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“Formation of Supermassive Black Hole Binaries in Hydrodynamical Galaxy Mergers” Dr. Stelios Kazantzidis Ohio State University |
| In recent years, compelling dynamical evidence has indicated that supermassive black holes (SMBHs) are ubiquitous in galactic nuclei. According to the currently favored cold dark matter (CDM) cosmological model, structures in the Universe grow through a complex process of continuous mergers and accretion of smaller systems. Thus, the hierarchical buildup of SMBHs by massive seed black holes present at the center of protogalaxies and the formation of SMBH binaries appear as natural consequences in any hierarchical cosmogony. Nonetheless, so far it has not been possible to show how two SMBHs bind during a hydrodynamical galaxy merger due to the difficulty of modeling a wide range of spatial scales. I present the results of the first multi-scale N-body + smoothed particle hydrodynamics simulations that track the formation of a SMBH binary down to scales of a few light years following the collision between two spiral galaxies. Strong gas inflows associated with the merger process produce non-axisymmetric, massive turbulent nuclear disks. The two SMBHs are embedded in these nuclear disks and their relative orbit shrinks owing to dynamical friction against the predominantly gaseous background. The black holes form an eccentric binary in the disk in less than a million years for an ambient gas temperature and density typical of a region undergoing a starburst. The initial conditions necessary for the eventual coalescence of the two black holes as a result of gravitational radiation emission appear to arise naturally from the merging of two equal-mass galaxies whose structure and orbits are consistent with the predictions of the CDM model. These findings have important implications for planned gravitational wave detection experiments such as LISA. |