By observing the sky at low radio frequencies, LOFAR offers a radically different view from that obtained in visible light. The emissions detected come mainly from relativistic particles moving in magnetic fields, making it possible to trace extreme energetic phenomena: giant jets from supermassive black holes, galaxies undergoing intense star formation, and diffuse structures within galaxy clusters.
A decade of scientific and technological innovation
This major breakthrough is based on more than ten years of observations, algorithmic developments and large-scale data processing.
The Paris Observatory - PSL played a central role in developing the mathematical and algorithmic methods needed to process LOFAR data, particularly to correct distortions caused by the Earth’s ionosphere and to extract weak signals from colossal volumes of data.
"The challenge was primarily mathematical and numerical, and of exceptional magnitude. We had to deepen our theoretical understanding of low-frequency interferometric imaging before we could translate it into robust algorithms capable of processing gigantic volumes of data. This conceptual leap now allows us to achieve a level of fidelity and sensitivity that makes previously unattainable phenomena accessible, from distant galaxies to variable radio signals from stars and, potentially, exoplanets," says Cyril Tasse, a researcher at the Paris Observatory and one of the study’s main contributors.
The processing of 13,000 hours of observation represented a total volume of 18.6 petabytes of data and required more than 20 million hours of computation on high-performance computing infrastructures across Europe.
13.7 million sources and a new perspective on galaxies and clusters
Thanks to its exceptional sensitivity and resolution, LoTSS-DR3 makes it possible to study diverse populations of supermassive black holes at different stages of their evolution, as well as their interaction with their host galaxies and cosmic environment.
‘This immense map of the sky is the result of more than a decade of internationally coordinated observations and analyses. It provides us with an unprecedented statistical view of active galaxies and galaxy clusters, and is already transforming our understanding of the evolution of cosmic structures,’ says Timothy Shimwell, lead author and astronomer at ASTRON and Leiden University.
The survey also reveals rare and elusive objects: merging galaxy clusters, extremely faint supernova remnants, some of the largest and oldest known radio galaxies, destructive stellar bursts (link to type II), as well as transient and variable radio sources. The latter pave the way for the study of exosolar space weather.
Towards the detection of star-exoplanet interactions
Among the discoveries made possible by new analysis methods is the detection of radio emissions consistent with magnetic interactions between certain stars and their exoplanets, analogous to the mechanisms that cause planetary auroras in the Solar System.
‘The radio emissions we are looking for could be direct signatures of magnetic interactions between stars and exoplanets. Their detection would open a new window of observation on exoplanetary magnetospheres and the plasma environment of extrasolar planetary systems,’ explains Philippe Zarka, CNRS research director at the Paris Observatory and specialist in planetary radio emissions.
These results illustrate the potential of radio astronomy archives, which are now being explored with tools capable of tracking large-scale variable and transient phenomena.
A first glimpse of future radio infrastructure
LOFAR is currently evolving into LOFAR2.0, which will double the speed of sky surveys and achieve greater sensitivity. Recent advances in data processing also make it possible to image at even higher resolutions.
‘LoTSS-DR3 is a major milestone. We are entering an era where the joint study of black holes, galaxies, galaxy clusters and variable radio phenomena can be carried out on a very large scale. Future infrastructures, such as LOFAR2.0 and the SKA, will benefit the entire international scientific community,’ concludes Cyril Tasse.
With this unprecedented mapping, LOFAR sets a new benchmark for low-frequency radio astronomy and paves the way for in-depth statistical exploration of the magnetised Universe, from supermassive black holes to star-planet interactions in our galactic neighbourhood.
Reference
The LOFAR Two-metre Sky Survey. VII. Third Data Release by T. W. Shimwell et al., A&A.
DOI: https://doi.org/10.1051/0004-6361/202557749
On the same subject, the article published on the NOVA website (Nederlandse Onderzoekschool voor Astronomie) :
"Largest Ever Radio Sky Survey Maps the Universe in Unprecedented Detail"
| About LOFAR The LOw Frequency ARray (LOFAR) is a revolutionary radio telescope designed and built by ASTRON, the Netherlands Institute for Radio Astronomy. Unlike traditional parabolic antennas, LOFAR consists of thousands of simple antenna elements spread across Europe and connected by fibre optic networks. Data from all the antennas are combined using powerful computers to produce images of the radio sky. The French part of the network is located in Nançay, in the Cher department, within the radio astronomy station of the Paris Observatory (Paris Observatory - PSL / CNRS / University of Orléans). 
© ASTRON
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