Coagulation

In dense environments, compact binaries can repeatedly coalesce. Like blobs in a lava lamp, the compact binaries coagulate into large and larger objects. The details, however, depend on the interacting environment that forces the bodies together; different environments like AGN disks or globular clusters have very different physics. In a new study led by Z. Doctor and RIT student D. Wysocki, we describe a generic framework to BH coagulation. We show how BH masses and spins grow with time, for different interaction choices. And we explain how to constrain these parameters, and the natal BH population, via comparison with observations.

For experts:Why should you care? Hierarchical BH-BH formation scenarios make strong predictions connecting the mass and spin distributions at different mass scales. Our framework shows how to stringently constrain these models via GW observations, allowing for arbitrary complexity in the natal BH distribution. We explore realistic BH natal mass and spin distributions, allow for physical recoil kicks from a realistic confining potential, and show how to constrain our physically-parameterized phenomenological model via comparison to GW observations.

For more information:

• Doctor et al, Black Hole Coagulation: Modeling Hierarchical Mergers in Black Hole Populations (arxiv:1911.04424), submitted to ApJ

• Closely related: our group’s recent work on AGN disks (McKernan et al 2019; Yang et al PRL 2019) describes a new mechanism by which BH can form hierarchically.

PopModels and the BBH merger rate: Daniel Wysocki’s population code PopModels is one of the methods used to compare gravitational wave observations to different candidate populations of binary black holes. This is the first code which can handle generic generative models (i.e., the output of Monte Carlo procedures to produce synthetic binaries, a typical method that theorists use to characterize their formation scenarios).