I assumed that John meant a single asymmetrical located black hole orbiting near the end of the bar structure.Chris Peterson wrote: ↑Sat Aug 29, 2020 2:20 pm
It's not even clear why a pair of black holes in the center of a galaxy would produce an asymmetric structure of stars. The mass of the stars in a galaxy's core hugely outmasses one or two black holes. And the black holes would be orbiting each other, so they wouldn't be maintaining a fixed orientation that you'd probably need to form any structure in the first place. I'd expect the core of a galaxy that contained two black holes to have the same structure that the core of any unbarred galaxy has- spherical.
What the sensitivity of spiral structure density waves might be to such a strategically place black hole is unclear. (Some globular clusters are as massive as the Milky Way's central black hole but are not strategically located such that they would affect spiral structure density waves.)
However, I find it hard to believe that such an asymmetrical located black hole would go unnoticed in our own galaxy.
https://en.wikipedia.org/wiki/Spiral_galaxy wrote:<<The first acceptable theory for the spiral structure was devised by C. C. Lin and Frank Shu in 1964, attempting to explain the large-scale structure of spirals in terms of a small-amplitude wave propagating with fixed angular velocity, that revolves around the galaxy at a speed different from that of the galaxy's gas and stars. They suggested that the spiral arms were manifestations of spiral density waves – they assumed that the stars travel in slightly elliptical orbits, and that the orientations of their orbits is correlated i.e. the ellipses vary in their orientation (one to another) in a smooth way with increasing distance from the galactic center. This is illustrated in the diagram to the right. It is clear that the elliptical orbits come close together in certain areas to give the effect of arms. Stars therefore do not remain forever in the position that we now see them in, but pass through the arms as they travel in their orbits.
The density wave theory also explains a number of other observations that have been made about spiral galaxies. For example, "the ordering of H I clouds and dust bands on the inner edges of spiral arms, the existence of young, massive stars and H II regions throughout the arms, and an abundance of old, red stars in the remainder of the disk". When clouds of gas and dust enter into a density wave and are compressed, the rate of star formation increases as some clouds meet the Jeans criterion, and collapse to form new stars. Since star formation does not happen immediately, the stars are slightly behind the density waves. The hot OB stars that are created ionize the gas of the interstellar medium, and form H II regions. These stars have relatively short lifetimes, however, and expire before fully leaving the density wave. The smaller, redder stars do leave the wave, and become distributed throughout the galactic disk.>>