The Astrophysical Fluid Dynamics group studies the processes involved in star and planet formation. We run global simulations of these systems, solving the equations of hydrodynamics during gravitational collapse to study how these objects are formed. The primary numerical method we utilise is Smoothed Particle Hydrodynamics (SPH), originally developed by Joe Monaghan.
We are always on the lookout for interested and motivated students to join us in pursuing research towards a PhD or as part of their honours year (contact either Daniel Price or Joe Monaghan if you are interested). The group often hosts long term visitors interested in applying SPH to their own problems in wide range of research fields, and we have access to a range of national, state-level and university-level supercomputing facilities that we utilise regularly.
- Dr. Daniel Price (Monash Fellow)
- Prof. Joe Monaghan (Research Staff)
- Dr. Christoph Federrath (ARC Fellow)
- Dr. James Wurster (Postdoctoral Researcher)
- Dr. Alireza Valizadeh (Postdoctoral Researcher)
- Terrence Tricco (PhD Student)
- Hauke Worpel (PhD Student)
- Rebecca Nealon (Honours Student)
Researchers: Daniel Price, Joe Monaghan, Alireza Valizadeh, Terrence Tricco
Our group is one of the leading centres in the world developing the SPH method, a numerical method for simulating hydrodynamic fluid flow which is widely used in astrophysics. We have pioneered methods for simulating magnetic field and dust physics with SPH, but are also considered with other fundamentals such as interpolation methods. We have performed comparison studies of SPH and grid based methods, which highlight the differing strengths or agreements between these methods.
Researchers: Daniel Price, Christoph Federrath, James Wurster, Terrence Tricco
The formation of stars is one of the most fundamental processes in the universe without which galaxies and indeed, ourselves would not exist. However our theoretical understanding of star formation is relatively poor, primarily because of the difficulty in modelling the physical process which involves gravity, highly turbulent gas dynamics (at supersonic velocities), magnetic fields, radiation, molecular and dust chemistry. Star formation also involves a truly enormous range in length and time scales which makes simulating the process difficult even with the fastest computers. One of the key aspects of our work here at Monash is to understand the role of magnetic fields in the star formation process, using simulations that form whole star clusters rather than just isolated stars, which gives a much deeper, statistical, picture of star formation that can be compared to real molecular clouds. Much of this work involves developing accurate numerical algorithms for simulating self-gravitating radiation-magnetohydrodynamics over the wide range of length and time scales involved in star formation (which we achieve using the Smoothed Particle Hydrodynamics method). The simulation methods thus developed are readily applicable to other areas of astronomy (and also to many earth-bound problems for which SPH is increasingly being used), amongst which we have or are working on application to the merger of binary neutron star systems; to the nature and statistics of turbulence in molecular clouds; to the role of magnetic fields in galaxies and to warp propagation in accretion discs.
Snapshot from a calculation of star cluster formation (see the movies)
Calculation of warp propagation in an astrophysical accretion disc.
Snapshot of stars forming along filamentary lines in Mach 10 supersonic turbulence
Researchers: Daniel Price
We study the many steps involved in forming terrestrial and gas giant planets. These processes begin with micron-sized dust grains that originate in the interstellar medium, and evolve in the gas and dust discs that form about young stars. This evolution involves the collisional growth of the dust grains, and their concentration or redistribution through gas and dust two-fluid instabilities. Once such grains agglomerate to reach metre scales, we must consider the impact of gas head winds upon their motion, and at kilometre scales we must consider the dynamics of these larger bodies, known as planetesimals, as they interact with one another. It is believed that terrestrial planets, and gas giant cores, form through the coalescence of these large icy and rocky planetesimals. For gas giants there is a subsequent phase of gas accretion during which they accrete a vast majority of their final mass.
We develop SPH algorithms with which to simulate planet formation. Using complex numerical simulations, we treat many of the physical processes mentioned above, and are striving to couple the various processes together to give a more complete picture of planet formation. With these we must include the relevant physics, such as the transport of energy by radiation, the gravitational pull of the gas and dust media upon themselves, known as self-gravity, and the interactions of the solid and gaseous states of matter. Smoothed Particle Hydrodynamics (SPH) is an ideal tool for tackling these problems, allowing us to simultaneously model regions of material with huge contrasts in density and temperature, with a natural approach to modelling self-gravity, and the ability to readily trace the flow of matter. In concert with these numerical simulations, we also produce analytical models that are simpler, but can be used to pin down the essential physics involved in the different processes.
Researchers: Daniel Price, Joe Monaghan, Christoph Federrath, Alireza Valizadeh, Terrence Tricco
Leonardo da Vinci was one of the first to be fascinated by turbulent fluid flows (see his drawings of water flowing into a tank and creating vortices). Since then generations of scientists have tried to explain and to model turbulence. The most successful phenomenological model for incompressible turbulence was presented by Kolmogorov in 1941. However, turbulence in astrophysical systems such as the interstellar medium or primordial gas halos in the early Universe is highly compressible and characterized by supersonic random motions. To gain insight into this multi-scale, highly non-linear regime of compressible turbulence, we use large-scale computer simulations here at MoCA. Such simulations require massively parallelized supercomputers with thousands of processors working together in parallel to solve the gas and plasma equations governing turbulent gas flows. To enable simulations of highly compressible turbulence, learn about its statistics and role for astrophysical systems, we develop efficient parallel codes and state-of-the-art supercomputing techniques here at MoCA.
One of the most important applications of our simulations is to study the role of turbulence for the formation of stars in magnetized gas clouds. We think that the role of turbulence is threefold. First, turbulence carries sufficient energy to stabilize molecular clouds against global collapse, which would be a quick and fatal end for such clouds, thankfully not observed. Secondly, interstellar turbulence is supersonically fast, producing local gas compressions in filaments, which are the seeds for stellar birth. Finally, turbulence is the only process capable of amplifying a magnetic field exponentially fast. This process is called 'turbulent dynamo', and indeed it acts like a dynamo, efficiently converting turbulent energy into magnetic energy on extremely short timescales. Thus even the first stars that formed in our Universe probably did so in a highly magnetized plasma, a possibility often ignored. Here at MoCA we aim to understand fundamental properties of turbulent dynamo amplification and its role for star formation in the present-day and early Universe.
Drawing by Leonardo Da Vinci of pouring water creating turbulent flow
Snapshot from a calculation of supersonic turbulence in star forming molecular clouds
Comparison of turbulence driven by solenoidal and compressive forcings