Radio Astronomy: Square Kilometre Array

The MeerKAT telescope, situated in the Northern Cape, South Africa, is thefirst major step to the future of radio astronomy and serves as the predecessor to the Square Kilometre Array (SKA). MeerKAT, being one of the mostpowerful radio telescopes in the world, reveals the capabilities of modernastronomical instruments as well as showing that South Africa is capable ofimmense feats of engineering and can be a leading contributor for the future ofscience and innovation.

Engineering aspects

MeerKAT consists of 64 radio antennae, each of which have a 13.5m primaryreflector (consisting of 40 aluminium panels each) and a 3.8m sub-reflector. Thedishes are constructed using an Offset Gregorian optical layout which focuses the light from one direction via the primary reflector onto the sub-reflector which then focuses the light into the receiver, reducing the total areaof each dish that becomes blocked by the receiver/reflector and support struts.Each antenna is approximately 19.5m high and weighs 42 tons. The antennae are arranged such that 48 of them are concentrated in the core, approximately 1km in diameter, and the remaining 16 lying further away with a maximum baseline of 8km. In addition, 170km of fibre-optic cables have been placedunderground for the transfer of data.

Data Challenges

Since the first stages of KAT-7, significantly more resources have been needed to store and process the increasing amount of data being received as well as power the project. This is becoming a much larger problem during the operation of MeerKAT and as the opening of SKA draws nearer.1A Pathfinder for the SKA, the Australian SKA Pathfinder (ASKAP) wasexpected to have the following data and power requirements: bandwidth of10Tb/s from antennas to correlator and 40Gb/s from correlator to processor, 750Tflop/s processing power, 1MW on site and 10MW to power the processor,and a maximum of 70PB/yr to store all the data received and processed. In addition it would take approximately 8 hours to write 12 hours of data to diskat 10Gb/s. The combined data volume for all the Pathfinders is expected tobe 8PB, and the final SKA project will far exceed this.

The main method for handling the inflow of data is the development of advancedcomputer algorithms to efficiently process and store the data. The Institute forData Intensive Astronomy (IDIA), started by the University of Cape Town,University of the Western Cape and the North-West University, aims to bringtogether data and computer scientists to manage the vast amount of data fromMeerKAT and the future SKA project.

Science Projects for MeerKAT

Following the opening of Meerkat in July 2018, many projects have been as-signed observation time for various purposes. Figure 2 shows the first imagetaken of the galactic centre with the fully functioning MeerKAT telescope. An impressive feature of this image is the immense detail that can be seen as well as being capable of seeing Planetary Nebulae and Supernova remnants with such clarity.

There are a total of 10 projects which have been allocated observation time for MeerKAT, 3 of which are South Africa led projects: LADUMA (Looking at the Distant Universe with the MeerKAT Array)-looking at neu-tral hydrogen (21cm emission line) in the early universe led by Dr Sarah Blyth,MIGHTEE (MeerKAT International GigaHertz Tiered Extragalactic Explo-ration Survey)-looking at early radio galaxies led by Dr Kurt van der Heyden,and ThunderKAT (The Hunt for Dynamic and Explosive Radio Transientswith MeerKAT)-observing gamma ray bursts, novae and supernovae led by Pro-fessor Patrick Woudt.

South African involvement in SKA

The entire array will be split up into two countries, Australia and South Africa.At present, South Africa will host 200 dishes, including those of MeerKAT in the Phase 1 of the SKA construction and possibly another 250 Mid Frequency Aperture Array stations after Phase 2 of the construction, while Australia will host up to 1,000,000 Low Frequency Aperture Array Antennae in addition tothe ASKAP dishes.

South Africa was chosen to be a major part of the project due to high quality infrastructure in conjunction with its cheaper cost for international investors due to lower exchange rate. South Africa also has a large portion of its land completely uninhabited allowing a radio-free region to be established relatively easily. Also, the level of higher education allows for highly skilled astronomers, computer scientists an data scientists to become involved, which also played arole in the decision of the SKA site.

Further information

Due to the data challenges, non-conventional methods of data storage needed tobe implemented. In particular, data is stored on tapes (similar to old cassettes)instead of in the conventional digital format (disks or on hard drives). This isdue to the ease of data transfer and storage of tapes as well as a low risk of data being lost by damage to the physical storage device. These tapes incredibly havea 300Gb/s transfer speed and a total of 6Tb of space on each, which surprisingly only stores data for 15 minutes of observation (highlighting the challenges facing data scientists and computer scientists in the SKA project).

11 February 2020
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