GLOW News Blog

News about the German Long Wavelength Consortium and radio astronomy in Germany


Galaxy Cluster Abell 194. The MeerKAT radio image taken at wavelenghts 18-33 cm is shown in orange, with an optical image dominated by normal galaxies shown in white.      Image credit: SARAO, SDSS.

The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) has released a first comprehensive paper (Knowles et al. 2021), publishing more than 50 newly discovered, astonishing patches of radio emission in galaxy clusters. One of the released images shows two giant radio galaxies (more than one million light-years from end to end) at the center of a large group of galaxies in the cluster Abell 194, revealing the presence of relatively narrow magnetic filaments in the region, as well as complex interactions between the radio emission from the two galaxies. “The quality of the radio images from MeerKAT located in the South African Karoo desert is breathtaking. The level of detail that can now be seen is really transformative for our understanding of cosmic plasmas" says Prof. Marcus Brüggen of Hamburger Sternwarte, who is one of the 40 scientists participating in this Survey.  This 'astronomical bonanza' contains also many emission regions, which are yet not well understood. Some are  isolated features, illuminating winds and intergalactic shock waves in the surrounding plasma. The MGCLS will contribute to research areas as the regulation of star formation in galaxies, the physical processes of jet interactions, and the study of faint cooler hydrogen gas – the fuel of stars – in a variety of environments.


More information:

On October 15th 2021, the PUNCH4NFDI consortium held a workshop to formally kick-off its initial 5-year work programme. PUNCH4NFDI (Particles, Universe, NuClei, and Hadrons for the Nationale ForschungsDaten-Infrastruktur) is one of several consortia within the German National Research Data Infrastructure, which had its inception just a year earlier. Over the coming years, PUNCH4NFDI will set up a federated storage and computing infrastructure, as well as a variety of associated services, to be used by researchers of several fields in physics that face similar data challenges. Astronomy and astroparticle physics are just two of those fields, and several GLOW members are among the diverse group of universities and research institutes that constitute this consortium. We look forward to a fruitful collaboration and welcome the great synergetic potential that this exciting initiative offers to our research community.

A Large Programme Portfolio will be composed in order to prepare for the significant LOFAR2.0 upgrade of the International LOFAR Telescope (ILT). There will be online information sessions on


The full science community is invited to attend.

The status of the LOFAR2.0 development programme and the process of defining LOFAR2.0 Large Programmes will be presented in these information sessions. Note that the info session programme is identical on both days and is repeated in order to facilitate live participation. Substantial time has been planned for questions and discussion. The sessions will also be recorded.

Large LOFAR2.0 observing programmes are expected to be coordinated by expert LOFAR users in partner countries, but must benefit the broad community and satisfy various criteria to facilitate maximal science return.  An open call will be issued for brief Expressions of Interest, due towards the end of 2021, with a further programme definition and selection process in 2022, involving independent peer review.

Further info:
Please e-mail This email address is being protected from spambots. You need JavaScript enabled to view it. or This email address is being protected from spambots. You need JavaScript enabled to view it. with LOFAR2.0 Info Session as a Subject to receive the Zoom link.

After almost a decade of work, an international team of astronomers has published the most detailed images yet seen of galaxies beyond our own, revealing their inner workings in unprecedented detail. The images were created from data collected by the Low Frequency Array (LOFAR), a network of more than 70,000 small antennae spread across nine European counties, with its core in Exloo, the Netherlands. The results come from the team’s years of work, led by Dr Leah Morabito at Durham University.

The 70,000+ LOFAR antennae spread across Europe are combined to create a ‘virtual’ telescope with a collecting ‘lens' with a diameter of almost 2000 km, which provides a twenty-fold increase in resolution in comparison with observing with Dutch stations only. The six LOFAR stations run by GLOW (Jülich, Effelsberg, Tautenburg, Unterweilenbach, Potsdam, and Norderstedt) provided essential observational coverage because of their geographical location within the International LOFAR telescope, which is indispensable to make images at such a high resolution.

The team’s work forms the basis of nine scientific studies that reveal new information on the inner structure of radio jets in a variety of different galaxies as well as a publication describing the publicly-available data-processing pipeline, developed with assistance from GLOW members, in detail. This will allow astronomers from around the world to use LOFAR to make high-resolution images with relative ease.

Since LOFAR must stitch together the data gathered by more than 70,000 antennae, processing is a huge computational task. To produce a single image, more than 13 terabits of raw data per second – the equivalent of more than a three hundred DVDs – must be digitised, transported to a central processor and then combined. This is a challenge that can only be mastered with supercomputers. The Forschungszentrum Jülich hosts one of the LOFAR Long-Term Archives that stores about half of all observations conducted with the LOFAR telescope.


Figure: Illustration of the gain in resolving power if using the full LOFAR-VLBI network including all European stations. The inner structure of the radio galaxy is not visible in the upper central image at 6‘‘ resolution (using the Dutch stations only). With the full LOFAR-VLBI array it is possible to achieve a resolution of about 0.3‘‘ allowing the observer to reconstruct unprecedented details of the inner structure of radio galaxies.

Revealing a hidden universe of light in HD

The new images, made possible because of the international nature of the collaboration, pushing the boundaries of what we know about galaxies and super-massive black holes. Super-massive black holes can be found lurking at the heart of many galaxies and many of these are ‘active’ black holes that devour in-falling matter and belch it back out into the cosmos as powerful jets and outflows of radiation. These jets are invisible to the naked eye, but they burn bright in radio waves and it is these that the new high-resolution images have focused upon. Dr Neal Jackson of The University of Manchester, said: “These high resolution images allow us to zoom in to see what’s really going on when super-massive black holes launch radio jets, which wasn’t possible before at frequencies near the FM radio band”.

"We are very happy that many years of hard work enable us now to efficiently process all European LOFAR stations in a way to make use of the highest possible resolution the LOFAR telescope is able to provide. This allows us to gain breathtaking images from the inner-most regions of radio galaxies", said Dr Alexander Drabent from the Thüringer Landessternwarte in Tautenburg, "With this step, LOFAR enters still unknown territory at such low frequencies".


Links: Press Release (ASTRON)

The extremely heavy rain in the Eifel region on July 14 and 15, 2021, also hit the Effelsberg radio observatory. The "low-band" part of the Effelsberg station of the European LOFAR telescope network was completely flooded by two usually tiny creeks. More details


Recently, the Low-Frequency ARray (LOFAR) has been used to search for the elusive dark matter in dwarf spheroidal galaxies using radio continuum observations. One of the leading dark matter candidates are the weakly interacting massive particles (WIMPs), which can produce via several annihilation channels cosmic-ray electrons. With the micro-Gauss magnetic field strengths we expect in galaxies, these electrons generate non-thermal synchrotron emission that peaks in the range of hundreds of MHz. With a new 8-hour observation at 150 MHz as part of the LOFAR Two-metre Sky Survey (LoTSS), upper limits for the radio continuum emission in the dwarf spheroidal galaxy Canes Venatici I (CVnI) were obtained. These can be converted into new upper limits for the cross-section of WIMPs. LOFAR has quite good sensitivity, so that for a reasonable choice of model parameters such as magnetic field strength and comic-ray diffusion coefficient, the limits are comparable with those set by the Fermi Large Area Telescope using gamma-ray observations of this particular galaxy. The benchmark limits of this new work exclude already several thermal WIMP realizations in the [2, 20]-GeV mass range.

Figure. (a) 150-MHz map of Canes Venatici I observed with LOFAR, where the large circle shows the extent of the stellar disc and the small circles show the position of background sources; these were subtracted from the map to search for the diffuse emission from annihilating WIMPs. (b) new resulting cross-section of WIMPs annihilating into electron–positron pairs. Several models with various magnetic field strengths and diffusion coefficients are presented.

Reference: Vollmann et al. (2020), MNRAS, 496, 2663


An international team of astronomers, led by Junior Professor Francesco de Gasperin from Universität Hamburg, has produced the largest and sharpest map of the sky at ultra-low radio frequencies. The map published in the journal Astronomy & Astrophysics reveals more than 25,000 active supermassive black holes in distant galaxies.

At a first glance, the map looks like an image of a starry night sky. However, the map is based on data taken by the radio telescope LOFAR and shows the sky in the radio band. Stars are almost invisible in the radio band, but instead black holes dominate the picture. With this map, astronomers seek to discover celestial objects that only emit waves at ultra-low radio frequencies. Such objects include diffuse matter in the large scale structure of the Universe, fading jets of plasma ejected by supermassive black holes, and exoplanets whose magnetic fields are interacting with their host stars. Albeit among the largest of its kind, the published map only shows two percent of the sky. The search for these exotic phenomena will continue for several years until a map of the entire northern sky will be completed. 

The radio waves received by LOFAR and used for this work are up to six meters long which corresponds to a frequency of around 50 MHz. They are the longest radio waves ever used to observe such a wide area of the sky at this depth. “The map is the result of many years of work on incredibly difficult data. We had to invent new strategies to convert the radio signals into images of the sky, but we are proud to have opened this new window on our Universe.”, says Francesco de Gasperin, scientist at the Hamburg Observatory and leading author of the publication.

There is a reason why the Universe at these long radio wavelengths is almost uncharted: such observations are very challenging. The ionosphere, a layer of free electrons that surrounds the Earth, acts as a lens continuously moving over the radio telescope. The effect of the ionosphere can be compared to trying to see the world while being submerged in a swimming pool. Looking upwards, the waves on the water bend the light rays and distort the view. To account for ionospheric disturbances, the scientists used supercomputers and new algorithms to reconstruct its effect every four seconds over the course of 256 hours of observation.

LOFAR is currently the largest radio telescope operating at lowest frequencies that can be observed from Earth. It consists of 52 stations spread across nine different countries: The Netherlands, Germany, Poland, France, United Kingdom, Sweden, Ireland, Latvia, and Italy. LOFAR is a joint project of ASTRON, the Netherlands Institute of Radio Astronomy, and the universities of Amsterdam, Groningen, Leiden, Nimwegen as well as the German Long Wavelength Consortium (GLOW) to which Universität Hamburg belongs.

Fig. : LOFAR image of the cluster PSZ2G091.83+26.11 at a redshift of z=0.822. The brightness of the emission is outlined by the contour lines overlayed.

From a study of nine ancient galaxy clusters with the radio telescope LOFAR, a group of European radio astronomers concluded that the built-up of magnetic fields must have been fast during the formation of the clusters. The observations were taken from the ongoing LOFAR Two-metre Sky Survey (LoTSS), which has surveyed currently about 40% of the Northern Sky. The group, led by Gabriella Di Gennaro from Leiden Observatory (Netherlands), included several members from GLOW institutes. They selected distant clusters, which emitted their radio light when the Universe was only half of its present age, and compared them with local galaxy clusters. They then found that the luminosities of the diffuse radio emission associated with the ancient clusters are similar to those of the local ones. As the magnetic field strength in the diffuse regions is correlated with the luminosities, the observations infer that the magnetic field strengths (which are of the order of a few microgauss) must have been created rapidly in the young universe and did not evolve further until today. These findings were recently published in Nature Astronomy.  "The study shows the potential of LOFAR's sensitive low-frequency observations to uncover the role of magnetic fields in the formation of the largest structures in the Universe", comments co-author and GLOW chair Matthias Hoeft (Thüringer Landessternwarte, Germany).

Find more information at Leiden University: Astronomers see gigantic collisions of galaxy clusters in young universe

On 12 June 2020, LOFAR celebrates its 10th anniversary. Ten years to the day ago, Queen Beatrix of the Netherlands inaugurated the telescope and witnessed the signing of the Memorandum of Understanding with the international partners. The LOFAR telescope is the world’s largest low-frequency instrument and is one of the pathfinders of the Square Kilometre Array (SKA), which is currently being developed. Throughout its ten years of operation, LOFAR has made some amazing discoveries. It has been a key part of groundbreaking research and development, both in astronomy and engineering. 

Operating six international LOFAR stations, hosting a large part of the instrument’s long-term archive and providing computing resources on the JUWELS supercomputer at the FZ Jülich, GLOW member institutes have since the beginning been a key partner in developing the array and participated in many of the pioneering research projects. You can find some of the recent achievements on our Science Highlights page

Crucial for the German participation was BMBF funding via the “Verbundforschung für erdgebundene Astrophysik’’ as well as substantial contribution by the Max-Planck society, the Thuringian state observatory and a number of universities.

LOFAR is not getting old, its next level is currently under development. Framed as LOFAR 2.0, the telescope is going to increase its efficiency and sensitivity to remain the leading low-frequency telescope with unmatched angular resolution for the next decade.

See more information on


Pareidolia is a tendency that pushes humans to see shapes in clouds or faces in inanimate objects. The picture shown here is a composition of four cosmic radio sources that can in fact look like a scary monster. To obtain this effect, the sources have been rearranged compared to their original position in the sky but their apparent sizes were preserved. However, in some sense, these sources are real monsters. Their names are: Cassiopeia A (top left), Taurus A (top right), Cygnus A (center), and Virgo A (bottom). These are the four most powerful radio sources in the northern hemisphere. Historically, the brightest radio sources in the sky were named after the constellation in which they were found followed by a letter starting with an "A". They were then grouped in the so-called A-team, like the famous TV series from the 80s.

The nature of these four sources is very diverse. The eyes of the monster (Cassiopeia A and Taurus A) are two supernova remnants: the leftovers of the explosions of two stars in our own Galaxy. The evil pupil that stares at you in Taurus A is the Crab pulsar. The nose of the monster, Cygnus A, is an extremely powerful radio galaxy 600 million light years away, whose two lobes are powered by jets of energetic particles formed near a supermassive black hole. The mouth of the monster (Virgo A) is the extended structure (larger than an entire galaxy) that surrounds the famous supermassive black hole at the centre of the galaxy M87, the same black hole recently imaged by the Event Horizon Telescope.

These four sources are well known to radio astronomers, but this is the first time that they were able to see them in such great detail at the extremely long wavelengths of 5 meters, close to the longest wavelength we can observe with ground instruments. But what does it mean to see a source at “long wavelength”? While we can directly observe the sky with our naked eyes, capturing electromagnetic radiation at visible wavelengths, some cosmic sources emit also (or only) at very different wavelengths, all the way from radio waves to gamma-rays. To make radio images, astronomers need to use radio telescopes, instruments that are similar to optical telescopes but built to capture specifically radio waves. Using this information, astronomers can reconstruct the structure of a radio source as we would see it if we had “radio sensitive” eyes. The images used to make the radio monster were obtained with the Low Frequency Array (LOFAR), a pan-European radio telescope made by 52 stations spread across 8 different countries (The Netherlands, Germany, France, UK, Poland, Sweden, Latvia, Ireland, and soon Italy) and coordinated by a supercomputer in Groningen (NL).

Reference: de Gasperin et al. 2020 (A&A 635, A150)



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