12. More metals More Helium Age Red Giant Branch A B C Globular clusters have traditionally been defined as textbook “simple” stellar populations: bound clusters of stars at the same distance, with the same age, and the same metallicity.  same small cloud Stellar Populations “Isochrone” all at the same age

13. Omega N6397 47T Omega CenNGC639747 Tuc Extra sequences

14. Omega Centauri: Globular Cluster or Dwarf Spheroidal? Cambridge, UK 2001 ME!

15. Stellar Populations More metals More Helium Age Inversion! More metals metal poor intermediate metal rich Red Giant Branch Similar to galaxies… More metals

16. Is Omega Cen a GC? Could the textbook globular cluster not even be one? 47Tuc N2808 N6656 N6388 OmCen ®

17. Are there any “globular clusters”? Questions to answer: 1)How do clusters enrich themselves? 2)Why are they all so different? 3)Is it all clusters, or just heavy ones? 4)What connection is there between clusters and galaxies? 5) Any relevance for star formation we see going on today? Is Omega Cen a globular? NGC2808 NGC6652

18. HST is a GC machine… HST’s advantages 1)Resolution: separate stars 2)Lower background: concentrate star, not sky 3)Stability: no atmosphere, same PSF 4)UV and IR coverage Cluster topics: 1) Cluster-field separation 2) Search for black holes

19. The first full CMD ever Richer et al. 2005 observed NGC6397 with 126 orbits –Discoveries End of WD cooling seq Blue hook at bottom! End of MS? –Limitations: field stars Blue Faint Bright Red

20. Proper-Motion Cleaning PI-Rich, UCLA

21. CLUSTER IN A CLUSTER

22. Intermediate-Mass Black Holes (IMBHs) in GCs BHs known to exist with –~10 M SUN : HMXBs –~10 6 M SUN : SMBHs at galaxy centers High-Mass X-ray Binaries Super-Massive Black Holes

23. Ghez Group at UCLA See: http://www.astro.ucla.edu/~ghezgroup/gc/pictures/orbitsMovie.shtml

24. Intermediate-Mass Black Holes (IMBHs) in GCs BHs known to exist with –~10 M SUN : HMXBs –~10 6 M SUN : SMBHs at galaxy centers why not? –~10 4 M SUN : IMBHs Could explain a lot! 10,000 M SUN ~20 km/s Greene & Ho (2006) Higher Velocities  Bigger Black Hole  High-Mass X-ray Binaries Super-Massive Black Holes

25. IMBHs in Globular Clusters Several ways to find (PMs or RVs) –Fast moving star in orbit (smoking gun) –Rise in velocities at center –Also ways without PMs or RVs… Pulsars, accretion signatures –Indirect: cusps Several ways to not find –Not enough stars/gas to sample its environs –Nearby stars all dark, ejecting binaries Easiest places to look: –Clusters with cusps & slow velocities Zone of influence r BH ~ M BH /  2 Omega Cen is not the easiest place to look… yet…

26. Detections/limits in the literature –M15: back and forth; currently not required… –NGC6752: negative P pulsars: 1000 M SUN –47 Tuc: upper limit of 1500 M SUN –G1 in M31? X/Radio emission and velocities  Cen: circumstantial evidence: –IFU from ground saw fast stars at center 40,000 M SUN IMBH? HST should see this… Previous Observations…

27. Omega Cen: a Ground-Based Image (Lehman)

28. HST-vs-Ground

29. Measuring Proper Motions Epoch1: 2002Epoch2: 2006

30. Stars with good measured motions 3  Zone of Influence

31. PM Profile Total motions of the 1000 stars in the inner 10  100 stars/bin Proper Motions indicate no obvious mass at the center. Certainly not 40,000 M SUN ; at most 12,000 M SUN

32. Simulation on Following Page: One frame = 100 years Total time = 1000 years

33. Moving stars 12765349108

34. AT OUR SPEED…

35. With a BH… See: http://www.stsci.edu/~jayander/omcen_sim_pms_2d_wbh.mpg

36. Future Directions… Omega Cen –More time? More stars? Better models? Other clusters coming! NGC 362 M15 NGC 6624 NGC 7099 NGC 6681 AND MORE!