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Two stellar-mass black holes in the globular cluster M22
Jay Strader1, Laura Chomiuk, Thomas J Maccarone
1Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA. strader@pa.msu.edu
Nature
|October 6, 2012
Summary
Two stellar-mass black holes were discovered in the M22 globular cluster, challenging ejection theories. This finding suggests globular clusters may retain more black holes than previously thought.
Area of Science:
- Astronomy
- Astrophysics
- Stellar Dynamics
Background:
- Globular clusters are predicted to eject most stellar-mass black holes due to dynamical interactions.
- The scarcity of observed black-hole/X-ray binaries in Milky Way globular clusters supports this ejection hypothesis.
- Previous black hole detections in extragalactic globular clusters lacked mass determination and could be intermediate-mass black holes.
Purpose of the Study:
- To investigate the presence and nature of compact objects within the Milky Way globular cluster M22.
- To test theoretical predictions regarding the population and dynamics of stellar-mass black holes in globular clusters.
Main Methods:
- Detection and analysis of flat-spectrum radio sources within the M22 globular cluster.
- Radio and X-ray flux ratio analysis to characterize the accreting objects.
- Comparison of observed properties with theoretical models for black holes in globular clusters.
Main Results:
- Identification of two accreting stellar-mass black holes (approximately 10-20 solar masses each) in the M22 globular cluster.
- Observation of a high radio-to-X-ray flux ratio for these black holes, consistent with larger predicted masses in cluster environments.
- Evidence suggesting black hole ejection from globular clusters is less efficient than most models predict.
Conclusions:
- The M22 globular cluster likely hosts a significant population of 5-100 stellar-mass black holes.
- The presence of these black holes may explain the large core radius of M22 through dynamical heating.
- This discovery necessitates a revision of models concerning black hole retention and dynamics within globular clusters.
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