Will the SKA telescope probe the "Dark Ages" of the universe from southern skies?

Southern Africa will be receiving a boost in radio astronomy research if South Africa's bid to host the Square Kilometer Array (SKA) telescope, is successful. SKA, billed to be the world's largest radio telescope will allow scientists to see into the early part of the universe, as it was  13 billion years ago.

South Africa SKA logo(SKA) was conceived as a new international project to meet the future needs of radio astronomers. One of the prime objectives of the SKA is to probe the so-called "Dark Ages", when the early universe was in a gaseous form before the formation of stars and galaxies. At present astronomers do not have the necessary tools to observe radiation from this period of the universe, which extends from about 300 000 years till 1 billion years after the Big Bang.

The science behind SKA

Astronomers explore the universe by passively detecting electromagnetic radiation and cosmic rays emitted by celestial objects. The earth's atmosphere shields us from much of this radiation so modern astronomy is done from large optical telescopes on high mountains or from orbiting satellite observatories.

Radio astronomers, on the other hand, concentrate on the relatively long wavelength (or low frequency) radio waves that penetrate the atmosphere with little impediment or distortion. These radio signals have frequencies between about 30 Megahertz and 40 Gigahertz, or equivalently, wavelengths from 10 metres down to 7 millimetres.

Because electromagnetic radiation travels at a fixed speed of about 1.08 billion kilometres per hour, very distant objects are observed as they were in the distant past. Astronomers are therefore able to look back in time to observe the early stages of the evolution of the universe.

Radiation reaching us from the "Dark Ages" has travelled a huge journey through space, and is in the form of radio signals emitted by the neutral hydrogen gas that dominated the universe during this period. The signals are, however, extremely faint and require a telescope with a large area, efficient antennas and sensitive radio receiver is required.

The SKA is billed to do just this. SKA will have a receiving surface of a million square metres, one hundred times larger than the biggest receiving surface now in existence. This huge surface will be composed of many small antennas, divided into a dense inner core array which becomes more diffuse with increasing radius.

Many details still have to be worked out, and the peripheral antennas could be 1 000 km from the core, or 5 000 km, or even 10 000 km, making the SKA an intercontinental system. The signals received by each and all of these antennas will be combined to form a single big picture.

The SKA will map the time evolution of the primordial gas as it condenses to form the first objects in the universe. It will also chart the development of these adolescent stars and galaxies, which will provide us with information about our own origin. The atoms in our bodies, our planet and our star were formed by the nuclear reactions that powered these early stars.

Location

Proposed locations for the SKA telescope in South AfricaThe instrument cannot be located between 25°N and 25°S, as that is the region of the equatorial electrojet, the part of the ionosphere that is most sensitive to variations in the sun's illumination, and which can disrupt the electromagnetic radiation passing through it, which radio astronomers would wish to observe. It can also not be positioned too close to the poles, for then it would not be able to cover enough of the sky. While the core element must be in a radio reserve, it must nevertheless not be too far away from major centres.

Furthermore, in order to see into the early universe astronomers need a telescope able to receive radio emissions in the range of a few hundred megaHertz, a frequency band now crowded on earth with TV and cellular telephone transmissions. The core element of the SKA should be in the centre of a 100 km diameter radio interference-free region.

The South African SKA has identified three sites in the Northern Cape of the country, the Kalahari, the Karoo and Namaqualand, as ideal locations for SKA radio telescope, each with a diameter of 150 km.

Some of the most important reasons why the Northern Cape is ideal includes the "radio quietness" of the area (i.e. minimum radio interference from cell phone networks, etc), low population density and suitable topography.

The province of the Northern Cape occupies close to 30% of the total land surface of the country. This province alone is three times the size of Germany, but is sparsely populated with well under a million people.

Bidding

South Africa is competing with countries including Australia, Brazil, China and the US to host the SKA.

The South African proposal to host the Square Kilometre Array (SKA) radio telescope passed its first hurdle with flying colours when it submitted its comprehensive proposal, to the International SKA Steering Committee (ISSC) at the end of May.

Professor Justin Jonas (Director of the Hartebeesthoek Radio Astronomy Observatory and Professor of Physics and Electronics at Rhodes University, and South Africa's representative on the International SKA Committee) and Dr Bernie Fanaroff (Project Manager) represented South Africa at this meeting.

Although all countries proposals passed this first evaluation, there was a clear consensus that a southern hemisphere site for the SKA was preferred. The southern hemisphere has distinct advantages in that the entire Milky Way galaxy is only visible from southern skies and also that it is already successfully home to other major astronomical facilities, such as the SALT and HESS telescopes.

The international SKA steering committee visited the proposed South African sites in mid January this year to evaluate the sites and the countries infrastructure. A final decision is expected during 2005, while construction on the USD 1 billion SKA will probably start in 2010.