Demographics of Multi-Messenger Supermassive Black-Hole Binaries from the Illustris Cosmological Simulation (DSI-SRP)
This DSI-SRP fellowship funded Katharine (Katie) Cella to work in the laboratory of Professor Stephen Taylor in the Department of Physics and Astronomy during the summer of 2021. Katie is a senior with majors in Computer Science and Physics and a minors in Mathematics.
The project funded by this fellowship aimed to determine the properties of binary black hole systems that are most likely to be detected using multi-messenger astronomy, in other words detected by both their electromagnetic and gravitational wave radiation. Specifically, the project is focused on supermassive black hole binary systems that are detectable by the pulsar timing array and produce a variable electromagnetic signature due to the doppler shifting of the light from the gas surrounding the smaller of the two black holes. Doppler shifting is a relativistic effect caused by the large and changing observable velocity of the smaller black hole. Current observational astronomy does not yet have the sensitivity to detect this regime of gravitational waves, but is expected to soon. Thus, the data comes from the large hydrodynamical simulation, Illustris. Illustris simulates a cubic volume with a side length of 100 Mpc, which is much smaller than the size of the universe, and thus requires the use of a Gaussian Mixture Model to resample the simulated systems and multiple Monte Carlo draws to create appropriately sized realizations of the universe. Preliminary results show that over 100 realizations there is an average of less than 5 systems that were detectable in both gravitational waves and electromagnetic radiation, and an average of less than 1 with gravitational wave detection probability above 10%. Using the flux limit of the Legacy Survey of Space & Time (LSST) of the Vera Rubin Observatory the gravitational wave detectability was the limiting factor in the number of observable systems. Katie plans to continue to expand her work in her senior year to confirm results, include more models for electromagnetic detection, modify the models to account for eccentricity in the binary systems (right now they are all assumed to be circular), and to publish her work in a scientific research paper.
In addition to receiving support through a DSI-SRP fellowship, this project was supported and facilitated by the DSI Data Science Team through their regular summer workshops and demo sessions.