Black Hole Demographics in the First Galaxies*

Black holes are regions in the universe with such immense gravity that nothing can escape from. Black holes range in size from stellar-mass to supermassive. Supermassive black holes have been found within the first billion years of the universe, which challenges current theories of black hole astrophysics. There have been many theories for why supermassive black holes could exist at such an early time such as the growth of stellar-mass black holes, the direct collapse of a primordial gas cloud, or the stellar collisions and dynamical instabilities in dense star clusters. We are interested in the scenario that supermassive black holes grow from stellar-mass black holes by accumulating their surrounding material in a process called accretion and by mergers of black holes. We used the computer simulation code Enzo to simulate the formation and growth of stellar-mass black holes, and analyzed the simulation using the Python toolkit yt. In our data analysis, we look at the mass growth and orbital evolution of the black holes, and from that determine if the black holes will "sink" to the galaxy center after their formation and especially after a galaxy merger. Our work will contribute to our current understanding of how stellar-mass black holes can grow into supermassive black holes in the early universe. Moreover, since black holes may merge in the early universe, our results will also constrain the relationship between gravitational wave events and early galaxy formation.