The world's largest radio telescope is taking shape. The Square Kilometre Array (SKA) will be of a scale never seen before, and with the first prototype dish recently unveiled, the search for answers to some of the most fundamental questions about the universe and its origins is set to begin. So what exactly is the SKA and what will it teach us about the universe?
Since the first radio signals were detected from space by Karl Jansky in the 1930s, astronomers have used radio waves emitted from a range of celestial bodies and objects to explore our universe. These waves are invisible to our eyes, but can be picked up and converted into images by radio telescopes at distances millions and billions of light years away. Radio astronomy has led us to some amazing astronomical discoveries, such as pulsars, exoplanets and the cosmic microwave background (a remnant signal left over from The Big Bang).
The Square Kilometre Array is set to take this to a new level. Stretching over dusty, flat plains across South Africa and Western Australia, the SKA will combine a host of different antenna technologies to map the sky hundreds of times faster than today's best radio astronomy facilities. When it begins operation in 2024, it will be able to detect radio signals emitted by cosmic sources billions of light years away with an unparalleled sensitivity.
In an international collaboration between 20 countries, the Square Kilometre Array will change the scale and scope of astronomical observations worldwide.
The International Union of Radio Science (URSI) created the Large Telescope Working Group in 1993 to establish scientific goals and specifications for an innovative radio observatory. This eventually led to the formation of the SKA Organisation in 2011.
The name reflects the original intentions to construct a distributed array of antennas with a collecting surface of up to one square kilometer (0.38 sq mi), though the concept has since been expanded and the full SKA will be much larger than this. Today, the Square Kilometre Array project involves more than 500 engineers, making it the world's largest public science data enterprise currently in operation.
With numerous countries, including Argentina, China, South Africa and Australia, originally expressing interest in hosting the SKA, the list was eventually whittled down to South Africa and Australia, with both those countries given the nod in 2012 to co-host the project. Additionally, Manchester in the UK received approval to serve as the SKA's headquarters.
For the South African facility, initial plans canvassed one site in the Karoo, a semi-desert region in southwest of the country. Its remote location ensures that human-generated radio waves won't interfere with those being gathered from the natural universe. Meanwhile, the Murchison Radio-astronomy Observatory, located in a radio-quiet shire in Western Australia, was selected as the site for the Australian facility.
Precursor facilities are already constructed at each site to assist in improving antenna designs over the next decade. The South African MeerKAT and HERA, as well as Australia's Murchison Widefield Array (MWA) and CSIRO's Australian SKA Pathfinder (ASKAP) carry out scientific studies that are applicable to the main array, as well as testing developments in technology that are vital to general functionality of the SKA.
Other systems across the world, such as the Allen Telescope Array in California, the UK's e-MERLIN and the Low Frequency Array in The Netherlands, will be used in SKA-related technology and research.
The first prototypes
Although the major construction stage is still a few years away, the first fully assembled prototype of an SKA dish was revealed in China on February 6, 2018, by the Vice Minister of the Chinese Ministry of Science and Technology.
The 15-m (49-ft) diameter dish was the combination of a three-year international collaboration. Parts were sourced from China, Germany and Italy, with final assembly carried out by the 54th Institute of China Electronics Technology Group Corporation (CETC54).
Leading the design and production process for this prototype, CETC54 concentrated on refining vital components, such as the main reflector, sub-reflector and pedestal.
"This is a mature method developed by CETC54," says Wang Feng from the Joint Laboratory for Radio Astronomy Technology (JLRAT). "Applied to the SKA dish, it allows us to achieve and maintain the dish surface to a very precise surface-accuracy level as well as consistency for all panels."
At MT Mechatronics (MTM) in Germany, engineers have been busy manufacturing precise hardware and electronics to move the dish, while the Società Aerospaziale Mediterranea (SAM) in Italy has worked on the feed indexer, an electro-mechanical part that will allow various receivers to be adjusted and aligned with the optics of the dish as required for detailed observations.
"The feed indexer is a very innovative part of the dish, the first of its kind," says Renato Aurigemma, SAM team coordinator. "We've got stringent requirements, as the indexer needs to move with high accuracy to position the receivers with sub-millimetric precision, and it also needs to be able to sustain heavy loads, with for example the Band 1 receiver alone weighing 165 kg (364 lb)."
The dish is one of two final designs that will be tested for performance and calibration ahead of an Early Production Array (EPA) that is expected to be built on the South African site in 2019. This EPA will allow engineers to identify any technical issues before full-scale production is underway.
Phases I and II
Phase I of the SKA is currently being implemented through pre-construction stages at several factories around the world, with the first astronomical observations planned for 2019.
The South African site will host a total of 200 radio dishes with a medium frequency range of 350 MHz – 14 GHz. Radiating out from three spiral arms over an area spanning 33 sq km (12.7 sq mi), these telescopes will have four times more resolution, five times more sensitivity and the ability to map the sky 60 times faster than the Karl G. Jansky Very Large Array (JVLA) in New Mexico, a multi-dish observatory that is currently the best telescope working at similar frequencies.
Research conducted at the South Africa site will focus on the study of gravitational waves and pulsars, as well as continue the search for extra-terrestrial life in the Milky Way by observing the thermal emissions from the habitable zones around young stars.
On the other side of the globe, the ochre dustbowl of Western Australia will become the home for 130,000 dipole antennas at more than 500 stations, each with a low frequency range of 50 Mhz – 350 Mhz. This aperture array, also set out in three arms spiraling from a concentrated center, will provide 25 percent better resolution, be eight times more sensitive and map the sky 135 times faster than the best similar telescope – the Low-Frequency Array (LOFAR) in The Netherlands.
The baseline, or distance between each telescope, is precisely calculated using the time difference between the arrival of radio signals at each receiver. The longer this distance, the sharper the resolution – with maximum distances of 65 km (40 mi) between instruments at Murchison and 150 km (93 mi) at Karoo, objects billions of light years away will be identified in unprecedented detail.
Astronomers based here will investigate the mysteries of dark matter and dark energy, as well as study the Epoch of Reionization – a time around 13 billion years ago when the emergence of stars and other luminous objects cleared the fog of neutral hydrogen atoms and gave us the transparent universe we see today.
We spoke to Dr Cathyrn Trott, a Senior Research Fellow at the International Centre for Radio Astronomy Research and member of the SKA Science and Engineering Advisory Committee about this transformational scientific research.
"The key feature of the SKA is that it has so much collecting area over numerous small spaces on the ground, so that means you can collect photons of light over a very wide area, which makes it quite sensitive to weak signals from the universe," says Dr Trott. "This signal from the Epoch of Reionisation, for instance, is exceptionally weak, it is orders of magnitude weaker than anything else that we see in the sky at the moment … and what we're looking for is actually deeply embedded in the universe, so we need to get away from the city to a pristine night sky environment, and that's what the Murchison region provides.
"The SKA is going to be revolutionary compared with current telescopes because it's going to be built in such a way that we can extract even more information out of the data we receive from it," says Dr Trott. "Computing, and the ability to process data very quickly is another major advance."
Phase II construction is slated for the early 2020s. The long-term ambition is to increase the strength of the telescopes to a high frequency range, construct several million dipole antennas in Western Australia and involve eight African partner countries – Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia and Zambia – in hosting smaller sites in the future.
Presently, the design phase of these telescopes alone has cost more than €150 million (US$182 million), with an estimated total cost for Phase I expected to be in the order of €674 million (US$813 million). Between 2018 and 2027, figures could be close to €1.8 billion (US$2.2 billion), accounting for general research, initial construction and early operations. The SKA will have an estimated lifetime of about 50 years from its first observations.
Inspiring future generations
Pure scientific research isn't the only benefactor of the initiative. As one of its key foundations is global collaboration, the investment into construction and operation of the SKA will continue to strengthen ties between foreign agencies. Outreach programs run by the SKA will also engage the public and promote education with the aim of engendering a fascination for scientific discovery in younger generations.
"The SKA's scientific advances are across a lot of different astronomical disciplines," says Dr Trott. "So it's very important for bringing together research teams in one science environment to work on understanding the nature of gravity, the extreme parts of our universe like the black holes and neutron stars, and also being able to peer all the way back to the start of the universe. The science goals are big and ambitious and that requires the best international minds.
"The incredible thing about astronomy is that it captures the imagination of people of all different ages, and so from an outreach perspective, understanding our place in the universe and how it has evolved over periods of time are big questions that the SKA can provide the answers to. In schools, universities and other events like Astrofest in Perth, for example, our outreach team can actually excite people about the sciences, which can only have a global beneficial impact in the future."
Source: SKA Organisation
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