Princeton University Thunch Talk

Most globular clusters (GCs) show evidence for multiple stellar populations, suggesting the occurrence of two or more distinct star-formation episodes. The large fraction of second population (2P) stars observed, require a very large 2P gaseous mass to have accumulated in the cluster core to form these stars. Hence the first population of stars (1P) in the cluster core has had to become embedded in 2P gas, just prior to the formation of later populations. Here we explore the evolution of binaries in ambient 2P gaseous media of multiple-population GCs. We mostly focus on compact-object binaries and follow their evolution as they evolve from wide binaries towards short periods through interaction with ambient gas, followed by gravitational-wave (GW) dominated inspiral and merger. We show this novel GW-merger channel could provide a major contribution for the production of GW-sources. We consider various assumptions and initial conditions and calculate the resulting gas-mediated change in the population of binaries and the expected merger rates due to gas-catalyzed  GW-inspirals. For plausible conditions and assumptions, we find an expected GW merger rate observable by aLIGO of the order of up to a few tens of Gpc^-3 yr^-1. These mergers are most likely to occur during the early stages of cluster evolution, such that the expected contribution to the total GWs mergers measured in aLIGO is dominated by younger massive clusters at low redshifts, while old GCs at high redshifts may contribute to current rates for models with lower 2P gas-densities. Finally, our results suggest that the conditions and binary properties in the early stage of GCs could be critically affected by gas-interactions and may require a major revision in the current modeling of the evolution of GCs.