Sky survey reveals ‘hundreds of thousands’ of undetected galaxies

Astronomers from UCD in group that used telescopes at Birr, Co Offaly and abroad

A sky survey conducted by 200 astronomers has revealed the presence of hundreds of thousands of previously undetected galaxies and has shed light on the physics of black holes.

The team of astronomers from 18 countries, including researchers from University College Dublin (UCD), have released the first phase of their survey.

The work is of such significance a special issue of the scientific journal Astronomy & Astrophysics has been published dedicated to the first 26 research papers based on its results.

The survey was made possible due to the "unprecedented sensitivity" achieved using the low frequency array (LOFAR) telescope at Birr Castle in Co Offaly, according to Prof John Quinn of UCD School of Physics, who contributed to it with PhD researcher Sean Mooney.


Radio astronomy reveals processes in the universe that cannot be seen with optical instruments, said Prof Quinn.

“LOFAR observed a quarter of the northern hemisphere at low radio frequencies. At this point, approximately 10 per cent of that data is now being made public,” he said. “It maps 300,000 sources, almost all of which are galaxies in the distant universe; their radio signals have travelled billions of light years before reaching Earth.”

The UCD duo are lead authors on one of the papers published, and contributed to several others. Their paper is focused on the jets from supermassive black holes that are pointed towards the Earth. A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing, not even particles and electromagnetic radiation such as light, can escape from inside it.

Principal investigator Prof Huub Röttgering of Leiden University said: "If we take a radio telescope and we look up at the sky, we see mainly emission from the immediate environment of massive black holes. With LOFAR we hope to answer the fascinating question: where do those black holes come from? What we do know is that black holes are pretty messy eaters. When gas falls onto them they emit jets of material that can be seen at radio wavelengths."

Prof Quinn said the survey provides “an unprecedented view of galaxies with supermassive black holes at their centres, and how they evolve. The sensitivity and resolution . . . is unparalleled at low frequencies, and the technological advancements required to make this possible are relatively recent.”

Creating low-frequency radio sky maps requires significant computational resources. Much of the analysis has been done at SURFsara data centre in Amsterdam, which hosts a vast amount of LOFAR data – more than 20,000 terabytes.

"It is the largest astronomical data collection in the world. Processing the enormous data sets is a huge challenge for scientists. What normally would have taken centuries on a regular computer was processed in less than one year,"said Dr Raymond Oonk of SURFsara.

Machine learning algorithms were used to automate parts of the analysis, with some of this work being done at UCD on powerful computing clusters.

The international LOFAR telescope system consists of a European network of radio antennas, connected by a high-speed fibre-optic network spanning seven countries. LOFAR was designed, built and is now operated by the Netherlands Institute for Radio Astronomy (ASTRON).

The team aims to make sensitive high-resolution images of the whole northern sky, which will reveal 15 million radio sources in total.

"This sky map will be a wonderful scientific legacy for the future. It is a testimony to the designers of LOFAR that this telescope performs so well", said ASTRON director Carole Jackson. "Just imagine some of the discoveries we may make along the way. I certainly look forward to it."

The Irish station, I-LOFAR was installed in 2017 with funding from Science Foundation Ireland, Enterprise Ireland, the Department of Business, Enterprise, and Innovation.

Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times