| Square Kilometre Array (SKA) | |
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An artist's impression of the central core of dish antennas of the SKA.
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| Location | Australia/NZ / South Africa |
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| Built | Phase 1 2019 Phase 2 2024 Phase 3 2022 onwards |
| First light | 2020 (planned) |
| Telescope style | Phased array |
| Collecting area | 1,000,000 m² |
| Website | skatelescope.org |
The Square Kilometre Array (SKA) is a radio telescope in development which will have a total collecting area of approximately one square kilometre.[1] It will operate over a wide range of frequencies and its size will make it 50 times more sensitive than any other radio instrument. It will require very high performance central computing engines and long-haul links with a capacity greater than the current global Internet traffic.[2] It will be able to survey the sky more than ten thousand times faster than ever before. With receiving stations extending out to distance of 3,000 km from a concentrated central core, it will continue radio astronomy's tradition of providing the highest resolution images in all astronomy. The SKA will be built in the southern hemisphere, in either South Africa or Australia, where the view of our own galaxy, the Milky Way, is best and radio interference least. With a budget of €1.5 billion, construction of the SKA is scheduled to begin in 2016 for initial observations by 2019 and full operation by 2024.[3][4]
The SKA is a global collaboration of 20 countries which is aimed to provide answers to fundamental questions about the origin and evolution of the Universe.[5]
In April 2011, Jodrell Bank Observatory (of the University of Manchester) in Cheshire, England was announced as the location of the headquarters office for the project.[6]
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The SKA will combine the signals received from thousands of small antennae spread over a distance of more than 3000 km to simulate a single giant radio telescope capable of extremely high sensitivity and angular resolution. The SKA will also have a very large field-of-view (FOV) with a goal at frequencies below 1 GHz of 200 square degrees and of more than 1 square degree (about 5 full Moons) at higher frequencies. One innovative development is the use of Focal Plane Arrays using phased-array technology to provide multiple FOVs. This will greatly increase the survey speed of the SKA and enable multiple users to observe different pieces of the sky simultaneously. The combination of a very large FOV with high sensitivity means that the SKA will transform the exploration of the Universe.
The SKA will provide continuous frequency coverage from 70 MHz to 10 GHz in the first two phases of its construction. A third phase will then extend the frequency range up to 30 GHz.
The frequency range from 70 MHz to 10 GHz, spanning more than two decades, cannot be realized using one design of antenna and so the SKA will comprise arrays of three types of antenna elements that will make up the SKA-low, SKA-mid and dish arrays:
The area covered by the SKA - extending out to ~3000 km - will comprise three regions:
The capabilities of the SKA will be designed to address a wide range of questions in astrophysics, fundamental physics, cosmology and particle astrophysics as well as extending the range of the observable universe.
A number of key science projects have been selected to be undertaken by the SKA and are listed below.
For almost ninety years, Einstein's theory of general relativity has precisely predicted the outcome of every experiment made to test it. Most of these tests, including the most stringent ones, have been carried out using radio astronomical measurements. By using pulsars as cosmic gravitational wave detectors, or timing pulsars found orbiting black holes, astronomers will be able to examine the limits of general relativity such as the behaviour of space and time in regions of extremely curved space. The goal is to reveal whether Einstein was correct in his description of space, time and gravity, or whether alternatives to general relativity are needed to account for these phenomena.
The sensitivity of the SKA in the 21-cm hydrogen line will map a billion galaxies out to the edge of the observable Universe. The large-scale structure of the cosmos revealed will give constraints to determine the processes resulting in galaxy formation and evolution. Imaging hydrogen through the Universe will provide a three-dimensional picture of the first ripples of structure which formed individual galaxies and clusters. This may also allow the measurement of effects hypothetically caused by dark energy and causing the increasing rate of expansion of the universe.[7]
The SKA is intended to provide observational data to fill the gap—the dark ages; between 300,000 years after the Big Bang when the Universe became transparent, and a billion years later when young galaxies are seen. By observing the primordial distribution of gas, the SKA should be able to see how the Universe gradually lit up as its stars and galaxies formed and then evolved.
It is still not possible to answer basic questions about the origin and evolution of cosmic magnetic fields, but it is clear that they are an important component of interstellar and intergalactic space. By mapping the effects of magnetism on the radiation from very distant galaxies, the SKA will investigate the form of cosmic magnetism and the role it has played in the evolving Universe.
The SKA will be capable of detecting extremely weak extraterrestrial signals if existing, and may even detect planets capable of supporting life. Astrobiologists will use the SKA to search for amino acids by identifying spectral lines at specific frequencies.
Suitable sites for the SKA need to be in unpopulated areas with guaranteed very low levels of man-made radio interference. Four sites were initially proposed in South Africa, Australia, Argentina and China.[8] After considerable site evaluation surveys, Argentina and China were dropped and two sites are now shortlisted:
Australia: The core site is located at Boolardy in Western Australia 315 km north-east of Geraldton[9] on a flat desert-like plain at an elevation of about 460 metres. The most distant stations will be located in New Zealand.[10] [11]
South Africa: The core site is located at at an elevation of about 1000 metres in the Karoo area of the arid Northern Cape Province, about 75 km north-west of Carnarvon, with distant stations in Ghana, Kenya, Madagascar, and Mauritius.
The final decision on the site will be made in 2012.
Many groups are working globally to develop the technology and techniques required for the SKA. Their contributions to the international SKA project are classified as either: Precursors, Pathfinders or Design Studies.
The Australian SKA Pathfinder, or ASKAP, is an A$100 million project to build a telescope array of thirty-six twelve-metre dishes. It will employ advanced, innovative technologies such as phased array feeds to give a wide field of view (30 square degrees).
ASKAP is being built by CSIRO at the Murchison Radio-astronomy Observatory site, located near Boolardy in the Mid West region of Western Australia. All 36 antennas and their technical systems are expected to be completed by 2013.[12]
MeerKAT is a South African project to build an array of sixty-four 13.5-metre diameter dishes as a world class science instrument and also to enable technology required for the SKA to be developed. KAT-7, a seven-dish engineering and science testbed instrument for MeerKAT, located near Carnarvon in the Northern Cape Province of South Africa is already up and running and the full MeerKAT array is expected to be ready by 2015-2016. The dishes will be equipped with a number of high performance single pixel feeds to cover frequencies from 580 MHz up to 14 GHz.[13]
The Allen Telescope Array uses innovative 6.1m offset Gregorian dishes equipped with wide band single feeds covering frequencies from 500 MHz to 11 GHz. The 42-element array now in operation is to be extended to 350 elements. The dish design has explored methods of low-cost manufacture.[20]
LOFAR is a €150 million Dutch-led project building a novel low frequency phased aperture arrays spread over northern Europe. An all-electronic telescope covering low frequencies from 10 to 240 MHz which has been coming online through 2009 to 2011. LOFAR will demonstrate crucial processing techniques vital to the SKA.[21]
The Technology Development Programme, or TDP, is a US$12 million programme to specifically develop dish and feed technology for the SKA. It is operated by a consortium of universities led by Cornell University and will be completed in 2012.[25]
The SKA was originally conceived in the early 1990s with an international working group set up in 1994. This led to the signing of the first Memorandum of Agreement in 2000. Considerable early development work then followed. This culminated in the commencement of PrepSKA in 2008 leading to a full SKA design in 2012. Construction of Phase 1 will take place from 2016 to 2019 providing an operational array capable of carrying out the first science. Phase 2 will then follow for completion in 2024 providing full sensitivity for frequencies up to 10 GHz.
The SKA is projected to cost €1.5 billion for phases 1 and 2 completing in 2024, this includes €300 million for Phase 1 completing 2019. The funding will come from many international funding agencies. Preliminary expectations are that Europe, the United States and the rest of the world will each contribute a third of the project's funding. The SKA and the European Extremely Large Telescope (E-ELT) are the two flagship facilities for ground-based astronomy in the future. They are equal high priority projects in the ASTRONET roadmap for European astronomy.
In 2010, concerns were raised over increased radio interference at the South African site due to an application by Royal Dutch Shell to explore the Karoo for shale gas using hydraulic fracturing.[26] The Astronomy Geographic Advantage Act, passed by South Africa in 2007, which outlaws certain radio related activities in astronomy advantage areas may possibly prevent radio interference associated with mining activities within range of the designated SKA site.