The Dark Universe


Dr Cullan Howlett
Prof Tamara Davis Dr Cullan Howlett
Theme Leader Theme Scientist

Over the past decade, astronomers have arrived at the uncomfortable conclusion that 96% of the Universe is not made of normal atomic matter, but consists of two separate as-yet unexplained phenomena: “Dark Energy” and “Dark Matter”. The current standard model to describe the Universe is one where the cosmos is geometrically flat, and is dominated by Einstein’s cosmological constant, Λ (corresponding to the vacuum energy of empty space), and by cold dark matter (CDM, widely assumed to be an undiscovered class of massive particle). A series of landmark experiments, several of which were performed by CAASTRO’s investigators, have confirmed many of the predictions of “ΛCDM” cosmology. However, fundamental doubt remains over the validity of ΛCDM, because there is no physical understanding of either Dark Matter or Dark Energy. Through CAASTRO, we are carrying out a series of coordinated wide-field surveys of the sky, aimed at rigorously testing the ΛCDM paradigm.

First, we are searching for new, nearby Type Ia supernovae. Statistics on the relative brightness of these explosions compared to more distant supernovae can allow a precise measurement of the rate at which the Universe’s expansion is accelerating due to Dark Energy, providing the most precise test yet of ΛCDM cosmology.

Second, we are performing all-sky measurements of large numbers of galaxies in both the radio and optical bands, in order to derive precise estimates of their distances, velocities and 3D distributions in space. Combining this information with a substantial new body of simulations and theoretical tools, we aim to measure the velocity field of galaxies out to 10% of the Hubble radius. With these data we can measure the subtle variations in the otherwise smooth expansion of the Universe that are a specific prediction of ΛCDM, thereby deriving a map of Dark Matter on the largest scales ever performed. We can use these observations of “cosmic flows” to test Einstein’s theory of gravity in the weak field regime, to test whether Cold Dark Matter behaves as predicted, and to determine whether structure in the Universe is growing as expected for a cosmos filled with Dark Energy in the form of a cosmological constant.

Watch the theme video profile as presented by Professor Brian Schmidt, "The Dark Universe" Theme Leader 2011-2013. The projects associated with CAASTRO's Dark Universe include:

Peculiar Velocity Surveys: Measuring the distribution of Dark Matter on large scales using deviation from uniform expansion.
Type Ia Supernovae: Probing Dark Energy with precise measurements of the Universe's expansion history.
Large Scale Structure: Using galaxy redshift surveys to map the expansion history and growth of structure in the Universe.
Dark Theory and Simulations: Maximising the power of observations through groundbreaking theoretical simulations.