The international Square Kilometre Array (SKA) radio telescope – which is to be jointly hosted by South Africa and Australia, with, later, outstations in other countries – may not yet exist, but international scientific working groups are already deciding what projects to use it for when its first phase is completed in 2023. The SKA is being developed by the international SKA Organisation, which currently has 11 member countries.
One of these groups is the Cosmology Science Working Group, which is currently chaired by University of the Western Cape (UWC) SKA research professor Roy Maartens. (Cosmology is concerned with the study of the evolution and structure of the universe as a whole.) Another UWC researcher, Professor Mario Santos, is also a member of this group. Recently, the group published a number of papers containing research project proposals for the SKA.
One of the proposed projects is the creation of the biggest-ever map of the universe. Up to now, mapping the universe has been a slow process, involving the detection of faint radio waves from distant galaxies and observing each galaxy long enough to determine key properties such as its distance from earth. The big advantage of this method, which has mapped only about a million galaxies so far, is that is very accurate and results in very detailed three-dimensional (3D) maps of the distribution of matter in the universe.
But the cosmology working group is proposing to use the SKA to carry out a very different type of cosmological mapping, called intensity mapping. The instrument would be rapidly and repeatedly scanned across the sky, surveying a much larger portion of the sky in a much shorter period. The resulting map would, on the other hand, lack detail. “This will only give us a low-resolution map, but that’s already enough to start answering some serious questions about the geometry of the universe and the nature of gravity,” explained Santos. This type of experiment has not been done before. It will take only about two years to complete.
“The survey we are proposing will measure the emitted radiation from all the hydrogen atoms spread across the universe without actually detecting galaxies,” he elucidated. “This will make it easier to survey all of the sky across cosmic times, allowing Phase 1 of the SKA to become an extremely competitive cosmology machine. By making these huge 3D maps of the universe, we will be able to test the limits of general relativity and maybe find some signature of new physics on these large scales which can shed light on the true nature of dark energy. Moreover, we can also look for imprints of what happened at the very beginning of the universe.
It will be like making a movie of the universe from a young age, when it was only about two-billion years old, [up to] today when it is about 14-billion years old,” noted Maartens. “The movie will be low resolution but enough to test the fundamentals of cosmology.”
The papers written by members of the Cosmology Science Working Group are part of a process that will, with project proposals from the other working groups, result in the publica- tion by the SKA Organisation of a science book containing some 130 papers covering the science that the SKA will be doing. This book will be published in the northern summer of this year. This activity is being coordinated by SKA Organisation science director Dr Robert Braun. “It’s rewarding to see all these papers being published, thanks to the hard work put in by all the science working groups,” he said. “The wide range of science being covered in them is testimony to the SKA’s potential as a twenty-first century facility to revolutionise many areas of study in astrophysics, but also in physics, astrochemistry and beyond.”
The 11 SKA member countries are Australia, Canada, China, Germany, India, Italy, the Nether- lands, New Zealand, South Africa, Sweden and the UK. SKA Phase 1 will have a collecting surface equivalent to 15 soccer pitches and will in one day collect data equivalent to several days traffic on the worldwide Web. Phase 2, which should be completed by the late 2020s, will be ten times bigger.