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Colloquia
Statistical mechanics of gravity and gravitational-wave emission by binary black hole mergers inside stellar clusters
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Europe/Athens
Description
Dense stellar clusters are a natural environment for black holes to be born, form binaries and merge, because of the high density that enhances close encounters. Being the remnants of the death of very massive stars, stellar black holes are generated early in the life of the cluster, when primordial gas is still present. Due to mass segregation the black holes accumulate close to the center of the cluster, where gas density is high. In this dense gaseous environment, they may accrete gas and grow in mass before the gas is depleted because of stellar formation feedback processes. In addition, the accretion hardens the binary and accelerates mass segregation in the center. I suggest that this process results in such an increase of BH masses that the upper black hole mass gap of 50-130 solar masses, suggested by supernova theory, is populated. This will enhance binary black hole mergers and induce a characteristic spin signature detectable by LIGO. I further suggest that a phenomenon of gravitational osmosis takes place in two-component astrophysical systems. Due to this effect, dense stellar clusters can host hundreds of black holes (solute) stabilized by the gravitational fluctuations generated by stars (solvent) flybys. These black hole subclusters will host binary black holes that will provide additional heat energy to the core of the cluster by close encounters contributing to the stabilization of the cluster. I will finally consider systems with regular orbits, such as black holes orbiting a supermassive black hole in galactic nuclei. Like the spins in a ferromagnet the angular momenta of the orbits present order-disorder phase transitions. In the ordered phase, angular momenta are aligned resulting in the formation of a black hole disk, where binary black hole mergers are more frequent.
Videoconference via https://us02web.zoom.us/j/84400858137
