The German Long Wavelength Consortium

A giant radio halo associated with the Perseus galaxy cluster

Galaxies can be considered as islands in space, but they are not entirely isolated. Where galaxies assemble to large associations with up to several thousand members, known as galaxy clusters, they are embedded in diffuse regions called the intracluster medium (ICM). In general this medium is of such a low density that it is rarely optically visible. On the other hand the medium is permeated by magnetic fields, which force cosmic-ray electrons which enter the cluster, to propagate on curved trajectories. This movement leads to loss of energy which is emitted in form of synchrotron radiation. This radiation is emitted at long wavelengths in the centimeter to meter range. It forms a 'radio halo' centered on the galaxy cluster and can be detected by sensitive radio telescopes on Earth.

Near-infrared image of the Perseus cluster with the 144 MHz LOFAR radio halo image is overlaid in red. The infrared image was observed by the Euclid satellite. (Source: van Weeren et al. 2024).

With LOFAR a group of radio astronomers led by Reinout van Weeren from Leiden Observatory studied a prominent example of such a 'radio halo'. It was detected towards one of the closest galaxy clusters located in the Perseus constellation (see Figure). The detailed analysis of the halo at different spatial resolutions allowed to find many details, which can be attributed to a past off-center collision with another galaxy cluster and to the movement of the galaxies within the cluster. Its giant size indicate that even in the outskirts of galaxy clusters such as in Perseus enough turbulent energy is available to re-accelerate electrons.

Reference: Van Weeren et al. 2024, Astronomy & Astrophysics 692, A12

LOFAR ERIC founded

The Low Frequency Array (LOFAR) world’s largest and most sensitive radio telescope operating at low radio frequencies. LOFAR was previously organised as a project and is now being transformed into an independent legal form: a consortium for a European research infrastructure (European Research Infrastructure Consortium, ERIC). The European Commission had decided to set up LOFAR as an ERIC due to the Europe-wide significance of the radio telescope. LOFAR ERIC was officially founded 22 January 2024.

Ten years ago, the LOFAR radio telescope went into operation. Today, It is a Europe-wide distributed research infrastructure that consists of 52 antenna stations in eight European countries. In Germany, six international LOFAR stations are operating, which consist of a low-band (10–90 MHz) and high-band (110–250 MHz) antenna array, each with a diameter of 70 metres. The joint project revolutionised low-frequency radio astronomy research and led to an avalanche of scientific publications.

Six EU countries applied to the European Commission to set up LOFAR ERIC and are therefore its founding members: Bulgaria, Germany, Ireland, Italy, the Netherlands and Poland. The new research organisation collaborates with institutes in France, Latvia, Sweden and the United Kingdom. Its statutory seat is in Dwingeloo, at the Netherlands Institute for Radio Astronomy (NWO-I/ASTRON), where the LOFAR radio telescope was originally constructed. LOFAR ERIC has been officially launched there today, when the first Council meeting of the new research organisation took place.

LOFAR ERIC will modernise the distributed infrastructure, and serve the astronomy community with a cutting-edge suite of observing and data processing capabilities, rooted in its vast field of view on sky, unprecedented sensitivity and image resolution, and novel capabilities to observe in multiple directions all at once.

"The fact that LOFAR ERIC opens the window to the stars is not only of great and excellent value for science, but also for European research policy," says Professor Dr. Dominik Schwarz from Bielefeld University. As a member of the German Long Wavelength Consortium (GLOW), he played a key role in setting up the new research institution - both as Vice-Chairman of the Board of the International LOFAR Telescope (ILT) and as a representative of German science on the LOFAR ERIC's development committee. "We have spent half a decade working towards the establishment of LOFAR. This has now been rewarded," explains Schwarz.

"The establishment of LOFAR ERIC consolidates world-leading excellence for Europe in an important research field," said Dr. René Vermeulen, founding director of LOFAR ERIC. "With its unrivalled distributed research infrastructure and its robust pan-European partnership, LOFAR ERIC enters the European Research Area as a powerhouse at the cutting edge of astronomy science and technology, with the potential to contribute to broader complex challenges."

The new LOFAR facility will empower researchers to pursue large-scale innovative projects across scientific domains. This includes research into the early phase of the universe, the formation and evolution of galaxies, the physics of pulsars and transient radio phenomena. Other research topics include the nature of ultra-high energy cosmic particles, the conditions in the interstellar medium, and the structure of cosmic magnetic fields. Furthermore, LOFAR ERIC contributes unique scientific insights into various topics with societal relevance, such as lightning, ionospheric disturbances and space weather.

As a research organisation with a long-term perspective, LOFAR ERIC provides the European and global community with reliable access to a wide range of scientific research services. LOFAR ERIC will facilitate access to its extensive science data products through its user-friendly, publicly accessible archive.

The German universities and research institutes participating in LOFAR ERIC are: the Universities of Bielefeld, Bochum, Erlangen-Nuremberg, Hamburg and Würzburg as well as the Research Center Forschungszentrum Jülich, the Leibniz Institute for Astrophysics Potsdam, the Max Planck Institute for Astrophysics in Garching, the Max Planck Institute for Radio Astronomy in Bonn and the Thüringer Landessternwarte Tautenburg.