Solar Astrophysics

The processes underlying sun spots, solar flares, coherent solar radio emissions and the structure of the Sun’s magnetic field are still poorly understood today. Three Australian universities are seeking to understand our nearest star in greater detail.

Astronomers at the Monash Centre for Astrophysics (MoCA) are using a technique called Helioseismology to probe the magnetic structure of the solar surface and the fields that produce sunspots. Helioseismology utilizes sound waves that propagate throughout the Sun to measure its invisible internal structure and dynamics. As the Sun oscillates light emitted from the surface is Doppler-shifted producing a periodic pattern of nodes and antinodes . The periods of these waves depend on their propagation speeds and the depths of their resonant cavities allowing scientists to probe the temperature, chemical composition, and motions from just below the surface down to the very core of the Sun

Through 3D radiative-hydrodynamical numerical simulations with supercomputers, researchers at the Research School of Astronomy and Astrophysics at ANU are investigating the nature of solar convection. These simulations are highly successful in reproducing key observational diagnostics such as spectral line shapes and asymmetries, helioseismological constraints and granulation topology and flow properties.

Solar flares are dynamic events in which magnetic energy is released in the solar corona. Many aspects of the flare phenomenon remain poorly understood. Recent work on flares at the RCfTA in the University of Sydney includes the construction of a model for flares in terms of reconnection between current-carrying magnetic flux tubes, analysis and modelling of various aspects of flare statistics, and investigation of different methods for calculating magnetic field configurations associated with flares.

Coherent solar radio emissions are produced during flares and while coronal mass ejections (CMEs) are moving through the corona and solar wind. Despite over 50 years work, detailed theories are only now becoming available to confront data from spacecraft and ground-based observatories. The Space and Solar Physics Group at the University of Sydney is studying the burstiness of the radio emission in terms of ‘complex systems’ research (specifically the so-called stochastic growth theory) and developing quantitative theories for radio emission associated with CME-driven shocks (including electron acceleration by the shock and the plasma physics of the emission processes). One current focus is the development of dynamic spectra and other theoretical predictions for comparison with observations, including those for the upcoming STEREO spacecraft and LOFAR telescope.

One way to learn more about the Sun is to study other stars with similar properties, the so-called “solar-type” stars. Research at the University of Southern Queensland includes observations of stars representing an early phase of solar evolution. These young stars reveal activity that is far more intense than the current level of solar activity and demonstrate the importance of magnetic activity to the Sun’s early evolution. Active solar-type stars, some young, some more mature, can also provide fundamental new knowledge for understanding the dynamo processes that produce the magnetic fields, activity and variability of stars like our Sun.

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