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Interesting behaviour in and on the sun is nearly always associated with magnetic activity. Paul Cally , together with postdoc Alina Donea and students Ashley Crouch (PhD recently completed), Hannah Schunker, and John McCloughan, applies the theory of Magnetohydrodynamics to discover how the sun's matter interacts with its magnetic fields. Particular interests include (i) how the sun's oscillations are affected by magnetic fields in sunspots, and how this can be used to probe their interiors (Crouch, Schunker); and (ii) how instabilities at the base of the solar convection zone can develop, with profound consequences for the sun's overall magnetic behaviour (McCloughan).
Hannah Schunker and Paul Cally are undertaking an observational study of the absorption of p-modes in sunspots using the technique of helioseismic holography. The aim is to verify Ashley Crouch's results concerning optimal absorption at magnetic field inclination of 30 degrees, and to correlate phase changes and the direction of surface velocity with the ingression field of the p-modes.
Helioseismic (acoustic) holography is used to detect acoustic sources that produced solar quakes. It has been used to detect enhanced acoustic emission from three major ``sun quakes'' , to model the influence of the active region magnetic fields on acoustic signals, to image the far side of the Sun, which allows us to detect farside active regions and to study the statistical character of acoustic excitation.
Helioseismic holography has also been used to image active regions on the far surface of the Sun (the side facing away from the Earth). We can predict the appearance of solar active regions up to a week or more before they rotate around to the front side. This has important implications for space weather forecasting. However, there are a lot of things that we do not understand...
John McCloughan's PhD project will be looking at instabilities in the Solar Tachocline. The tachocline is a shear layer at the base of the solar convection zone. He and Paul Cally will be attempting to develop a three-dimensional non-linear model of the solar tachocline which incoporates magnetohydrodynamical instabilities.
Nucleosynthesis is the study of how the elements in the Universe came into being. The Big Bang produced Hydrogen and Helium, but everything else has been made in stars. Some elements are made in supernova explosions, when stars die. These elements include gold and iron, for example. Some elements are made in red-giants, such as most of the carbon in your body and the fluorine in your toothpaste! At C.S.P.A. we have a group of students and researchers (S.I.N.S) working on these questions, including Dr John Lattanzio and PhD students Simon Campbell and Carolyn Doherty.
Stars are the basic building blocks of astronomy, and how they change as they age is known as "stellar evolution". C.S.P.A. astrophysicist Dr John Lattanzio studies stars of various masses, trying to determine how their interiors change as they go through the various burning phases from Hydrogen burning on the main sequence, through to the instabilities known as "Helium Shell Flashes" when the burning shell will release 100 million times the Suns energy output, but for only a few days. Many people at CSPA work in this area, or the closely related areas of nucleosynthesis and abundance analysis.
When the Universe was young it was composed entirely of H and He. The stars which formed then were very different to the stars that are around today. The lack of heavier elements alters the way they behave. The unusual compositions seen in the most metal-poor stars, discovered recently with large telescopes, require an understanding of the very earliest stars, their evolution and nucleosynthesis. This is currently being studied by Dr John Lattanzio and PhD student Simon Campbell.
Stars usually appear in clusters, and the largest are the magnificent globular clusters, containing up to a million stars. These clusters show some very strange compositions. For example, the amount of iron in each star is the same, to high accuracy, within each star in a given cluster. But the amount of Oxygen or Carbon can vary by a factor of 10 or more! What causes this? Is it something within the star? Something peculiar about the history of the cluster? By combining theoretical calculations and observations, CSPA astrophysicists Dr John Lattanzio, Dr Allie Ford and students Lisa Elliott, Simon Campbell and Amanda Karakas are trying to answer these and related questions.
Most people have heard of "red giants", but astronomers have many different names for different kinds of red-giants. One of the most interesting are the AGB or "Asymptotic Giant Branch" stars. These stars are nearing the end of their lives, and will soon die as a planetary nebula surrounding a white dwarf. But during the last million years of their existence they develop a recurring instability in their nuclear helium burning shell, and flare up to produce 100 million times the energy output of the Sun. This last for just a few days, and then it decreases back to normal. Then, a few thousand years later, it happens again. This has profound effects on the evolution and nucleosynthesis occurring in these stars, and is studied by many people at CSPA, including Dr John Lattanzio and PhD students Amanda Karakas, Simon Campbell and Lisa Elliott.
Planets are large bodies which orbit stars. We have developed an understanding of how they move through space by observing nearby objects such as Mars and Jupiter. Learning more about out local planets can provide us with information about how the solar system formed, and the potential for life on other worlds. Kepler's laws of dynamics were discovered from observations of how the planets moved through the sky. Recent interest has been sparked by the discovery of more than one hundred planets orbiting distant stars.
Einstein's theory of General Relativity is the language which ties together gravitation, mass, energy and the geometry of space-time. It gives us the means to probe the inherent structure of neutron stars, pulsars, and the shape and fate of our Universe. It also allows us to describe the powerful gravitational fields which are generated by cataclysmic events such as the collision of black holes and the deaths of supermassive stars. General Relativity predicts that these events will radiate gravitational waves and with detectors nearing sufficient sensitivity, the world G.R. community is poised on the edge of a new era of gravitational astronomy. The MONash General RELativistS (MON.G.RELS) are involved in studying a broad range of relativistic phenomena.
In order to understand and model a vast number of general relativistic events, it is imperative that we are able to produce accurate and stable numerical models of things like black holes and other compact objects. At C.S.P.A. we have a couple of different approaches to this. Dr. Leo Brewin is involved in applying finite element lattice methods to general relatistic modelling. Dr. Tony Lun and Elizabeth Stark are currently researching the stability of the Einstein equations in their numerical form by testing out modified forms of the equations.
Smoothed Particle Hydrodynamics was developed independently in 1977 by L.Lucy (Cambridge), and Joe Monaghan here at Monash. It is a computational method for calculating complex gas flows by, rather than laying a grid over the gas region and caculating flows across it, replacing the fluid with discrete particles. By changing the emphasis from flows across grid structures and surfaces to interactions between two particles, SPH has the ability to model an incredibly diverse range of problems. These include fracturing solids, elastic collisions through to more conventional fluid models such as viscous lava flows and breaking waves.
The computational particle method of SPH was extended recently, by Joe Monaghan and Stuart Muir, to be able to perform calculations for relativistic gas flows. This opens the door for many exciting studies of both high velocity fluids (relativistic Heavy Ion Collision Studies and relativistic Jet Outflows) through to studies of gas dynamics in the vicinity of a black hole (accretion studies).
Turbulence is the seemingly random behavior of a fluid which occurs all over nature, in the atmosphere, the oceans, the interior of stars and within internal combustion engines. Hence, being able to accurately compute turbulence has a huge range of applications. While the basic equations that describe turbulence are well known and relatively simple, their solutions are incredibly complex and the computing power needed to find them transcends any imaginable computer. By using a simple extension of SPH known as the SPH alpha turbulence model, we attempt to model some aspects of the turbulent flow, as opposed to direct calculating them or ignoring them. This allows for accurate simulations of turbulent flow which neither discard import flow dynamics, nor become unmanageably expensive to compute.
The SPH particle method is currently being used by Joe Monaghan and Johnny Hitti to model pyroclastic flows. Pyroclastic flows are the outflow of many violent volcanic eruptions and are a very hot multiphase mixture of gases, ash and rocks which sometime flow into waters. Their behaviour is very similar to that of a particle-laden gravity current. The particle nature of SPH allows us to represent each phase, and each component of phase, with separate fluid particles each with a variable resolution in both space and time.
Maser emission from molecules in the gas allows radioastronomers to pinpoint the sites of newly formed high-mass stars, which are shielded from optical telescopes by the enveloping cloud of dust and gas. Dr. Peter Godfrey and Dr. Dinah Cragg are involved in modelling these masers with the aim of better understanding the star-forming environment.
Dr. Peter Godfrey provides laboratory support for radioastronomy by accurately measuring the transition frequencies of known and potential new interstellar molecules. This work is carried out in the School of Chemistry microwave spectroscopy laboratory.
Bipolar outflows are ubiquitous amongst young stellar objects (YSOs), where 200 km/s, often symmetrical, jet flows are observed to arise from the centres of such objects. There is general consensus that the flows arise from the disks that surround YSOs and that they are magnetically driven. Most models are of the "centrifugal wind type", where material is flung from the YSO by a magnetic field line. The usual analogy is that of a bead flung from a wire. This model, however, has a number of problems: slow acceleration and the inability to explain the observed dependence of the flow on Extreme UltraViolet radiation (EUV). These problems can, in part, be overcome if one considers a model where the flows are primarily driven by a magnetic field where the field lines are parallel to the disk surface. This magnetic pressure model is being developed by Dr Liffman
When one opens a primitive meteorite, it is always
found that the meteorite contains small spherical rocks
called chondrules and, possibly, other amorphous stones called calcium
aluminium inclusions. These rocks were, very probably, the first objects to
form
in the solar nebula - the disk of gas and dust that surrounded
the young Sun and from which the planets were formed. Scientists
have known about chondrules for over two hundred years, but
how they were formed still remains a mystery. About a decade ago, Dr Liffman
proposed that these objects were produced by a solar bipolar jet flow,
in the inner regions of solar nebula, and subsequently ejected to the
outer regions of the nebula where they agglomerated with dust particles
to form the meteorites we see today. This theory has become, at least
amongst astrophysicists, the most popular theory of chondrule/CAI formation.
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