A team of global astronomers has published the most sensitive images of the Universe ever taken at low radio frequencies by using the International Low Frequency Array (LOFAR), according to the South African Radio Astronomy Observatory (SARAO).
LOFAR is one of the unique leading telescopes in the world operated by ASTRON, the Netherlands Institute for Radio Astronomy and co-ordinated by a partnership of nine European countries. These include France, Germany, Ireland, Italy, Latvia, the Netherlands, Poland, Sweden and the UK co-ordinate it. In its ‘high-band’ configuration, LOFAR observes at frequencies of around 150 MHz – between the FM and DAB radio bands, noted the radio observatory body.
Two Rhodes University academics are credited for designing the software that is able to handle the “direction-dependent effects that would otherwise contaminate the images”. They are Dr Cyril Tasse, post-doctoral fellow who, although is currently based in Paris, still remains an honorary research associate of the university, and Professor Oleg Smirnov, Square Kilometre Array chair (SKA) in Radio Astronomy Techniques and Technologies and head of the Radio Astronomy Research Group at the institution.
By repeatedly observing the same regions of sky and combining the data to make a single very-long exposure image, the experts have been able to detect the faint radio glow of stars erupting as supernovae, in tens of thousands of galaxies out to the most distant parts of the Universe.
Said Smirnov: “At LOFAR frequencies, observing the sky is like lying on the bottom of a swimming pool looking up, trying to make out patterns on the ceiling through the choppy water (the “water” being the ionosphere). Some very clever software was required to achieve this.”
Smirnov added that: “We quickly realised the same software can also be used to make MeerKAT images better, and several young researchers from Rhodes University and SARAO also became involved in this project with Dr Tasse.
Some of the academics from the participating countries also shared their views on the major scientific milestone. Professor Philip Best from the University of Edinburgh, UK, who led the deep survey was one of them.
“When we look at the sky with a radio telescope, the brightest objects we see are produced by massive black holes at the centre of galaxies. However, our images are so deep that most of the objects in it are galaxies like our own Milky Way, which emit faint radio waves that trace their on-going star-formation,” he explained
He said the combination of the high sensitivity of LOFAR and the wide area of sky covered by our survey – about 300 times the size of the full moon – has enabled them to detect tens of thousands of galaxies like the Milky Way, far out into the distant Universe.
“The light from these galaxies has been travelling for billions of years to reach the Earth; this means that we see the galaxies as they were billions of years ago, back when they were forming most of their stars,” he added.
Dr Isabella Prandoni of INAF Bologna, Italy also reflected on the achievement. “Star formation is usually enshrouded in dust, which obscures our view when we look with optical telescopes. But radio waves penetrate the dust, so with LOFAR we obtain a complete picture of their star-formation,” she said. The deep LOFAR images have led to a new relation between a galaxy’s radio emission and the rate at which it is forming stars, and a more accurate measurement of the number of new stars being formed in the young Universe, she added.
The remarkable dataset has enabled a wide range of additional scientific studies, ranging from the nature of the spectacular jets of radio emission produced by massive black holes, to that arising from collisions of huge clusters of galaxies. It has also thrown up unexpected results.
For example, by comparing the repeated observations, the researchers searched for objects that change in radio brightness. This resulted in the detection of the red dwarf star CR Draconis.
“CR Draconis shows bursts of radio emission that strongly resemble those from Jupiter, and may be driven by the interaction of the star with a previously unknown planet, or because the star is rotating extremely quickly,” explained Dr Joe Callingham of Leiden University and ASTRON.
LOFAR does not directly produce maps of the sky; instead the signals from more than 70,000 antennas must be combined. To produce these deep pictures, more than 4 petabytes of raw data – equivalent to about a million DVDs – were taken and processed.
“LOFAR is unique in its ability to make high-quality images of the sky at metre-wavelengths,” said Professor Huub Röttgering of Leiden University, who is leading the overall suite of LOFAR surveys. “These deep field images are a testament to its capabilities and a treasure trove for future discoveries,” he added.
“I’m very excited to see what we find when we keep applying the same techniques to MeerKAT, which is an even more sensitive telescope, and will show us even more. The depth and breadth of the window on the Universe that these observations open up is simply unprecedented, so we can expect waves of exciting new results going forward,” concluded Smirnov.