Contact detailsWelcome to my home page. Here you will find links to recent papers and talks, lecture notes and exercises as well as some recent movies related to my research in computational astrophysics with students and colleagues.
Contact details
Postal address:
Prof. Geoffrey Bicknell, Research School of Astronomy & Astrophysics,
Mt Stromlo Observatory, Cotter Rd., Weston, ACT 2611, Australia
E: geoff at mso.anu.edu.au
T: +61 (0)2 6125 9088
F: +61 (0)2 6125 0233
Selected recent papers and talks
Current Research
Restarting Jets in Mpc scale radio sources (thesis work of Vicky Safouris; collaborators Ravi Subrahmanyan and Lakshmi Saripalli)
Log density snapshot from a 3D simulation of a restarting jet. In this simulation the new jet has a Mach number of 25.9 (as does the jet that is responsible for the creation of the original cocoon, which is blue in the above image). As a result of entrainment into the original cocoon, the density ratio of jet to cocoon is of order unity. You can also download the quicktime movie.
A number of large Mpc-scale radio sources exhibit inner double radio structure - interpreted as restarting jets. PKS 1545-321show in the above left hand image, derived from ATCA and VLA radio data, is an example. Vicky Safouris has been carrying out computational and interpretational work on undrestanding the properties of such jets. One of the reasons advanced in Vicky's work, for the well-collimated structure of the inner jets in sources such as PKS 1545-321 is that the restarting jets are hypersonic and that during the initial phase of the radio source significant material was entrained into the radio cocoon as a result of turbulent interaction bewteen the cocoon and the external environment. The decrease in the sound speed in the cocoon ensures that the bow shock of the jet is supersonic.
Evolution of young radio galaxies (collaborations with Ralph Sutherland, Curtis Saxton and Michael Dopita)
On quite a different scale (say about 500 pc), we have radio sources such as 4C31.05 which is an example of a Compact Symmetric Object. Galaxies such as 4C31.05 also fit into the class of Gigahertz Peak Spectrum (GPS) Sources whose spectra turn over at a frequency of about a Gigahertz. It is generally believed that these sources are less than a million years old compared to the hundred million years of "mature" radio galaxies. At RSAA we have developed the idea that these sources interact strongly with their environment (see above papers) and in a series of computational papers we have developed 2D and 3D models for such interactions.
The sequence of images below shows the synthetic radio surface brightness resulting from one of our high resolution (512x512x512) simulations of a jet interacting with a turbulent large (kpc-scale) disk. Initially the interaction of the jet with the disk leads to a pseudo-spherical phase from about 25 - 45 kyr, then a jet breakout phase (up to about 75 kyr). Subsequently, the jet breaks free of the original bubble and starts to form a classical radio source. The eastern (left) side of 4C31.05 resembles the simulation in the bubble phase from about 25-35 kyr. The Western (right) side resembles the simulation at about 70-75 kyr when the jet is about to break free of the bubble. There is indeed a disk of gas seen in HI absorption straddling 4C31.05 perpendicular to the radio axis. We ascribe the different dynamical states of the lobes of radio plasma on both sides of 4C31.05 to asymmetry in the distribution of the neutral gas.
Downloadable quicktime movies of this simulation
The original 2D simulations in this project were done by Curtis Saxton when he was working with us as an ARC research associate. The 3D work described here will appear in a paper by Sutherland & Bicknell, which will shortly be submitted to ApJ.
The computations were carried out on the Altix supercomputer operated by the Australian Partnership for Advanced Computation (APAC).
Courses
High Energy Astrophysics (3rd/4th year course)
Astrophysical Fluid Dynamics and Magnetohydrodynamics
This page maintained by Geoff Bicknell. Last updated 5 June 2007.