These movies show typical results of “zoom-in” simulations, following the gas that falls to galaxy centers in a major merger all the way down until it is accreted by a super-massive black hole. The largest-scale simulations begin with galaxy-galaxy mergers; these mergers funnel gas into the central regions of the galaxies, raising its density by a factor of ~100-1000. Because of the huge dynamic range in the problem, it is impossible to resolve the small-scale physics around the black hole at the same time as the large-scale galaxy collision. But we can “zoom in” on these central conditions (scales of ~10pc - 1kpc, or 30-3000 light-years), and re-simulate them at higher resolution. The “intermediate” scale simulations above show examples of this, given some slightly different initial conditions. The gas densities build up so high that they are vulnerable to global gravitational instabilities, forming features like bars, rings, and spirals, that channel gas to yet further radii. Continuing this re-simulation technique, we can follow gas down until it forms a nuclear disk at ~1-10pc or 3-30 light-year scales. This provides further structure that moves the gas down yet further, to a tenth of a parsec (0.1pc), where a traditional quasar accretion disk forms, carrying the material down to the supermassive black hole. This cascade of gravitational instabilities can fuel the black hole at rates of up to ~10 solar masses per year, in these runs (giving luminosities comparable to the brightest observed quasars in the Universe, up to redshifts z=6).
The movie shows the galaxy gas, followed over a series of scales from a galaxy merger down to a central super massive black hole (see description below).
Color shows the effective turbulent motions (sound speed) in the gas, from ~10 km/s (blue) to ~100 km/s (yellow)
Brightness shows the projected gas surface density, scaled logarithmically.
The simulation shows the re-simulated central (~10-1000 pc) regions of a galaxy merger, at a stage where central gas densities are high, and the system forms a clumpy spiral instability. It continues to zoom in.
The simulation shows the re-simulated central (~10-1000 pc) regions of a galaxy merger, at a stage where central gas densities are relatively low, but inflow piles up in a ring that soon collapses. It also continues to zoom in.
The simulation shows the re-simulated very nuclear regions (~0.1-50 pc), following from the above “spiral” conditions. A nuclear, lopsided disk forms that drives bright quasar activity.