What is Chaos and What Does it Have to do With Black Hole Mergers?

Abstract: In this talk, we briefly review the concept of chaos in gravitationally bound systems of interacting particles. These concepts are then applied to the classic three- and four-body problems in Newtonian gravity. A statistical mechanics methodology is applied in order to derive analytic expressions for the properties of the outcomes of these interactions. This includes the orbital parameter distributions expected for populations of binary and triple star systems produced as a result of three- and four-body interactions. Such small- number collisional interactions occur regularly in star clusters throughout the Universe, across all mass scales. At higher cluster masses, such as globular and nuclear star clusters, stellar-mass black holes (BHs) are thought to be regular participants in these interactions. This is a key step that influences directly the interpretation of observations of BH-BH mergers using gravitational wave (GW) detectors, such as aLIGO. We discuss how the ever-growing number of observed BH-BH mergers can be used to constrain the astrophysical environments from which the detected GWs originate.

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