COALA science: black hole physics

Geoff Bicknell, Alexander Wagner

We are engaged in the following computationally intensive projects related to black holes and other energetic astrophysical phenomena.

Feedback from Active Galactic Nuclei (AGN)

Accretion disks

The simulation of a magnetised accretion disk involves the dynamics of turbulent magnetic fields, and radiation, which cools the disk, ensuring that disks do not become too thick as a result of dissipation. Geoffrey Bicknell and Raquel Salmeron (RSAA), together with Zdenka Kuncic and Paul Dobbie (University of Sydney), are developing simulation code based on the publicly available parallelised, FLASH code from the University of Chicago in order to study magnetic dissipation and radiative effects in detail. We envisage that we will determine the way in which gravitational energy is channeled into the high temperature coronae of black hole accretion disks and into relativistic jets and winds. This follows on from various analytical papers beginning with the fundamental paper (Kuncic & Bicknell, 2004).

Dissipation in relativistic jets.

The goal of a separate but related project is to understand the manner in which relativistic jets dissipate energy near black holes thereby producing high energy radiation in the form of X-rays and gamma-rays. Geoffrey Bicknell and Alexander Wagner (University of Heidelberg) are developing robust models for the estimation of magnetic fields and particle energy densities in these dissipative regions with a view to relating them to estimates of the same parameters in accretion disks. Our approach is to carry out simulations of turbulent relativistic jet flow and to investigate the formation of shocked regions in the flow which are the source of the high energy electrons for the X-ray and gamma-ray radiation.

Feedback from black holes and starbursts

Winds, jets or radiation from black holes can prevent accretion onto a forming galaxy once the black hole is large enough, thereby affecting the evolution of the galaxy. A related area of research is that of starburst-driven winds from galaxies. Bicknell and Sutherland, and their postdocs ad students, supported by income from two Australian Research Council grants have been modelling the feedback on forming galaxies and are continuing this research in the direction of assessing the effect of outflows on forming galaxies with more spherical distributions of matter and on "cooling flow" galaxies. Their 3D simulations are computationally intensive and a sample simulation is shown in Figure 3.1. At a recent international meeting on the subject of black hole feedback, the papers published by the RSAA group were regarded as "seminal" and as an example of how to conduct simulations in this area of research.

Supersonic jet and disk simulation

Figure 3.1 - mid-plane section of a supersonic jet breaking through an inhomogeneous disk of dense gas in the core region of a radio galaxy (Sutherland & Bicknell). This 512^3 simulation was done on the APAC AC supercomputer.

 

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