Our research

Solar flares

Solar flares are dynamic events in which magnetic energy is released in the solar corona. Recent work on flares includes the construction of a model for particle acceleration in flares based on inertial Alfven waves, which attempts to account for the flare `number problem' - the difficulty in reconciling the large inferred numbers of accelerated electrons in flares with the low density of the background solar plasma.

For more information contact Mike Wheatland or Don Melrose.

Discovering exoplanets

The discovery and characterization of planets in orbit around distant stars - so called exoplanets -
is now listed among the top aspirational goals for every national astronomical program worldwide.
After centuries of speculation, conjecture and outright dreaming by astronomers, exoplanets are now known to adorn thousands of stellar systems in the night sky, with many more under strong suspicion awaiting only final confirmatory data to join the club.

Despite the recent avalanche of discovery, the exoplanetary systems discovered by Astronomy's newest field have so far raised far more questions than they have answered. For all its richness, the properties of the sample of exoplanets we now have tells us far more about the limitations of the techniques we use to find them than it does about the exoplanets themselves. The patch of discovery illuminated by our present instruments particularly favors the largest planets in the closest orbits about their host stars. The extreme examples of this (and the most celebrated exoplanet discovery - of 51 Peg - that launched the field in 1995) are known as "hot Jupiters", a name which understates their inhospitable crushing gravity combined with searing radiation field from the looming host star.

In a quest whose aspirational goal is the identification of planets capable of supporting life, or even finding biosignatures themselves, hot Jupiters score low on the real-estate desirability index. Astronomers have even begun to work out the beginnings of a valuation scheme, in which the very choicest astronomical addresses lie within the so-called "Habitable Zone". Recognizing water in liquid form as the critical environmental ingredient for life on earth, exoplanets are said to be in this zone if they are able to support a similarly temperate climate. To get a more representative picture of exoplanetary populations, including greater sensitivity to those in the habitable zone, we need new techniques to illuminate the unknown areas beyond the reach of our present instruments.

Researchers at SIfA have very strong linkages with NASA's Kepler mission, the spectacularly successful spacecraft which has unveiled more planetary candidates than all competing efforts put together. Very active groups are also engaged in opening entirely new windows onto the planetary realm, including advanced projects in both the optical and the radio attempting to capture the faint signals betraying the presence of a planet against the noise and glare of their host star. Solving the puzzle of how planets are formed and where they now reside has far-reaching implications beyond astronomy, for it helps inform our place in the universe and expectations
for life on other worlds.

For more information contact Peter Tuthill, Tim Bedding or Tara Murphy.

The apparent similarity of the bright stars which adorn the night sky is deceptive: in reality our stellar neighbors exhibit a quite staggering diversity of form and structure. The mighty supergiant stars can easily outshine our sun by a factor of ten thousand: the same factor by which our sun outshines the dimmest of the red dwarfs. The life cycle of countless myriad stars makes up the galactic eco-system, leaving behind fascinating remnants such as White Dwarfs, Neutron Stars or Black Holes whose physics takes us through the looking glass into exotic realms dominated by General Relativity.

Among the most fundamental areas underpinning of the entire field of Astronomy is a quantitative understanding of the basic properties of stars. The starting point for all physical models is knowledge of characteristics such as mass, luminosity, temperature, age, chemical composition. Fortunately, in recent years, observational astronomy has developed new technologies to deliver exquisite new studies of stellar surfaces, their immediate surroundings, and even probes of their interior structure. By revolutionizing our view of the stars themselves, we are able to see the interplay between them and the galaxies that host them, the families of planets that they harbor, and the extreme physics of the weird remnants left behind after they die.

When tomorrow's textbooks on stellar physics are written, fingerprints from the new field of Asteroseismology will appear on just about every page. In a close analogy to the way in which earthquakes can be used to study geological layers deep within the earth, disturbances from convection near the surface of stars excites standing waves whose frequencies carry information about the stellar structure right down to the impossibly deep zones at the core. This information can help us study fascinating physics under the extreme conditions in stars such as mapping their internal rotational profile, and hence the transport of angular momentum as they grow old.

In addition to hosting one of the world-leading Asteroseismology groups, SIfA are also pioneers in the highly complementary technology of high resolution interferometry. Remarkably, the most powerful imaging instruments are now able to zoom in on the stellar surface itself, directly measuring its size and temperature. For some stars, rapid rotation distorts the equator which bulges out into a flattened egg, while others show exotic perturbations from close binary companions.

Using both Asteroseismology and Interferometry combined turns out to be a particularly powerful way to gain a nearly complete observationally-based physical understanding of a star, for the first time free from simplifying assumptions and model parameters derived from theory.

Phases of the stellar life cycle at birth and at death both turn out to be particularly fascinating, and are very active areas of contemporary astronomical research. Both occur enshrouded within obscuring halos of gas and dust, and the action takes place on a stage so remote that getting a detailed picture of the action requires extremely high angular resolution that interferometry is ideally placed to provide.

For more information contact Tim Bedding or Peter Tuthill.

Magnetic fields and turbulence

Magnetism plays a critical role in many areas of astrophysics, because it controls both the bulk flow properties of interstellar gas as well as the motion of individual charged particles. However, we know surprisingly little about the properties of the Galactic magnetic field. We are making a concerted effort to redress this situation, using the Faraday rotation of the diffuse polarised radio background as a new way to study structure and turbulence in magnetized gas.

Some of our current projects include:

• using the power spectra of rotation measures to map the turbulent cascade of ionised gas in the Galactic plane
• using the Faraday rotation of background point sources to map out the large-scale magnetic structure of the inner Galaxy
• analysing polarisation data on the Large Magellanic Cloud in order to carry out the most detailed study yet of the magnetic field of an external galaxy. 

Such data represent a whole new way of studying the ISM, and can allow a comprehensive study of interstellar magnetic fields on scales ranging from sub-parsec turbulence up to global galactic structure. 

Galactic structure

What can we learn about the formation processes of galaxies from studying the present structure of our own Milky Way, and nearby galaxies? Members of our group participate in international collaborations to observe structures in the outskirts of both the Milky Way and the Andromeda galaxies, thought to be remnants of interactions with smaller systems. Combining such observations with numerical simulations is an effective way for galaxy formation and evolutionary models to be tested. 

Galactic cannibalism occurs throughout the universe but, close to home, small dwarf galaxies are torn apart by the much more massive Milky Way and Andromeda Galaxy. Using telescopes from around the world, including the 10-m Keck telescope in Hawaii, we have mapped the tell-tale signs of tidal disruption and destruction, providing important clues to how large galaxies have grown over time. 

For more information contact Geraint Lewis.

Interstellar scintillation

The twinkling of stars, called scintillation, is due to fluctuations in the density of the air along the line of sight through the earth's atmosphere. Point-like radio sources, such as pulsars and quasars, also scintillate due to fluctuations in the electron density along the line of sight through the interstellar medium. Scintillation can lead to a change in the intensity of the source, a change in its apparent position, or both. 

Jean-Pierre Macquart and Don Melrose have developed a model for scintillations of radio sources based on scattering by discrete structures in the interstellar medium. This differs from the usual model that assumes a statistical fluctuation in density. Their approach was motivated by the thought that the rather large discrete structures required to explain Extreme Scattering Events (ESEs) may be extreme examples of a range of discrete structures common in the ISM. 

For more information contact Don Melrose.

Supernova remnants

We don't yet fully understand how stars explode and constraints on the many complicated processes which occur during core collapse are desperately needed. Since we rarely see a nearby star go supernova, our focus is on studying the aftermaths of supernova explosions, namely supernova remnants and young neutron stars, and in using these objects to infer the properties of the supernova, the progenitor star, and their surroundings.

This work is providing new insights into the micro- and macro-physics of the core-collapse process, on the properties of supernova progenitors, and on the mechanisms which produce the diversity we see in the resulting compact objects. 

For more information contact Anne Green, Dick Hunstead or Tara Murphy.

Near field cosmology

This research aims to place the nearest galaxies, members of the Local Group, within a cosmological context. A physical model is being developed describing the formation and evolution of the Local Group, with attention to radiative and gaseous processes, combining radiative hydrodynamics code with multiwavelength data.

For more information contact Joss Bland-Hawthorn

The role of super-massive black holes

We are building large data-sets containing thousands of quasars and radio galaxies with the express aim of measuring how they evolve and what the physical processes are which drive the evolution. We can do this by studying how individual sub-populations evolve, what their environments are and the how the black holes interact with their host galaxy. We will build on this with a broad range of multi-wavelength observations (from X-ray to radio) using state-of-the-art astronomical facilities in Australia and overseas. 

For more information contact Scott Croom, Dick Hunstead or Elaine Sadler.

Galaxy formation and evolution

The multi-parameter nature of galaxy formation has meant that much progress has been made over the last decade by conducting massive surveys of up to one million galaxies to be constructed. These have, in turn, allowed detailed statistical analyses to be made, where the correlation between the multitudes of physical parameters can be studied.

All of these major surveys use a single optical fibre to collect the light from each galaxy. Yet, galaxies are intrinsically complex, multi-component systems with multiple structural components (eg. disks, bulges, halos) and elaborate interactions between the dark matter, stars, gas and super-massive black holes they contain. The use of single apertures thus loses valuable information and adds confusing biases.

We are leading the SAMI Galaxy Survey to survey thousands of galaxies in 3D measuring the way gas and stars move with these galaxies as well as where star formation is currently ongoing and how and why accretion onto super-massive black holes is important. Key questions we hope to answer include:

• How does a galaxy’s environment influence its evolution? 
• How does gas get into and out of galaxies? 
• How is mass and angular momentum built up in galaxies?

The University of Sydney is also a key partner in new deep spectroscopic surveys such as the Galaxy And Mass Assembly (GAMA) project. This aims to get redshifts for hundreds of thousands of galaxies and combine this with multi-wavelength data to understand how galaxies are distributed and grouped within dark matter halos and measure the structural properties of galaxies.

For more information contact Scott Croom or Joss Bland-Hawthorn.

Gravitational lensing

Gravitational lensing is the bending of light by the gravitational field of a massive object. This phenomenon has a variety of astronomical applications. For example, it can be used as a natural telescope, magnifying distant sources into view or to probe the density profile of galaxies and galaxy clusters, testing dark matter theories.

The related field of microlensing has been used to search for low mass extrasolar planets, and to investigate the structure of quasars. Members of our group carry out computer simulations and observations of gravitational lensing.

Quasars, also known as quasi-stellar objects or QSOs, are luminous objects that are so distant that they appear pointlike in our images. When they are gravitationally lensed by an intervening galaxy, they can be multiply imaged. Often, assuming that the lens has a smooth mass distribution is adequate. However, in reality, galaxies are composed of stars and other compact objects, and are lumpy on small scales. Amazingly, this can actually change the brightnesses of the images, and these can vary with time in rather funky ways. We investigate these phenomena through the use of computational simulations.

For more information contact Geraint Lewis.

Dark energy

The WiggleZ team is using the Anglo-Australian Telescope to construct a huge redshift survey of ~400,000 galaxies at redshifts z~0.5-1.3.

The goal of this survey is to measure the "equation of state" of dark energy at high redshift. This is done by making high-precision measurements of the clustering of galaxies which ought to reveal the baryon acoustic oscillations (BAOs or baryon wiggles), a relic feature from the primordial Big Bang.

This encodes a fundamental physical scale whose size we can measure from the cosmic microwave background. Measuring this standard ruler at z=0.75 will give us the first high-precision measurement of dark energy independent of previous supernovae determinations. 

For more information contact Scott Croom.

Fundamental general relativity and cosmology

The theory of General Relativity is close to 100 years old and has been the preferred theory of gravity since its formulation by Einstein. Despite this, the understanding of General Relativity is not as advanced as might be expected, with few formal solutions existing and the physical interpretation of some of the mathematical results being unclear.

The Gravitational Astrophysics group conducts research into fundamental concepts in GR including the meaning and nature of expanding space and accelerated paths into black holes.

For more information contact Geraint Lewis.

Numerical cosmology

Members of our group study the implications of various dark energy models, primarily through N-body simulations, in order to increase the theoretical understanding of dark energy physics required in order to maximise the effectiveness of future surveys and instruments.

For more information contact Geraint Lewis.

Visit the Astrophotonics Research Group page for information.