The radio telescope LOFAR, with a major contribution from Leiden Observatory, has produced the most detailed radio map of the Universe ever made. Never before have so many cosmic radio sources been captured in a single survey: 13.7 million.
The survey also provides the most complete census so far of actively growing supermassive black holes. This new data release, known as LoTSS-DR3, marks an important milestone for radio astronomy and for scientific collaboration across Europe. The results are published today in the journal Astronomy & Astrophysics.
Revealing invisible objects and events
Observing the Universe at low radio frequencies reveals a very different picture from what we see in visible light. Much of the detected radiation comes from particles moving at nearly the speed of light through magnetic fields. This allows astronomers to trace energetic events such as powerful jets from supermassive black holes and galaxies undergoing intense bursts of star formation over cosmic timescales.
Because the survey mapped almost the entire northern sky with high sensitivity and sharp resolution, it has also uncovered rare and elusive objects. These include merging clusters of galaxies, faint supernova remnants, and stars that are erupting or interacting with each other. The data set opens the door to hundreds of new studies and offers fresh insight into how cosmic structures form and evolve, how particles are accelerated to extreme energies, and how magnetic fields behave across vast distances.
A decade of international collaboration
The survey was carried out within the LOFAR European Research Infrastructure Consortium (LOFAR ERIC), bringing together expertise from the Netherlands, Germany, France, the United Kingdom, Poland, Italy, Sweden, Ireland, Latvia and Bulgaria. LOFAR consists of 38 stations in the Netherlands and 14 international stations across Europe, with the most distant stations nearly 2,000 kilometres apart. This wide distribution makes LOFAR one of the largest and most sensitive radio telescopes in the world, with very high resolution.
'This data release is the result of more than ten years of observations, large-scale data processing and scientific analysis by an international research team,' says lead author Timothy Shimwell from the Leiden Observatory and ASTRON.
About LOFAR-ERIC
The LOw Frequency ARray (LOFAR) was designed and built by ASTRON, the Netherlands Institute for Radio Astronomy. Unlike traditional dish telescopes, LOFAR uses thousands of simple antenna elements spread across Europe and connected by fibre-optic networks. Powerful computers combine the signals from all these antennas to create detailed images of the radio sky.
LOFAR is managed by LOFAR ERIC, a consortium of institutions from eight countries. It is an example of international scientific cooperation, pooling facilities, computing power, and expertise across borders.
The discoveries: black holes, supernovae and exoplanets
The survey has delivered robust measurements of millions of black holes. 'This is a major step forward because we can now study an entire population of black holes,' says Leiden co-author Huub Röttgering. 'A key question is how and where black holes grow as the Universe expands and ages.'
'How and where do black holes grow as the Universe expands and ages?'
'Using statistics, we can now show how particle acceleration and the strengthening of magnetic fields are driven by shocks and turbulence across millions of light-years,' adds co-author Andrea Botteon of INAF in Bologna, Italy.
The team is carefully searching the data for rare astrophysical phenomena. They have identified transient and variable radio sources, previously unknown supernova remnants, some of the largest and oldest known radio galaxies, and radio emission that may come from interactions between exoplanets and their host stars.
Overcoming technical challenges
'The technical challenge was enormous,' says co-author Reinout van Weeren, also from the Leiden Observatory. 'The biggest difficulty was the disruptive effect of the ionosphere, a high layer of the atmosphere that also causes the northern lights. We had to develop new algorithms to filter out these disturbances and produce high-quality radio images. Additionally, it was crucial to make these algorithms highly efficient, so that we could compile this survey from the 18.6 petabyte dataset collected over 13,000 hours of LOFAR observations.'
The world's largest radio map - LoTTS Data Release 3
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'Not an endpoint, but an important milestone'
LOFAR is now being upgraded to LOFAR2.0, which will double the observing speed. Recent advances in data processing also make it possible to produce images with much higher resolution, opening the way to even more detailed studies.
'LoTSS-DR3 is not an endpoint, but an important milestone,' says Wendy Williams, scientist at the Square Kilometre Array Observatory (SKAO). 'With new facilities such as LOFAR2.0, we can map the radio Universe with even greater sensitivity and resolution.'
Scientific paper
The LOFAR Two-metre Sky Survey VII. Third Data Release, 2026, T.W. Shimwell et al., Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202557749
This press release originally appeared on astronomie.nl
About NOVA
The Netherlands Research School for Astronomy (NOVA) is a partnership between the astronomy institutes of the universities of Amsterdam, Groningen, Leiden and Nijmegen. NOVA's mission is to carry out leading astronomical research, train young astronomers at the highest international level, and share new discoveries with society. NOVA laboratories specialise in building advanced optical, infrared and submillimetre instruments for the world's largest telescopes.
