Far outback in Western Australia, 32 tiles—flat, stationary sensors—each carrying 16 dipole antennas have begun collecting scientific data.
These first tiles will ultimately form part of a much bigger array of 512 tiles, the Murchison Widefield Array (MWA)—Australia’s second Square Kilometre Array (SKA) demonstrator project. Like CSIRO’s Australian SKA Pathfinder (ASKAP), the MWA is being built at the remote, radio-quiet Murchison Radio-astronomy Observatory (MRO).
The MWA is designed to study celestial radio sources at low frequencies, a poorly known part of the radio spectrum between 80 and 300 megahertz. The array is ‘steered’ electronically, which means the direction the telescope points depends entirely on how the signals from its stationary antennas are combined and processed.
The facility is a collaboration between several universities and research institutions in the US, Australia and India. The site for the full telescope was prepared in 2010, and the final array will begin operating within a couple of years, says MWA Board Vice Chair, Steven Tingay of Curtin University, the International Managing Organisation for the $30 million facility.
As the working tiles are being tested for the final array, the MWA itself is testing technologies to be used when the world’s largest telescope, the SKA, is built. But the MWA will be a powerful instrument in its own right, and already has been earmarked for three significant research projects.
One will take measurements of the Sun and material in the plasma surrounding it; another will survey low-frequency radio emissions across the sky, particularly those that are transient. And the third will detect and analyse hydrogen from the ‘Epoch of Re-ionisation’ in the early Universe when the gas changed from being almost neutral to extensively charged or ionised.
When did the first stars begin to shine?
After the Big Bang, the Universe was a cold, dark place—until the first galaxies and stars formed and shone their light into the gas that pervaded space, resulting in the re-ionisation of cosmic hydrogen.
The state of the Universe during re-ionisation has been simulated using computer models by Stuart Wyithe, a physicist at the University of Melbourne. Stuart is probing to determine exactly when and how re-ionisation occurred, what kind of stars were responsible and whether black holes were involved.
“We have an idea of what the Universe was made of, and we have a theory of gravitation and how structure formed,” says Stuart. “The goal is to use that framework to try and understand how the first galaxies interacted with the intergalactic medium around them.”
That’s where the MWA comes in. “Current Hubble [Space Telescope] pictures of the early Universe do not reveal enough star formation to have re-ionised the Universe, so there must have been something else contributing to it,” adds Stuart. “They could be less luminous galaxies, or they could be something else.”
Stuart and his colleagues now plan to use the MWA to peer back toward the Universe’s ‘Dark Ages’, to see if their computer simulations are right.
Stuart received one of the Prime Minister’s Prizes for Science in October 2011—the Malcolm McIntosh Prize for Physical Scientist of the Year.
PHOTO 1: THE MURCHISON WIDEFIELD ARRAY IS A TELESCOPE WITH NO MOVING PARTS. CREDIT: DAVID HERNE, ICRAR.
PHOTO 2: A HUBBLE SPACE TELESCOPE IMAGE OF SOME OF THE EARLIEST GALAXIES THAT MAY HAVE BEEN RESPONSIBLE FOR ‘LIGHTING UP’ THE COSMOS. CREDIT: NASA, ESA, R. WINDHORST (ARIZONA STATE UNIVERSITY) AND H. YAN (SPITZER SCIENCE CENTER, CALTECH).