The Australian Square Kilometre Array Pathfinder (ASKAP) is a new type of radio telescope designed and built by CSIRO. Our novel application of ‘phased array’ technology, combined with cutting-edge digital signal processing systems makes ASKAP a world-leading radio telescope.
CSIRO's Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope at the Murchison Radio-astronomy Observatory in Western Australia.
CSIRO's Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope at the Murchison Radio-astronomy Observatory in Western Australia.
The ASKAP telescope makes images of radio signals from the sky, allowing astronomers to view the Universe at wavelengths that our eyes cannot see. It is a type of radio telescope known as an ‘interferometer’. This means it uses many antennas acting together as one large telescope. In our case, ASKAP has 36 dish antennas spread out over six kilometres in outback Western Australia.
By combining the signals from 36 smaller dishes, we can make high-resolution images at a fraction of the expense of building an extremely large dish with the same eye for detail.
ASKAP's key feature is its wide field of view, generated by its unique chequerboard Phased Array Feed (PAF) receivers. Together with specialised digital systems, a PAF creates 36 separate (simultaneous) beams on the sky which are mosaicked together into a large single image. This gives ASKAP the ability to rapidly survey large areas of the sky – making it one of the world's fastest survey radio telescopes. ASKAP will help to answer some of the most fundamental questions of 21st century astronomy and astrophysics involving dark matter, dark energy, the nature of gravity, the origins of the first stars, the evolution of galaxies and the properties of magnetic fields in space.
ASKAP can image an area the size of the Southern Cross in a single pointing.
ASKAP can image an area the size of the Southern Cross in a single pointing.
Radio telescopes use specialised cameras called receivers, to detect and amplify faint radio waves from space. One of the challenges facing radio astronomers, was the limited region of the sky that could be seen by conventional receivers at any one time. To solve this challenge, we invented a revolutionary new chequerboard Phased Array Feed receiver, known as a PAF.
These specialised receivers are like an insect’s compound eye on the sky that can look in many directions at once. They house hundreds of detectors that enable astronomers to perform multi-directional searches of the sky simultaneously. They can see an area 40 times larger than a conventional receiver.
The ASKAP ‘PAF’ receiver concept came from CSIRO’s Dr John O’Sullivan. Dr O’Sullivan is also credited with the core technology behind fast Wi-Fi which CSIRO also invented.
Dr John O’Sullivan with an ASKAP PAF prototype.
Dr John O’Sullivan with an ASKAP PAF prototype.
Construction began with a 6-antenna prototype system that made the first PAF image and led to a revised, second-generation design which was deployed on all 36 antennas over several years.
ASKAP is designed to enable a new kind of radio astronomy using rapid mapping technology to conduct all-sky surveys that can be used by astronomers worldwide. Most of the objects detected by the telescope are galaxies outside our own Milky Way galaxy. By cataloguing millions of radio galaxies, we will study the structure and evolution of the universe.
The history of astronomy has involved many detailed studies of small numbers of objects, but to understand how galaxies really work we need to understand their environment and context. This requires detecting and cataloguing millions of sources so that entire populations can be studied statistically.
Galaxies are the building blocks of the Universe. Before ASKAP, about two million galaxies had been detected in the entire 60-year history of radio astronomy at the wavelengths we study. ASKAP’s first all-sky survey has catalogued about three million galaxies, adding significantly to our knowledge in its first year of operation. After five years, we expect ASKAP will discover tens of millions of new galaxies.
ASKAP is located at CSIRO’s Murchison Radio-astronomy Observatory (MRO) in Western Australia (WA). The MRO is about 700 kilometres north of Perth in the Murchison Shire, on the traditional lands of the Wajarri Yamaji. Situated in Mid West WA, the Shire covers an area of 49,500 square kilometers and has a population of 120 people.
This remote location is ideal for radio astronomy as there is minimal interference from Earth-based radio transmissions. In the same way that it is necessary for us to avoid city-lights when we’re looking up at the stars, radio telescopes must avoid other radio communication networks that disrupt the signals being received from space.
The MRO was established in 2009 and is one of the newest observatories in the world. It already hosts three world-class radio telescopes and will be the Australian host site for the Square Kilometre Array telescope, in the 2020s.
At the heart of ASKAP is our custom-designed ‘correlator’, a high-speed digital signal processing system that extracts astronomy signals from this torrent of information.
At the heart of ASKAP is our custom-designed ‘correlator’, a high-speed digital signal processing system that extracts astronomy signals from this torrent of information.
The telescopes at the MRO generate very large volumes of data which are processed on site before being sent to the Pawsey Supercomputing Centre in Perth.
Due to radio quiet requirements, it’s not possible to visit the MRO, apart from specific public open days, but you can take this virtual tour any time.
Two key technologies give ASKAP its capabilities – wide-field PAF receivers and high-speed digital signal processing technology deployed on custom hardware at the MRO, along with custom software running on a supercomputer in Perth. CSIRO engineers developed PAF technology for radio astronomy using a chequerboard array of small receptors and low-noise amplifiers.
ASKAP brings radio astronomy into a data intensive era. The PAF receivers create much more data than a conventional receiver. The telescope’s 36 receivers generate data at the rate of 100 trillion bits per second – more than Australia’s entire internet traffic!
This is too much data to send outside the MRO. To solve this data challenge, we designed a high-speed digital signal processing system, made up of 800 custom-designed circuit boards. This signal processing system is at the heart of ASKAP and it is known as the ‘correlator’. The correlator combines the signals from each antenna and then streams about 40 gigabits of data per second to Perth.
Streaming from the MRO to Perth, ASKAP data travels along high bandwidth (80 Gb/second) optic fibre to the Pawsey Supercomputing Centre that transforms it into astronomical images. ASKAP data is processed on The Pawsey Supercomputing Centre’s ‘Galaxy’ computer. Using special CSIRO-designed software known as ‘ASKAPsoft’, this pipeline produces science-ready images from ASKAP data using advanced image processing techniques.
ASKAP became operational in 2019 and concluded its first pilot surveys in 2020. These early projects were designed to test the telescope’s capabilities and provide example data with which to refine processing strategies.
The ASKAP ‘WALLABY’ science team surveyed three regions around known galaxy clusters, looking specifically for radio emissions from neutral hydrogen gas, which is the fuel for star formation. The map they made of the Hydra cluster shows about 150 sources, compared to the eight discovered in previous images made with other telescopes.
The ASKAP ‘GASKAP’ science team also studies hydrogen gas, but closer to home. One of their first targets was the Small Magellanic Cloud, a very nearby galaxy that orbits our own Milky Way. This image shows more detail than ever before, including filaments of gas moving much faster than expected.
The ASKAP ‘CRAFT’ science team studies sources that only exist for a millisecond – brief flashes of radio waves known as fast radio bursts. These are of great interest for two reasons; their origin is unknown and likely to involve an extremely high-energy object, and their brief nature makes it possible to detect the influence of intergalactic matter on the path from the source to Earth. ASKAP is also one of the few radio telescopes capable of precisely locating the direction from which a fast radio burst came. This capability was used to find “missing matter” that had puzzled cosmologists for years.
In a demonstration of ASKAP’s key capabilities, CSIRO conducted an all-sky survey in 2020 as part of the telescope’s final commissioning phase. The Rapid ASKAP Continuum Survey (RACS) covered the entire sky in just 300 hours of telescope time. RACS is truly ‘rapid’, compared to earlier comparable radio surveys by major world telescopes, which used thousands of hours of telescope time.
With its wide field of view, ASKAP was able to combine 903 images to create the sky map. This is significantly less than the tens of thousands of images needed for earlier surveys.
RACS images are five times more sensitive than what’s been done before, and the images reveal twice the level of detail of any comparable survey.
RACS generated 13.5 exabytes of raw data - which were processed using hardware and software custom-built by CSIRO.
This record-breaking result demonstrates an all-sky survey can be done in weeks instead of years. Over the next few years, ASKAP is expected to conduct even more sensitive surveys in different wavelength bands. Together these 903 images create a new atlas, like a ‘Google-map’ of the Universe.
The Pawsey Supercomputing Centre’s ‘Galaxy’ supercomputer converted the data into 2D radio images containing a total of 70 billion pixels. Each RACS image and associated data occupies about 50 Gbytes; about 50 TBytes for the whole survey.
RACS data is freely available to the public and the astronomy community via the CSIRO data portal CASDA.
This census of the Universe will be used by astronomers around the world to explore the unknown and study everything from star formation to how galaxies and their super-massive black holes evolve and interact. This survey measures millions of galaxies – this is important for statistical investigations into large populations.
RACS is a reference map of the entire sky which we can use for comparison with future surveys. It can also be used to find giant galaxies which are formed due to powerful supermassive black holes accreting and expelling huge jets of material.
Astronomers expect ASKAP’s technology will enable many scientific discoveries about the Universe, for years to come. They are just at the start of the journey using ASKAP’s pioneering technology.
Collaboration with industry has played a crucial role in the development of ASKAP, enabling significant progress on ASKAP's computing architecture, low-noise amplifier design, and geo-exchange cooling systems.
For example, we worked closely with specialist electronics manufacturer Puzzle Precision, based in Newcastle, NSW, who delivered 20,000 printed circuit boards (made from six million individual components) and mechanical assemblies, with very high reliability, required for ASKAP's specialised Phased Array Feed receivers.
ASKAP’s PAFs and on-site digital signal processing hardware were designed by CSIRO and built by Puzzle Precision, with final assembly of the PAFs being done at the Marsfield radio physics laboratory.
ASKAP is one of the precursor instruments to an international project to build the world’s largest radio telescope – the Square Kilometre Array (SKA). SKA telescopes will be built in South Africa and Australia.
ASKAP is carrying out world-class research and providing invaluable science and technology insights for the development of the SKA. In developing ASKAP, the goal was to conduct breakthrough science while simultaneously preparing the astronomy community for the deluge of data that a telescope like the SKA would produce. When ASKAP was being designed, PAF technology had never been used in radio astronomy and pushed the limits of theoretical computational capacity.
ASKAP is demonstrating the high-performance processing required to meet the SKA data challenges. Using the Pawsey Supercomputing Centre , and custom-written software developed by CSIRO, ‘ASKAPsoft’, we produce science-ready datasets of many Terabytes for each observation, served to astronomers through ASKAP’s science data archive, CASDA.