The Square Kilometre Array (SKA)

The Square Kilometre Array (SKA) is a multi-purpose radio telescope, covering the frequency range from 50 MHz to 20 GHz that will play a major role in answering key questions in modern astrophysics and cosmology. It will be one of a small number of cornerstone observatories across the electromagnetic spectrum that will provide astrophysicists and cosmologists with a transformational view of the Universe.

Timeline

SKA science layout
Artist's impression of the layout of the SKA telescopes. Credit: SKA Organisation/Swinburne Astronomy Productions.

The SKA will have collecting area approaching one million square metres and be capable of observing across a wide frequency range. Its construction is thus a major undertaking and will be implemented in phases to allow significant observations to be made before construction is completed.

The international project has adopted the following terminology to describe this phased approach:

  • Phase 1 is the initial deployment to begin in 2018 and integrating the MeerKAT and ASKAP precursor telescopes;
  • Phase 2 will become fully operational in the mid-2020s, increasing both the sensitivity and resolution by over an order of magnitude. For the latest information see the SKA Timeline on the SKA Telescope website.

Key science

The international community has developed a detailed and compelling science case for the SKA, as described in detail in the book "Advancing Astrophysics with the Square Kilometre Array". The JBCA group has been a major contributor to it with 45 of the 135 papers having Manchester authors and 12 of those have a lead author from the JBCA. You can download a copy of the book from the SKA Telescope website

The core of the science case is eight key topics; each topic represents an unanswered question in fundamental physics or astrophysics, is science either unique to the SKA or for which the SKA plays a key role, and is something which can excite the broader community.

The eight topics are as follows: 

  • Epoch of Reionization and the Dark Ages: Investigating the formation of the first structures, as the Universe made the transition from largely neutral to its largely ionized state today.
  • Fundamental Physics with Pulsars: Identifying a set of pulsars on which to conduct high precision timing measurements. The gravitational physics that can be extracted from this data can be used to probe the nature of space and time.
  • HI and Galaxy Evolution: Probing the properties of galaxies, their assembly and their evolution by carrying out all-sky surveys of continuum emission and of HI to a redshift z ~ 2.
  • Cosmology: The SKA will deliver precision cosmology and probe the foundations of the standard model, including dark energy, and open the door to new discoveries on large-scale features of the Universe.
  • Cosmic Magnetism: Magnetic fields are an essential part of many astrophysical phenomena, but fundamental questions remain about their evolution, structure, and origin. The goal of this project is to trace magnetic field evolution and structure across cosmic time.
  • Astrobiology/Cradle of Life: Probing the full range of astrobiology, from the formation of prebiotic molecules in the interstellar medium to the emergence of technological civilisations on habitable planets.
  • Continuum SurveysThe SKA’s angular resolution and survey speed capability will mean that continuum surveys will be more detailed than ever before. These surveys will allow new studies into galaxy and galaxy cluster physics.
  • Radio Transients: The SKA will be able to survey the sky at a rate faster than any survey telescope that has ever existed and so will be able to discover transient phenomena with time scales from below even one nanosecond through to several years. These will include Gamma Ray Burst, supernovae and Fast Radio Bursts but will also allow an "Exploration of the Unknown".

The SKA has been conceived as a observational facility that will test fundamental physical laws and transform our current picture of the Universe. However, the scientific challenges outlined above are today's problems; will they still be the outstanding problems that will confront astronomers in the period 2020-2050 and beyond, when the SKA will be in its most productive years?

More about the JBCA scientific involvement with the SKA can be found in the JBCA science activity section.

Sites

SKA dishes on the South African SKA site
SKA-Mid. Artist impression of the SKA dishes on the South African SKA site, with MeerKAT dishes in the background. Credit: SKA Organisation.

The SKA will be co-hosted at the South Africa's Karoo region (as a core site) and Western Australia's Murchison region (MRO). Different elements of the telescope will be deployed at the two different sites, with SKA-Low and SKA-Survey located at the MRO and SKA-Mid at the Karoo.

SKA-Mid

The SKA-Mid will comprise 15-m offset Gregorian dishes equipped with wide-band single pixel feeds and will be incorporated with the MeerKAT telescope, giving a total of 197 antennas. The array configuration will extend to a radius of 100km from a highly filled inner core of antennas. This implementation of the mid-band SKA represents a low risk approach to cover the 350 MHz to 15 GHz frequency range. The highly filled core is necessary for experiments such as the pulsar surveys, while the long baselines provide the angular resolution required for cosmology.

Low frequency antennas in Australia
SKA-Low. An artist impression of the low frequency antennas in Australia with the ASKAP telescope in the background. Credit: SKA Organisation.

SKA-Low

The SKA-Low telescope will comprise 131,000 individual element configured as an aperture array. In an aperture array a beam is formed and steered by combining all the received signals from a 'station' of 256 elements after appropriate time delays have been introduced to align the phases of the signals coming from a particular direction. By simultaneously using different sets of delays, this can be repeated many times to create many independent beams, yielding very large total Field of Views. The number of useful beams produced, or total Field of View, is essentially limited by signal processing, data communications and computing capacity. Aperture arrays can readily operate at low frequencies and can provide large effective areas. Arrays using substantial digital processing systems are inherently very flexible since the system can 'trade' Field of View and bandwidth and hence provide an instrument that can be matched to that required by the experiment.

SKA technical work at The University of Manchester

The SKA project is now in the process of conducting the detailed design work for the telescope and various international consortia have been formed to carry out this technical work. The University of Manchester is a member of five of these consortia and in the case of SaDT is also the lead institute.

Signal and Data Transport Consortium (SaDT)

Signal and data transport is the backbone of the SKA telescope. The Signal and Data Transport (SADT) consortium is responsible for the design of three data transport networks. These are:

  • a network to take astronomical data from the antennas to the correlator and then on to the High Performance Computer (HPC) facility;
  • a network to distribute clock and synchronization signals from a central ensemble of very accurate clocks (probably hydrogen masers) out to each antenna;
  • a non-science data network (NSDN) to allow distribution of the monitoring, control and auxiliary networking data throughout the whole SKA system

Each of these has its own individual challenges and we will also be working to find an optimal solution for combination of the three networks taken as a whole.

The volume of telescope data to be transported is vast. Although the final data rate depends on features of the overall system still to be determined, current estimates put the data rate as approximately 23 Tb/s (terabits per second) from the antennas to the correlator (provided by CSP) and then another 14 Tb/s from the correlator to the HPC (provided by SDP). This is equivalent to 12,000 PB/month (petabytes per month); for comparison the World's total IP traffic in 2011 was 27,000 PB/month. In addition to the volume, we have to transport the data for considerable distances eg in Australia the correlator is approx 800km from the HPC centre in Perth.

The Synchronisation and Timing (SAT) provides frequency and clock signals from a central clock ensemble to all elements of the system to maintain phase information to the required accuracy for all receptors, and timing signals for data identification and time critical activities at the receptors, the CSP and SDP. To maintain phase coherence across the array requires short-term timing precisions of around 1pico-sec, while for the requirements for pulsar timing experiments require 10 nano-secs accuracy over 10 year periods.

The auxilliary “campus style” data network consists of an access layer, distribution layer and a Multi-protocol Label Switching Core network which has a footprint across the entire observatory site. It is designed as converged network to carry multiple services that support the operation of the telescopes. It is primarily responsible for transporting monitoring and control information between the Telescope Manager and the monitoring and control interfaces of all sub-systems, but it also transports general data communication services such as Internet connectivity, Voice and Infrastructure services. It must have high availability, good security and connect all the SKA trusted offices, including locations off-site.

The University of Manchester is the lead organisation for the SaDT Consortium, with the group headed by Prof Keith Grainge. We have collaborators in AARNet (Australia), CSIRO (Australia),GÉANT (EU), IT (Portugal), JIVE (The Netherlands), NCRA-TIFR (India), NMMU (South Africa), the National Physical Labortary (UK), SANReN (South Africa), SKA-SA (South Africa), Tata Consulting (India), Tsinghua University/ Peking University (China), University of Granada (Spain) and the University of Western Australia (Australia).

Non-Imaging Processing (NIP)

Within the Central Signal Processing (CSP) and Science Data Processing (SDP) consortia the University of Manchester leads the Non-Imagining Processing (NIP) sub-tasks which are required for Pulsar searches and Pulsar timing experiments. This work is led by Prof Benjamin Stappers. The computational load for this task is daunting since a huge parameter space must be searched over in order to find pulsar candidates in the data stream.

Data reduction pipelines within SDP

The Manchester group leads the Imaging Pipeline (PIP.IMG) and Non-Imaging (PIP.NIP) work packages within the SDP Consortium. This work package is responsible for providing details of software functionality associated with the imaging and non-imaging pipelines including:

  • algorithmic descriptions
  • implementation details
  • prototyping work
  • image fidelity analysis
  • pulsar and fast transient search candidate identification
  • precision pulsar timing analysis

The PIP.IMG team includes ~20 members from 6 countries and is led by Dr Anna Scaife, while the PIP.NIP team includes ~8 members from 3 countries led by Prof Ben Stappers.

Low Frequency Aperture Array (LFAA) and Mid Frequency Aperture Array (MFAA)

Octagonal Ring Antenna
Octagonal Ring Antenna (ORA).
ORA measurement.

Within the LFAA and MFAA consortia the University of Manchester is leading work on a novel type of receiver element, an Octagonal Ring Antenna (ORA). This work is led by Prof Tony Brown in the School of Electrical and Electronic Engineering. This technology is a planar array of antennas which can be easily fabricated at low cost while maintaining excellent performance.

The ORA's properties include:
  • A simple planer structure based on low cost manufacturing techniques
  • Low and stable cross polarization over broad bandwidth and wide scan angle
  • Wide scan angle with a stable scan pattern
  • Feed connection flexibility, can be fed with a differential and single-ended LNA

Office for the SKA Organisation

The Office for the SKA Organisation is responsible for coordinating the global activities of the SKA project. This includes engineering, science, site evaluation, operations and public outreach. It is located at the Jodrell Bank Observatory, hosted by the University of Manchester. The history runs from the first discussions in 1993, to the establishment of the Project Office at the Jodrell Bank Centre for Astrophysics in 2008, and the SKA organisation in 2011.

Did you know?

The SKA central computer will have the processing power of about one hundred million PCs.

The new Square Kilometre Array (SKA) science animation showing the five key science questions that the SKA will answer.

Associate Director of Jodrell Bank Observatory Tim O'Brien gives an inspiring presentation on why we should care about the Square Kilometre Array and what it represents.

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