African eyes on the universe

 

The Southern African Large Telescope is
housed at the Sutherland Observatory in
the remote Northern Cape province.
(Image: Graeme Williams,
MediaClubSouthAfrica.com. For more
free photos, visit the image
library
.)

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South African Astronomical Observatory
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In the remote Northern Cape, the largest telescope in the southern hemisphere is producing crystal-clear images from deep space, thanks to the province’s unique climate and topography. A semi-desert region, the Northern Cape is far less developed than the rest of South Africa, with vast stretches of arid bushland between its cities and towns.

Yet this emptiness is part of the reason the province has become a major hub for astronomical observations, because there’s not much in the way of artificial light or radio waves to interfere with optical and radio astronomy.

The Southern African Large Telescope near the town of Sutherland is not only the largest in the southern hemisphere, it’s among the largest 10 in the world. South Africa is also one of the two global finalists in the bid to host the massive Square Kilometre Array, which, if the country wins, will also be located in the Northern Cape.

In addition to its remoteness, the Northern Cape has a low topography suited to radio astronomy, with mountains providing extra shielding against radio waves from distant metropolitan areas.

The southern hemisphere is the perfect place for astronomy, because it sees more of the sky than the north. And South Africa’s sophisticated infrastructure and first-class science and technology sector gives it the capacity for some of the best astronomy in the world.

The Southern African Large Telescope

On a hilltop in a nature reserve in the Northern Cape, near the small town of Sutherland, is a masterpiece of modern astronomical engineering. The Southern African Large Telescope (SALT) is the largest optical telescope in the southern hemisphere, and equal to the largest in the world. Gathering more than 25 times as much light as any existing African telescope, SALT can detect objects as faint as a candle flame on the moon.

Opened in November 2005, SALT is one of the leading instruments of its kind, enabling local and international scientists to see distant stars, galaxies and quasars a billion times too faint to be visible to the naked eye.

The telescope is similar to the Hobby-Eberly Telescope in Texas, but has a redesigned optical system – an achievement of South African astronomer Dr Darragh O’Donoghue – that uses more of its mirror array.

Eleven metres in diameter, this array enables imaging, spectroscopic, and polarimetric analysis of the radiation from astronomical objects out of reach of northern hemisphere telescopes.

SALT is facility of the South African Astronomical Observatory, the country’s national optical observatory. Its won support from the country’s government for both its advanced astronomical technology and the host of spin-off benefits it could bring to the country. It has become an icon for what can be achieved in science and technology in the new South Africa.

Funding and partners

A talented team of local engineers and scientists succeeded in building SALT on a rapid – for big telescope projects at least – five-year timescale. The cost of construction was kept to within the original budget of US$20-million defined in 1998, even before the final designs were completed.

The cost of the construction and operation of the telescope over its first 10 years is a total of US$36-million: US$20 million for the construction of the telescope, US$6 million for instruments and US$10 million for operations. A third of this funding is from South Africa, and rest from the project’s partner countries: Germany, Poland, the United States, the United Kingdom and New Zealand.

The institutional partners of the SALT consortium are:

Armagh Observatory
Keele University
University of Central Lancashire
University of Nottingham
Open University
University of Southampton

In 2007, the two new partners joined the consortium:

Building the telescope

In the year 2000, on the first day of southern hemisphere spring, a few hundred people gathered on the hilltop near Sutherland for the SALT ground-breaking ceremony. After nearly four years of construction, in March 2004, installation of the massive mirror began. The last of the 91 smaller mirrored hexagon segments was put in place in May 2005.

First light with the full mirror was declared on 1 September 2005, with the telescope obtaining images of globular cluster 47 Tucanae, open cluster NGC6152, spiral galaxy NGC6744, and the Lagoon Nebula being obtained. SALT was officially opened by President Thabo Mbeki on 10 November 2005.

Both SALT and the Hobby-Eberly Telescope have unusual designs for optical telescopes. The primary mirror is composed of an array of mirrors designed to act as a single larger mirror. Each SALT mirror is a hexagon, one metre in size, with the array of 91 identical mirrors together making a hexagonal-shaped primary mirror 11metres by 9.8 metres in size. Each of the smaller mirrors can be adjusted in order to properly align to make them function as a single mirror.

SALT’s instrumentation for includes the SALT Imaging Camera (SALTICAM), designed and built by the South African Astronomical Observatory (SAAO); the Robert Stobie Spectrograph, a multi-purpose longslit and multi-object imaging spectrograph and spectropolarimeter, designed and built by the University of Wisconsin-Madison, Rutgers University, and SAAO; and a fibre-fed High Resolution Spectrograph, designed by the University of Canterbury, New Zealand.

The telescope has a 1.5-Mbit internet connection, feeding to what is termed the “beach-head”, from where other institutions can access the data.

An artist’s impression of the Square
Kilometre Array. To give a sense of the
scale, the small object in the shadow in
the foreground is a car.
(Image: SKA South Africa)

The Square Kilometre Array

South Africa has been shortlisted to host one of the biggest and most sophisticated scientific instruments in the world, the Square Kilometre Array (SKA) – a future generation international radio telescope that will enable astronomers to probe the early evolution of our galaxy.

In September 2006 the International SKA steering committee in the Netherlands announced in September 2006 that South Africa and Australia had been shortlisted as sites for the SKA, a set of thousands of antennae that, put together, would cover a square kilometre.

The network of dishes will be at least 50 times more powerful than any telescope yet built.

If South Africa were to win the bid, it would bring a massive injection of expertise and economic activity to the Northern Cape, with benefits for the local aluminium, computer, communications, electronics and steel industries.

The SKA project will cost in the region of US$1-billion, and could generate as much as R500-million in foreign investment for South Africa.

South Africa and Australia beat bids from Argentina and China to make the SKA shortlist. A final decision is expected by 2008, while construction on the SKA will probably start in about 2013 and be completed by about 2019.

Global design programme

In 2006, European funding was agreed for a €38-million (US$46-million) global programme to design the Square Kilometre Array.

The four-year SKA Design Studies programme will see astronomers in Australia, South Africa, Canada, India, China and the US collaborating closely with their colleagues in Europe to formulate the most effective design and develop the technology required.

Designing and then building such an enormous and technologically advanced instrument is beyond the scope of individual nations, which is why the project aims to harness the ideas and resources of countries across the world.

The Karoo Array Telescope

In the meantime, South Africa has begun work on a SKA prototype known as the Karoo Array Telescope (KAT), with technology that will parallel that of the SKA.

Construction on this smaller version of the SKA is expected to be complete in 2008/9, and will entail cooperation with some of the other countries involved in the SKA project to ensure efficient technology transfer.

While the KAT will have about 1% of the SKA’s receiving capacity, it will still be a powerful radio telescope in its own right. It will also prove that South Africa is committed and ready to host the SKA.

Radio quietness

A radio telescope has to be as far away as possible from artificial sources of radio waves, such as cellphone and radio networks.

Working with the Independent Communications Authority of South Africa (Icasa) to measure radio frequency interference levels in some of the most remote parts of the country, the South African SKA team has identified three sites in the Karoo in the Northern Cape, all three boasting radio interference-free zones of 150 kilometres, far exceeding the SKA requirement of 100km radio interference-free areas.

The Northern Cape sites also have a low topography suited to the SKA, with mountains providing extra shielding against radio waves from remote metropolitan areas.

The southern hemisphere also has the astronomical advantage of being exposed to more sky than the north. South Africa is also on the same longitude as Europe, so it sees the same night sky, and scientists can easily link up with facilities there.

In addition to the radio quietness of its sites, South Africa has the capabilities and track record to host, support and contribute to the science that will be generated by largest radio telescope ever built.

Radio signals from the past

The core element of SKA should be in the centre of a radio interference-free region at least 100 kilometres in diameter. This is because radio emissions from the early universe – which the SKA will seek to capture – are in the range of a few hundred megaHertz, a frequency band now crowded on earth with TV and cellular telephone transmissions.

To pick up these radio emissions – literally, radio signals from the past – the SKA will have a receiving surface of one million square metres, 100 times larger than the current biggest surface.

The huge receiving surface will consist of many small antennae, divided into a core element and a periphery. The peripheral antennas could be between 1 000 and 10 000 kilometres away from the core element, making the SKA an intercontinental system.

The signals received by all these antennae will be combined to form one single, big picture.

The result will be an instrument capable of probing the secrets of the very early universe, just after it began about 14 billion years ago – so science tells us – with the Big Bang.

Listening to the early universe

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 earth’s atmosphere with little impediment or distortion.

Because electromagnetic radiation travels at a fixed speed of about 1.08 billion km/h, 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.

Most existing radio telescopes were built 10 to 30 years ago. For radio astronomy to progress, a new telescope with 100 times the collecting surface of existing telescopes will be needed in about 10 years’ time.

The SKA will 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 one billion years after the Big Bang.

Radiation reaching us from these 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 the planned sensitivity of the SKA to be detected.

The SKA will map the time evolution of this cosmic web of 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.

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