Black holes and the shapes of galaxies

Dynamics of galaxy cores and supermassive black holes

“…There is however a large body of work addressing the large-scale effects of central mass concentrations on triaxial spheroids or bars (e.g. Norman et al 1985, Hasan et al 1993, Dubinski 1994, Merritt & Quinlan 1998, Holley-Bockelmann et al 2002, Kalapotharakos et al 2004, Kalapotharakos & Voglis 2005, Athanassoula et al 2005. These studies generally proceed by first constructing an N-body model for the bar or triaxial spheroid, then a compact mass is inserted or grown at the center and the model is integrated forward.…”

Supermassive Black Holes in Galactic Nuclei

“…Influence of SMBHs on galactic structure. Norman, May, & Van Albada (1985) showed through N -body simulations that a massive singularity in the center of a triaxial galaxy destroys the box-like stellar orbits and hence can erase the nonaxisymmetry, at least on small scales. This has several important consequences.…”

Black holes and galaxy metamorphosis

“…Hence, the destruction of these centrophilic orbits breaks the backbone of the triaxial model and the system evolves toward axisymmetry. This effect has been shown in numerous computational and analytic studies [10][11][12][13][14][15]. In fact, the main controversies are whether the galaxy becomes axisymmetric locally or globally, and whether the transformation occurs in a few crossing times or over many Hubble times.…”

“…In particular, there are a rich variety of regular box and boxlet orbits that are centrophilic and comprise the backbone of the galaxy (Figure 1). These centrophilic orbits can be driven chaotic with the introduction of a supermassive black hole [10][11][12][13][14][15]. And, since chaotic orbits will eventually fill all available phase space, the time-averaged shape of a chaotic orbit is spherical.…”

“…However, most self-consistent N-body simulations which have studied this effect have employed astrophysically unrealistic galaxy models [10,13]. For example, the models have been highly flattened, maximally triaxial models, while observations indicate that ellipticals are most likely mildly triaxial and not very flattened.…”