Abstract
The galactic population of globular clusters are old, dense star systems, with a typical cluster containing 104–107 stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss the theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution which lead to relativistic binaries, and current and possible future observational evidence for this population. Globular cluster evolution will focus on the properties that boost the production of hard binary systems and on the tidal interactions of the galaxy with the cluster, which tend to alter the structure of the globular cluster with time. The interaction of the components of hard binary systems alters the evolution of both bodies and can lead to exotic objects. Direct N-body integrations and Fokker-Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.
Highlights
Relativistic binaries containing white dwarfs (WDs), neutron stars (NSs), and black holes (BHs) in compact orbits are over-represented in globular clusters compared with their population in the galactic field
Considering that the time for a close passage of two neutron stars is on the order of milliseconds and that the age of a globular cluster is 1010 yr ∼ 1020 ms, we find that the time scales span 20 orders of magnitude
Noting that each encounter increases the binding energy by about 20% and that roughly 1/3 of this energy goes into binary recoil, the minimum binding energy Eb min of an ejected black hole binary is where M is the average mass of a globular cluster star and W0 = M |φ0|/kT is the dimensionless central potential
Summary
Added 16 new references and latest observations. Page 5: Added “and possible black holes”. Page 5: Added explicit references to sections. Page 14: Added sentence and references to Richer (2008) and Strickler (2007). Page 14: Added reference to Dieball (2007). Page 14: Added last two sentences and references to Ivanova (2008) and Freire (2008). Page 14: Added ω Centauri and reference to Noyola (2008). Page 14: Added two sentences and references to Bash (2008) to reflect latest observations of black holes. Page 14: Added sentence and reference to McLaughlin (2006). Page 15: Added new observations in M54, NGC 288, M30, and NGC 2808. Page 17: Changed reference of table from Camilo and Rasio (2006) to Freire. Page 18: Added new entries to reflect current observations. Page 38: Added last sentence and reference to Willems (2007)
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