The Fastest Radio Survey of the Southern Sky
Using one of Australia’s most powerful radio telescopes, the CSIRO ASKAP, a new project has completed its survey of the entire southern sky in less than two weeks, breaking the record in timing, in quality of data and resolution. The Rapid ASKAP Continuum Survey (RACS) has now showcased the capabilities available to astronomers for future science studies.
When we look out into the vast, open darkness of space and at the tiny shimmering points of light that seem eternal, the same lights known to the ancients and still looked upon in wonder today, everything still seems to feel ever so far away. Of course, our human brains cannot visualise such distances but its immenseness is felt by all who gaze upon it in bewilderment.
Away from busy city lights, the tiny receiver cells in our eyes can detect about 2000 or so stars, all of which are from our own Milky Way Galaxy - a swirling, massive spiral disc that contains about 100 billion stars. What our visual biological detectors are seeing is light that forms a small portion of the electromagnetic (EM) spectrum, the narrow band of frequencies that make up the optical.
But the spectrum of light or electromagnetic radiation spreads to much higher and much lower wavelengths. Going a little higher in frequency, we enter the ultraviolet range, which gives us a sunburn. Higher still and we start seeing higher energy x-rays and gamma-rays - dangerous forms of energy that can cause harm to our biological cells. Thankfully for us (i.e. all life on Earth), our atmosphere does a fantastic job at blocking out a lot of the high energy stuff out, and we mostly ever come across it at the dentist or other medical purposes.
Heading in the other direction from the optical band, the wavelengths get longer. At first, into infrared - much like the warmth which radiates off a brick wall in the evening, after it has baked in the hot summer Sun all day. Even longer wavelengths also exist - the same kind that our TV and radio signals are broadcast with, radio waves.
Like many of us, Dr. David McConnell remembers looking up at the ever encompassing cosmos as a kid and wondering what could be out there amongst the shimmering lights.
“When I was five, we lived in Alice Springs, and on hot summer evenings, my father and I would lie outside on a rug and look at the stars. He knew their names and would tell me about how far away they are. Those evenings started a life-long fascination with the heavens”.
It’s what drove him to chase his curiosity down the rabbit hole, which would eventually reveal an answer to this very question. Indeed, there are millions and millions of things out there - stars, galaxies, gigantic clouds of gases and more.
These days, Dr. McConnell works for Australia’s national science agency, CSIRO, as a radio astronomer, looking at the radio waves that are generated from astrophysical sources and have made their way across that vast Universe, travelling millions of years to arrive and be detected by a powerful instrument, located in the central outback region of Western Australia.
“Getting into radio astronomy was not a long-term intention. I was studying physics at the University of Tasmania; at that time, the Physics Department was strong in radio astronomy (and still is) and I took the opportunity to work with some radio astronomers doing what seemed to me very interesting work,” he said.
Using the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, a world-leading CSIRO radio instrument, Dr. McConnell and his team have announced the first survey of the entire southern sky in radio frequencies, completed in a record-breaking short time. This has resulted in the astronomical and science communities now having a brand new, detailed atlas of the Universe, analogous to Google Maps - but for objects spread far, deep and wide across southern skies.
One of the most exciting facts about the announcement is the time it took to conduct the sky survey or better stated, the time saved. The project, known as the Rapid ASKAP Continuum Survey (RACS) was able to map 83% of the entire sky (a small portion is too far north to be seen from Australia) in just 12.5 days - an unprecedented speed to observe the enormity of sky that surrounds the Earth, along with the volume of data required to do so. The initial results have today been published in the Publications of the Astronomical Society of Australia.
Previous surveys of similar nature have taken 16 weeks or greater to achieve similar coverage, and have not been able to hit the significant resolution that RACS has delivered on. Amongst the massive amounts of data observed as part of this survey, three million galaxies have been detected, of which about a million are new and have now been catalogued, relative to previous studies.
Historically, mapping the sky (or large portions of it) in radio frequencies has been achieved, with other surveys - in particular, the NRAO VLA Sky Survey (NVSS) which between 1993 - 1996 took 112 days to map the sky (82%) from their northern hemisphere location at 1.4 GHz frequencies (21 cm wavelength) and with an angular resolution of 45 arcseconds. The other notable survey, a little closer to home, was the Sydney University Molonglo Sky Survey (SUMSS) which used an odd-looking radio telescope known as MOST (Molonglo Observational Synthesis Telescope). SUMMS was conducted in 2007, covering the southern sky at 843 MHz.
The difference this time around with RACS is the speed, resolution and sensitivity at which the survey has been conducted. For example, where SUMMS took 12 hours to study roughly a region of sky measuring roughly 4 square degrees, RACS achieves a higher level of sensitivity covering about 30 square degrees, in a mere 15 minutes.
Today’s publication highlights a treasure trove of data that can now be used by the wider astronomical community, adding scientific value for years to come. The RACS data products now contain information by all sorts of radio-emitting characters from the cosmos, including the millions of galaxies spread across billions of light-years, the remnant echoes of ancient supernova detonations, and the bright beacon radio spikes of pulsars, serving as lighthouses shining off at great distances.
The survey itself will become a ‘census’ of different objects which have now been catalogued and become available to the community for further research and analysis, such as galaxy formation models, the interaction between supermassive black holes and what happens to high-speed particles as they zip across the galaxy.
Science Check: The Spectrum in the Sky
The EM spectrum that Earth-based telescopes can see ranges across a number of available ‘windows’ in which the atmosphere allows photons from astrophysical sources to arrive at the surface. These windows are not homogenous in the depths that they reach, with some wavelengths unable to reach sea level, but still come through partially to higher altitudes. It’s for this reason some telescopes reside on top of high mountains or even are built to fly within aeroplanes or on balloons to even greater altitudes.
Radio-frequency bands have long wavelengths, often in the millimetre to kms range and as such can mostly penetrate the opacity of our atmosphere, arriving at telescopes on the surface. Due to the longer wavelengths, telescopes that are attuned to these frequencies are often larger in size, which allows the collection of more radio light. For example, the CSIRO Parkes radio telescope has a diameter of 64 metres - which is an Olympic pool with 7 metres to spare on either side.
The field of radio astronomy itself, when compared to other forms of astronomy, is also still relatively young. Australia has a rich and deep history in the field, with its origins dating back to the emergence of radar technology from World War II. Since then, a number of ‘firsts’ and discoveries have occurred with Australia leading the charge. Instruments like ASKAP, MOST, and the Parkes radio telescope have continually contributed to the field of radio astronomy on a global scale.
There have even been some spin-off technology applications used by billions of people around the world on a daily basis, with origins which can be traced back to the CSIRO offices in Sydney, such as the development of Wi-Fi by radio astronomers who were searching for tiny black holes.
Radio astronomy is described as a sub-field of astronomy focused on studying objects in radio frequencies, such as quasars, pulsars, radio galaxies, Solar system bodies (like the Sun and Jupiter), supernovae remnants, active galactic nuclei (AGN), supermassive black holes, and the cosmic microwave background.
To complete this research, Dr McConnell and his team used ASKAP, one of the CSIRO’s most recently developed radio instruments, made up of 36 x 12-metre dish antennas spread across the flatlands of the Murchison Radio-astronomy Observatory (MRO).
All of ASKAP’s antennas act as a single telescope, covering a large portion of the sky at any given time - which allows quick survey timeframes to be combined with a high level of sensitivity. This is very ideal for big-sky-coverage projects like RACS.
“For the first time, ASKAP has flexed its full muscles, building a map of the Universe in greater detail than ever before, and at record speed. We expect to find tens of millions of new galaxies in future surveys,” Dr McConnell said.
Each of the 12m ASKAP dishes is fitted with a unique, specialised receiver known as a ‘phased array feed’ – custom technology developed by CSIRO, which allows each antenna to scan the sky using 36 separate and simultaneous beams. When combining this data from all dishes, a massive 30 square degrees of the sky (about the same area covered by the Southern Cross constellation) can be surveyed quickly, accurately, and with unprecedented resolution. This is one of the advantages of ASKAP, whose field of view registers about 30 times larger than other radio telescopes.
CSIRO Chief Executive Dr. Larry Marshall said ASKAP brought together world-class infrastructure with scientific and engineering expertise to unlock the deepest secrets of the Universe.
“ASKAP is applying the very latest in science and technology to age-old questions about the mysteries of the Universe and equipping astronomers around the world with new breakthroughs to solve their challenges,” Dr. Marshall said.
The instrument is located at the MRO, (central Western Australia) in the special government-dedicated radio quiet zone, a region where no mobile phones work and no transmissions of other radio sources are allowed. The strict rules are applied to ensure that even the most feeble of signals emanating from deep space are received by the sensitive detectors.
ASKAP’s spread of 36 dishes across the region also gives it several points of differentiation amongst other radio telescopes and arrays. The large baseline between the antennas allows an even higher degree of resolution. This also allows ASKAP to accurately localise and pinpoint the location of radio sources to a higher degree than any other radio telescope in the world, as recently demonstrated by the localisation of fast radio bursts in distant galaxies.
A virtual tour of ASKAP has also been produced, allowing the public to experience a 3D panoramic view of the observatory with some of the discoveries made in radio light.
Rapid ASKAP Continuum Survey (RACS)
The origins of RACS can be traced to the development and testing of ASKAP. An instrument as large, complex and powerful as the array would first need to be understood properly, in terms of its capabilities, its drawbacks and how far the innovation surrounding engineering, software development, data processing and more can be pushed.
From this, RACS was born - designed to test ASKAP ahead of all major surveys, showcasing how the telescope can be used in short amounts of time to produce high volumes of useful data for a range of astronomy questions.
In a nutshell, RACS is an all-sky survey designed to test using all 36 dishes together to produce results at high speed and high precision.
Whilst RACS is an international collaboration of scientists, from within Australia several institutions are involved in the release of this paper, including the CSIRO, the International Centre for Radio Astronomy Research (ICRAR), the University of Sydney, University of Technology Sydney, Western Sydney University, and the Australian National University.
The main objective of RACS is to provide the first version of an almost all-sky survey using ASKAP, which can be used to further calibrate deep-sky surveys of the future which are planning on using the telescope. Additionally, the results from RACS will provide the astronomical community with a powerful new asset of the sky, supplying images captured in radio frequencies.
RACS uses all 36 antennas across ASKAP, with varying baselines that stretch as small as 22m and extend out to over 6km. The deep resolution achieved is much higher than all previous surveys (by several magnitudes) and measured at 15 arcseconds. Each image captured by RACS runs for an integration time of 15 minutes, and to cover the entire sky (excluding the out of reach northern latitudes), RACS generated 903 image tiles.
The observations for this project were made at 888 MHz, which represent a wavelength of approximately 34 cm. This now also helps fill in the gaps a little more across radio observations of other surveys and with other instruments - acting as a bridge between low-frequency surveys by GLEAM and TGSS and higher frequency surveys like NVSS.
And whilst the details observed by RACS resemble a starry sky - reminding us of the optical equivalent - the points of light are actually millions of galaxies seen in radio wavelengths that are at great distances from the Earth, residing far from the Milky Way Galaxy. The survey thus presents a beautiful global and deep view of the Universe at large.
“It’s been very exciting to see the images rolling out of ASKAP, all the way from the Moon (yes, it intruded on two of our fields that were later observed) to the most distant-known radio galaxy, easily detected in RACS,” said Dr. McConnell.
“The RACS images include many amazing objects, and it is hard to settle on a particular favourite. I am struck by the beauty of some of the supernova remnants, the great bubbles and shockwaves leftover from exploding stars”.
“The remnant known as Puppis-A is a favourite. It is quite close, being “only” 7,000 light-years away, and appears as a large shell with many delicate arcs showing the location of shocks travelling through the interstellar medium”.
“ASKAP is also a vastly complicated instrument” continued Dr. McConnell. “Succeeding with the RACS project has required understanding and learning how it should be operated to produce the best images,”
“Indeed, one of the aims of the RACS project was to test the telescope’s abilities and develop the best techniques for its operation. This complexity extends to the software used to form the images. That software has had to deal with features of the telescope that are quite novel and incompletely tested until used on RACS.
Each of the images generated by RACS a gigabyte in size, with several images used for each field. To allow such huge data requirements to functionally work from a number of different perspectives (data engineering, storage, processing, transmission, etc.) - dedicated resources were required to be brought in.
More Data than Australia's Internet Traffic
RACS (with reference to ASKAP) is a big data-hungry project that draws on an extreme amount of detail, at high resolution over a large field of view. This in turn means it demands powerful high-performance computing to process the data that runs through its pipelines.
CSIRO has dedicated its own supercomputer for processing ASKAP data.
As part of RACS, 13.5 exabytes of raw data was generated by ASKAP and processed using hardware that was custom-built by CSIRO for this purpose. For comparison, an exabyte of data is equivalent to the entire global internet traffic in March 2010 was 21 exabytes of data. To assist in supporting this, the Pawsey Supercomputing Centre (located in Perth) played a vital role in the project.
The Pawsey Supercomputing Centre is a joint effort program between the CSIRO, Curtin University, Murdoch University, The University of Western Australia and Edith Cowan University and was developed to provide high-performance computing capabilities for science research projects.
Pawsey Executive Director Mark Stickells said the supercomputing capability was a key part of ASKAP’s design.
“The Pawsey Supercomputing Centre has worked closely with CSIRO and the ASKAP team since our inception and we are proud to provide essential infrastructure that is supporting science delivering great impact,” Mr Stickells said.
The Pawsey Supercomputing Centre’s ‘Galaxy’ supercomputer converted the data from RACS into 2D radio images containing a total of 70 billion pixels. The final 903 images and supporting information amount to 26 terabytes of data. In general, ASKAP generates more raw data at a faster rate than the entire internet traffic of Australia’s population in 2020.
Additionally, the in-house image processing software had to be developed for projects like RACS, which set out the path to utilise high-performance computers that could reduce the massive amounts of data into images and catalogues. Known as ASKAPsoft the software takes the raw data from the telescope and uses it to reconstruct an image that is ready for usage by scientists. This all occurs on the supercomputer ‘Galaxy’, hosted by the Pawsey Centre.
What's next for ASKAP?
The ASKAP project is currently developing, testing and learning answers to the many complex questions that are required to be resolved, as part of the development of the SKA - such as how even more data can be processed, how to utilise machine learning to automate target identification, and how to generate renewable energy to power the facility without introducing radio interference.
ASKAP itself is a pathfinder project for the more ambitious Square Kilometre Array (SKA) telescope - one of science’s mega-projects, being constructed from next year through to the end of the decade. Once completed, the SKA will be the largest scientific instrument in the world, spread across two continents (South Africa and Australia), acting as the world’s biggest ‘radio eye’ with the ability to peer to some of the earliest moments in the Universe’s history.
Minister for Industry, Science and Technology, Karen Andrews said ASKAP is another outstanding example of Australia’s world-leading radio astronomy capability.
“ASKAP is a major technological development that puts our scientists, engineers and industry in the driver’s seat to lead deep space discovery for the next generation. This new survey proves that we are ready to make a giant leap forward in the field of radio astronomy,” Minister Andrews said.
With RACS now proving that ASKAP is a powerful new-gen tool for the astronomical science community, future surveys will soon start to be awarded to research projects, to turn all 36 dishes towards their next target in the Universe. The ability for these future projects to scan the sky with this level of detail in just a few weeks, then re-map the same sky in a range of different frequencies within the same month is going to open up many exciting possibilities to learn about the Universe, answering questions about transient events and how the Universe changes on the short term.
Currently, there are eight international teams working with the CSIRO to build future surveys that address questions like how the galaxies have changed over time, what role do magnetic fields play in galactic evolution, what is special about how gas moves in nearby galaxies, and what are the known sources of transient events like fast radio bursts.
As Dr. McConnell wraps up, he outlines how RACS is going to be used as both a target selection tool in the future, and a snapshot to measure against for future surveys.
“RACS is the first complete survey made with ASKAP, and it is a demonstration to the teams that the telescope works. The RACS images will be used by some projects as a reference against which to compare future images in the search for changes in the radio sky”
“Other projects will use RACS as a finding chart to target objects for different kinds of studies, for example, to study the spectral or polarisation properties”.
In roughly 60 years, Australian researchers and scientists have been at the forefront of radiophysics and astronomy, helping pave the way for future generations of scientists which have returned value back to society.
Our world-class facilities and dark sky capabilities (even in the radio sense) have allowed us to develop instruments like ASKAP, which in turn has allowed us to peer deeper into the Universe, including at higher resolutions. We can now see things that we only once theorised about in textbooks.
The future mega-science project, the Square Kilometre Array is going to really re-shape our understanding of the Universe, and its projects like RACS and other future ASKAP surveys that will help define what that generation of instruments will be capable of achieving.
Astronomers like Dr. McConnell and his team still look up at the night sky in wonder, considering all the enormity and scale of what lies beyond our atmosphere. Only now, we have an instrument equipped with 36 eyes that can take snapshots at small time intervals, helping us better define what we are looking at and how it is changing over time.
There are still many scientific questions that need resolving – which in doing so will generate new questions to be asked which eventually are resolved, then generate their own questions and so forth. Such is the wonderful ebbing flow of science and discovery over time.
Now having the capabilities of ASKAP and projects like RACS means the technology has taken a leap ahead, throwing massive amounts of data at us to learn from – a garden from which we can pick low-hanging discoveries from, or take a deep dive into the great unknown.
Strap yourselves in, the fun stuff is only just about to begin.
The images and catalogues from the survey will be made publicly available through the CSIRO Data Access Portal and hosted at Pawsey. This data will be available to anyone around the world.
We acknowledge the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site.
The paper is now available in the journal, PASA