Observational Evidence for Black Holes in Globular Clusters

Karl Gebhardt (UT Austin)

Results to Date from Dynamical Studies

• M15 has been painful for many years

Gerssen et al. 2003 claim a 2000 Msun BH from radial vels

Baumgardt et al. 2003 say no evidence

McNamara et al. 2003 say no evidence from proper motions

• G1

Gebhardt, Rich, & Ho claim 2e4 Msun BH

Baumgardt et al. 2003 say no evidence

New data being analyzed

• NGC 6752

Drukkier et al. 2003 claim large M/L increase from pm’s

Xie et al. 2003 claim little M/L increase from radial vels

Colpi et al. 2003 use pulsars to argue for something massive

Current BH/sigma correlation using published results

Comparing M15 radial velocities with proper motions (McNamara et al), using distance as

measured from Kraft and Ivans 2003 (11.2 kpc)

Comparison with Baumgardt et al dispersion profile, including a BH of 1700 Msun.

Models with adding a BH to Baumgardt profilefor the 100% and 0% ns population

G1 with WFPC G1 with HRC

NGC6752 Pulsar Strangeness

Rotation in Galactic clusters

Central Rotation in Galactic clusters

Central Surface Brightness Profiles

BH/sigma correlation using isotropic models

Conclusions

• M15 and G1 still have black holes as the best fitting model

• central light profiles for clusters show a range of slopes

• rotation in clusters is important to consider

• many clusters show a statistically significant increase in the central rotation, which has a PA that is not correlated with that of the main body rotation