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.
 (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
 The 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.
More information:
Website: http://www.ska.ac.za
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