Does M15 Possess an Intermediate-Mass Black Hole in Its Core?
Abstract
We present the results of an internal proper motion analysis of the inner region of M15 using Hubble Space Telescope Wide Field Planetary Camera 2 images. The motions of 704 stars with brightnesses above that of the cluster turnoff (V<18.3) are analyzed to determine the velocity dispersion profile within about 15" of the cluster center. The average signal-to-noise ratio of these motions is about 3, and stars in the innermost radial bin have an average core distance of only 0.7". Assuming a distance to M15 of 10 kpc, we estimate that the velocity dispersion within this innermost bin is 14.5+/-2.5 km s-1 and that it slowly decreases outward, reaching a value of 9.8+/-0.8 km s-1 at R=15.6". We find that the proper-motion dispersion profile is in good agreement with the predictions of recent N-body simulations that do not require the presence of a central intermediate-mass black hole (IMBH). The agreement between the observed profile and the N-body simulations is marginally improved if one assumes that when a neutron star is created as a result of stellar evolution, it escapes from the cluster. Based on the results of this study and a review of other investigations, it is concluded that there is little direct evidence that M15 possesses an IMBH.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2003
- DOI:
- 10.1086/377341
- Bibcode:
- 2003ApJ...595..187M
- Keywords:
-
- Astrometry;
- Black Hole Physics;
- Galaxy: Globular Clusters: Individual: Messier Number: M15;
- methods: N-body simulations;
- Stellar Dynamics