Broadly speaking, astrophysics is the study of how the various parts of the universe work- stars, planets, gas, dust, galaxies; how they form, how they develop and how they behave.
When the field of astrophysics began in the late 19th century, only the optical wavelengths were available for study. Over the years, the range was extended beyond the optical and into infra-red and ultra-violet, to radio, to X-rays and gamma-rays, and to include particle physics.
Associated with the increase in the range of energies that we can observe has been an expansion in the hardware in use by astrophysicists. There are ground-based and space-based instruments; from things that look like the classic idea of what a telescope looks like, to huge underground caverns filled with water; from classic radio dishes to arrays of antennae. All of these are used to observe and examine the universe around us.
The Adelaide High-Energy Astrophysics Group has evolved over the years, broadening both the range of energies it studies and the extent of its collaborations across the globe. HEAG now observes the universe via the use of electromagnetic waves from radio through to gamma-rays, as well as particles.