WoU-MMA: Tuning In to the Echoes of Black Hole Seeds

The lives of galaxies and their central super-massive black holes (SMBH) are inextricably intertwined, and have evolved together over cosmic time. Intermediate-mass black holes (IMBH; 100 – 1-million solar masses) are presumably the “seeds” of the SMBH, though the mechanism(s) connecting the former to the latter are poorly understood and very difficult to observe using electromagnetic radiation.

This research program will use computer simulations to model three distinct IMBH formation mechanisms in order to predict the redshifts, masses and rates of IMBH mergers. These gravitational wave signatures will be detectable with the next generation of gravitational wave telescopes like ESA/NASA’s Laser Interferometer Space Antenna (LISA). The principal investigator will also increase the recruitment and retention of students from under-served communities in STEM fields through a new community college research and mentoring program.

The primary objective of this research is the prediction of gravitational wave signals of IMBH mergers from the early universe to the current epoch. To accomplish this objective state-of-the-art cosmological hydrodynamical simulations will be used to study their formation and evolution in the early universe. The primary data will consist of a large sample of high-resolution simulated galaxies that incorporate a full suite of black hole physics.

These simulations will consider three different IMBH formation mechanisms: the collapse of individual massive Population III stars, clusters of stars, and entire molecular cloud complexes, and will additionally include the effects of gravitational recoil in a self-consistent manner for the first time. The principal investigator will then deduce the rates, masses, and mass ratios of black hole mergers in each simulation, track the overall growth of IMBHs into SMBHs within their host galaxies, and calculate the contribution of each type of IMBH to the gravitational wave signal observable by LISA.

These merger events are unlikely to emit any light, and thus their discovery will be an extraordinary view into the formation and growth of SMBHs. The contribution of IMBHs to the gravitational wave signal has not been modeled in detail because there are so many unanswered questions about their formation and evolution. The proposed research will be foundational to making theoretical predictions involving early IMBH formation in the context of galaxy evolution and for correctly interpreting LISA detections. This project thus advances the goals of the NSF Windows on the Universe Big Idea.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.