5 April 2013
As the first results from the European Space Agency’s Planck satellite were being released last week, astronomers at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) near Johannesburg were working on a new radio telescope that will also shed new light on the earliest moments of the universe.
The C-Band All-Sky Survey (C-BASS) is a project to map the sky in microwave (short-wavelength radio) radiation. Like Planck, it will survey the whole sky, mapping out how bright the sky is, and also the orientation of the waves (called polarization). While Planck observes very short wavelengths, C-BASS observes longer wavelengths that are actually easier to observe from the ground.
“Because we want to observe at these longer wavelengths, the C-BASS telescope has to be much bigger than the telescope on Planck,” explains South African C-BASS team member Charles Copley. “The C-BASS dish is over seven metres across – much too big to launch on a rocket.”
In order to observe the entire sky, C-BASS needs to use two different telescopes, one in the northern hemisphere and one in the southern hemisphere. The northern telescope is already operating in California in the US, while the southern system is now undergoing final commissioning at HartRAO in South Africa.
After all the systems have been thoroughly checked out it will be moved to the Square Kilometre Array (SKA) site in the Northern Cape, where the full survey will be done.
The oldest light in the universe
C-BASS is the latest in a long line of efforts to measure the properties of the oldest light in the universe, the Cosmic Microwave Background (CMB). Tiny variations in the brightness and polarization of the CMB contain information about the conditions present in the early universe, only a few hundred thousand years after the Big Bang.
The universe then was nothing like what we see today – there were no planets, stars or galaxies. However, the seeds of all the structures we see today can be seen in the CMB. Understanding these beginnings provides us with an insight into the universe today.
The recently released Planck results focus on the CMB brightness, providing more accurate measurements than previous experiments. However, possibly the most exciting data is yet to come, in a year or so when Planck releases their CMB polarization measurements. These measurements may tell us about the physics of the universe when it was a tiny fraction of a second old.
However, in order to do this, the Planck mission is faced with a large problem – the Milky Way. Over a large fraction of the sky, any CMB polarization signal is completely obscured by radiation from our very own galaxy, the Milky Way. In order to successfully measure the CMB polarization, it is essential that astronomers understand this foreground radiation.
Re-purposing comms technology for science
This is where C-BASS will play a key role. Leader of the C-BASS team at Oxford University, Dr Angela Taylor, explains: “C-BASS acts like an extra frequency channel for Planck, hugely extending the range of radio wavelengths we have available. C-BASS will measure the polarization signal from our galaxy with great accuracy, and will hugely improve our ability to remove the galactic signal from Planck data, revealing the true CMB signal.”
Both the C-BASS telescopes, north and south, were originally built to communicate with satellites, and have been adapted by the C-BASS team to look into deep space.
This re-purposing of communications technology for science is also the idea behind the African VLBI Network (AVN) project, which plans to convert redundant satellite dishes across the continent into a giant radio telescope network. In fact, a twin of the southern C-BASS dish is being re-fitted right now to ship to Mozambique as part of the AVN.
South Africa’s growing role
C-BASS also highlights the growing collaboration between South Africa and the rest of the world in radio astronomy. South African astronomer Justin Jonas was a member of the group which conceived the project, and two South African students have studied for doctorates at Oxford University in the UK where the radio receivers were designed and built.
The southern receiver also uses digital hardware developed by the team working on the SKA precursor MeerKAT radio telescope in Cape Town.
C-BASS is a collaborative project between Hartebeesthoek Radio Astronomy Observatory, supported by the SKA project in South Africa, the Universities of Oxford and Manchester in the UK, the California Institute of Technology (supported by the National Science Foundation) in the US, and the King Abdulaziz City for Science and Technology in Saudi Arabia.