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New Map of the Sky Published

Hundreds of thousands of galaxies discovered

Jülich/Dwingeloo, – 19 February 2019 – An international team of more than 200 astronomers from 18 countries has published the first maps produced by a radio sky survey with previously unprecedented sensitivity using the “Low Frequency Array” radio telescope (LOFAR). The map reveals hundreds of thousands of unknown galaxies and sheds new light on research fields such as black holes, interstellar magnetic fields, and galaxy clusters. A special issue of the scientific journal Astronomy & Astrophysics is dedicated to the first 26 articles describing the results.

Die Radiogalaxie 3C31, die von Heesen et al (2018) mit LOFAR beobachtet wurde, ist rot über einem optischen Bild dargestellt. LOFAR konnte zeigen, dass die Radiogalaxie mehr als 3 Millionen Lichtjahre groß ist. Radio galaxy 3C31, observed by Heesen et al (2018) using LOFAR, is shown in red, overlaying an optical image. LOFAR revealed that this radio galaxy is more than 3 million light years in size.
Copyright: Volker Heesen/LOFAR-Surveys-Team

LOFAR is an enormous European network of radio telescopes, which are connected to each other via a high-speed fibre-optic network and whose measuring signals are combined into a single signal. High-performance supercomputers convert 100,000 individual antennae into a virtual antenna dish with a diameter of 1,900 km. LOFAR operates in previously largely unexplored frequency ranges of approximately 10–80 MHz and 110–240 MHz. It is headed by the ASTRON research institution in the Netherlands and is considered to be the world’s leading telescope of its kind. “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,” says Dr. Carole Jackson, Director General of ASTRON. There are six measurement stations in Germany, which are operated by different scientific institutions. One of these is located to the south-east of Forschungszentrum Jülich and is run by Jülich together with the University of Bochum.

The most important results are listed here in the form of six key points::

The new sky map

Using LOFAR, the scientists have now created a new map of the sky. Many of the galaxies included in it were previously undetected because they are extremely far away and their radio signals have to travel billions of light years to reach Earth. In addition, radio waves permit the investigation of cosmic phenomena that cannot be observed in the wavelength range visible to the human eye.

LOFAR: Galaxiencluster Abell1314A new view of the universe: the image shows galaxy cluster Abell 1314. The grey colours show those parts of the sky that are visible to the human eye while the orange colours reveal the radio radiation emitted in the same part of the sky. The radio image looks completely different and changes our assumptions of how galaxies are born and develop. These objects are located approximately 460 million light years away from Earth. At the centre of every galaxy is a black hole. When matter falls into these black holes, a gigantic amount of energy is released and electrons are emitted like a jet of water. These accelerated electrons produce radio emission that can span enormous distances but is invisible at optical wavelengths.
Copyright: Rafaël Mostert/LOFAR Surveys Team/Sloan Digital Sky Survey DR13

Black holes

When scientists observe the sky with a radio telescope, they see mainly radiation from the immediate environment of black holes millions of times more massive than our sun. “We want to use LOFAR to find out what influence the black holes have on the galaxies they are located in,” says Prof. Dr. Marcus Brüggen, astrophysicist from the University of Hamburg. Prof. Dr. Huub Röttgering from Leiden University and scientific head of the sky survey adds: “And we want to find out where these black holes come from.”

When gas falls onto black holes, they emit jets of material that are visible at radio wavelengths. Thanks to the remarkable sensitivity of LOFAR, the scientific teams were able to show that these jets are present in all giant galaxies and that black holes grow constantly.

Magnetic fields

The radio radiation received by LOFAR can also be used to measure cosmic magnetic fields. Researchers from Germany were thus able to measure magnetic fields inside galaxies as well as verifying their existence between galaxies. In doing so, they also showed that enormous magnetic structures exist between galaxies. This confirms theoretical assumptions but was not previously demonstrated.

Galaxy clusters

The merging of two galaxy clusters produces radio emission known as radio halos spanning millions of light years, as Dr. Amanda Wilber from Hamburg Observatory explains: “Radio halos are produced by extremely fast elementary particles. Using LOFAR, we can investigate what cosmic accelerators produce these particles and what is powering them.”

Dr. Matthias Hoeft from the Thuringian State Observatory Tautenburg adds: “Merging galaxy clusters generate huge shock waves. With the aid of LOFAR, we can identify their radio emission and learn a lot about the gas at the edge of these gigantic galaxy clusters.”

High-quality images

JSC Distributed Storage SystemForschungszentrum Jülich is home to 15 petabyte of LOFAR data. They are stored in a distributed storage system.
Copyright: Forschungszentrum Jülich / Ralf-Uwe Limbach

The creation of radio sky maps at low frequencies demands both considerable telescope and computation time as well as large teams to analyse the data. “LOFAR produces enormous amounts of data – we have to process the equivalent of ten million DVDs of data. This places high demands on hardware and software and can only be managed by an international and interdisciplinary team,” says Prof. Dr. Dominik Schwarz from the University of Bielefeld, who is Germany’s representative on LOFAR’s steering committee.

“We worked together with Forschungszentrum Jülich in Germany in order to efficiently transform the huge amounts of data into high-quality images. These images are now public and will allow astronomers to study the evolution of galaxies in unprecedented detail,” adds Prof. Dr. Ralf-Jürgen Dettmar from the University of Bochum.

Forschungszentrum Jülich is home to almost 15 petabytes of LOFAR data. “That’s almost half of all LOFAR data, one of the largest astronomical data collections in the world. Processing these gigantic data sets poses a great challenge. What would have taken centuries on conventional computers was achieved within one year thanks to the use of innovative algorithms and extremely powerful computers,” explains Prof. Dr. Dr. Thomas Lippert, institute head of the Jülich Supercomputing Centre. Jülich is one of three data centres of the LOFAR project. In addition, the Jülich Supercomputing Centre also manages the data network traffic between the German LOFAR stations as well as with the central LOFAR computer in Groningen.


The 26 articles that have been published in a special issue of Astronomy & Astrophysics are based on only two percent of the observations planned with LOFAR. The scientists want to map the entire northern sky. They expect to find a total of approximately 15 million radio sources.

Die nahegelegene Spiralgalaxie M106 in einem optischen Bild, mit LOFAR-Radioemission überlagert.Nearby spiral galaxy M106 imaged optically overlaid with a LOFAR radio emission image. The bright emission structures at the centre of the galaxy are not real spiral arms: they are presumably due to the activity of the supermassive black hole at the centre of the galaxy.
Copyright: Cyril Tasse/LOFAR Surveys Team

LOFAR in Deutschland

Alongside the Netherlands, Germany with its six LOFAR stations is the largest international LOFAR partner. The radio telescope stations are operated by the universities of Bochum, Hamburg, and Bielefeld, as well as the Max Planck Institute for Radio Astronomy in Bonn, the Max Planck Institute for Astrophysics in Garching, the Thuringian State Observatory Tautenburg, the Leibniz Institute for Astrophysics Potsdam (AIP), and Forschungszentrum Jülich. These institutions form the German Long Wavelength (GLOW) consortium. LOFAR in Germany is funded by the Max Planck Society, the Federal Ministry of Education and Research, the respective federal states, and the European Union.

Die Jülicher LOFAR-Station DE605 besteht aus zwei Antennenfeldern zur Messung hoher und niedriger Frequenzen. Der Container in der Mitte enthält Elektronik zur Verarbeitung der Signale der einzelnen Antennen.Jülich’s LOFAR station DE605 consists of two antenna fields for measuring high and low frequencies. The container between them houses the electronics for processing the signals from the individual antennae.
Copyright: Forschungszentrum Jülich / Ralf-Uwe Limbach

Original publications:

“LOFAR Surveys”, 26 scientific articles in a 2019 special issue of the journal Astronomy and Astrophysics

Further information:

LOFAR project website

LOFAR: most common and most unique shapes of radio sources found in the LOFAR survey

Flying through the radio Universe with LOFAR (Video by Astron)

LOFAR Surveys short (Video by Astron)

Images from the LOFAR survey

Jülich Supercomputing Centre (JSC) website

Press release on the launch of Jülich’s LOFAR station, October 2011:
Rediscovering the Heavens (in German)


Dr. Thomas Fieseler,
Jülich Supercomputing Centre (JSC)
Tel.: +49 2461 61-1602

Press contact:

Dr. Regine Panknin
Forschungszentrum Jülich, Corporate communications
Tel. +49 2461 61-9054