LOFAR produces its sharpest, deepest low-frequency radio image, revealing 63,000 sources

An international team led by Leiden University has made the sharpest and most sensitive low-frequency radio image of the sky to date, using the Low Frequency Array (LOFAR). The image covers the ELAIS-N1 field, a region of the northern sky about 25 times the area of the full moon, and contains almost 63,000 radio sources. The work has been accepted by Astronomy & Astrophysics and is available as an arXiv preprint.

A deeper, sharper view of a familiar field

ELAIS-N1 is a well-studied patch of sky containing many faint, distant galaxies. The new image is 20 times sharper than the previous most sensitive LOFAR image of the same area. According to the team, its resolution is fine enough to pick out a coin from roughly 10 kilometres away. At this scale the full image holds 8 billion pixels.

The observations amounted to 200 hours of data, totalling 400 terabytes. The sources include active galactic nuclei and star-forming galaxies.

Making the processing affordable

Much of the achievement is computational. High-resolution imaging of this kind with a low-frequency radio telescope was, for years, effectively out of reach because of the volume of data. Improved calibration and data-reduction methods developed by the team and collaborators have cut the processing cost by more than a factor of 10 in recent years.

Jurjen de Jong, a postdoctoral researcher at Leiden Observatory and ASTRON who led the study, reports that the complete data set could be processed in a few months on Spider, a high-performance data-processing platform hosted at SURF in the Netherlands.

What the sharper view reveals

Active galactic nuclei are among the dominant populations in the image. These are the luminous cores of galaxies powered by matter falling onto a supermassive black hole, and they can launch powerful jet-like outflows. LOFAR is particularly sensitive to the faint, extended radio emission associated with them.

In lower-resolution images, distant galaxies and jets appear as featureless blobs. It is then difficult to tell whether a source is made up of several galaxies or components, or whether the radio emission comes from a jet or from star formation. In the new data these components and emission sources can be separated more readily, and large jets can be traced in detail. Co-author Reinout van Weeren, associate professor at Leiden Observatory, says the image offers a new way to study how jets interact with their surroundings and evolve over cosmic time.

The second major population is small star-forming galaxies. Radio waves pass through the dust that obscures star formation at optical and infrared wavelengths, so sensitive radio data give an unobscured measure of this activity in distant galaxies. That supports studies of galaxy evolution from early epochs to the present.

Open data and the road to LOFAR2.0

The data set has been made publicly available. Much of its value is expected to come from combining it with observations of the same field at optical, infrared and X-ray wavelengths, which allow properties such as the distance and mass of each radio source to be estimated.

The team also regards the result as a demonstration for LOFAR2.0, the upgrade that ASTRON is carrying out with European partners. The upgrade should allow more sensitive and wider high-resolution images. De Jong argues that it will keep LOFAR competitive when the Square Kilometre Array, now under construction in South Africa and Australia, comes into operation.

As the paper is currently a preprint accepted for publication, final details may change after the publication process. The practical next steps are cross-matching studies with multiwavelength catalogues and extending the approach to wider areas once the upgraded telescope is available.

Source: Astronomers deliver the sharpest and deepest view yet of the low-frequency radio sky (Phys.org, 6 November 2026).

Image: AI-generated illustration.