LOFAR sky map reveals a flurry of new discoveries
Jülich, 25 February 2022 - For seven years, an international research team has collected radio signals from space. The data have now been published as a new sky map, which provides a unique picture of the wonders of our universe. For the first time, 4.4 million galaxies were made visible in the radio wave range. One million of these galaxies were previously completely unknown. The discoveries were made using the European LOFAR telescope, the largest radio telescope ever built. The Jülich supercomputer JUWELS, currently the fastest supercomputer in Europe, helped to process the gigantic data sets with its enormous computing power.
Intergalactic particles
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By using the European radio telescope LOFAR, the researchers have mapped around a quarter of the northern sky in unprecedented resolution and made it accessible to the public online https://lofar-surveys.org/. The vast majority of these objects are billions of light years away and are either galaxies that harbour massive black holes or are rapidly growing new stars. Rarer objects that have been discovered include colliding groups of distant galaxies and flare stars within the Milky Way.
Remains of a supernova
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"This project is so exciting to work on. Each time we create a map, our screens are filled with new discoveries and objects that have never before been seen by human eyes," says Timothy Shimwell from the Netherlands Institute for Radio Astronomy (ASTRON) and Leiden University.
New members in the galaxy zoo
The wealth of new information contained in the maps is evident from a host of recent scientific publications that make use of the radio images. For example, the team today published the largest ever studies of colliding galaxy clusters comprising between hundreds and thousands of galaxies - the universe's largest structures.
Crash of the galaxies
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Previous results include: finding curious signals from nearby stars that may be induced by orbiting exoplanets; pinpointing the slowest spinning pulsar that challenges current theories describing such objects; observing so called "jellyfish galaxies" shedding material as they travel through the surrounding medium; and discovering so many radio galaxies of all shapes, sizes, and ages that a citizen science project has been set up to help find new black holes in this zoo of objects.
Jellyfish galaxy
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Data to fill 20,000 laptop hard drives
Whilst these discoveries are already refining our understanding of the universe, it is also clear that the research conducted to date merely scratches the surface of what is yet to come. The data that have been released only represent 27 percent of the entire survey. Nevertheless, they are based on really large data sets. To produce the map, researchers processed 3,500 hours of observations that occupy 8 petabytes of disk space - the equivalent to roughly 20,000 laptops. A large part of this, over 60 percent, comes from the LOFAR long-term archive at the Jülich Supercomputing Centre (JSC). The JSC at Forschungszentrum Jülich is one of three data centres participating in the project. It hosts about onef third of the LOFAR data archive, which totals around 55 petabytes.
JUWELS supercomputer at the Jülich Supercomputing Centre
Copyright: Forschungszentrum Jülich / Wilhelm-Peter Schneider
"In order to make sense of this enormous amount of data generated by the LOFAR telescope, high-performance computers stationed throughout Europe are used. A major challenge is the calibration of the measured signals, for which we were able to access the Jülich supercomputer JUWELS, which has a computing capacity equivalent to 300,000 modern PCs," says Matthias Hoeft of the Thuringian State Observatory in Tautenburg. "This is an important task. In a first step, interfering influences on the signals are determined from the measurement data using cutting-edge algorithms. These disturbances are filtered out if necessary, so that the actual brightness distribution of the sky can be reconstructed for scientific evaluations."
Prospect of further findings
The LOFAR data are available to researchers worldwide. Many more scientific breakthroughs are expected in the future. "The link with observations from other frequency ranges can, for example, provide new insights into the properties of dark energy, which are still poorly understood. They also enable new insights into the formation of galaxies and even larger structures in the universe," says cosmologist Dominik Schwarz from Bielefeld University, who is coordinating Germany's contribution to LOFAR.
Highly energetic universe
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Scientists from the Ruhr University Bochum (RUB) also use the LOFAR data to study the evolution of galaxies and dwarf galaxies with extremely high star formation rates. "The completely new technology of the LOFAR radio telescope opens up many new possibilities for us to study high-energy physical processes in the world of galaxies," says RUB researcher Ralf-Jürgen Dettmar.
Whale galaxy
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Research teams at the universities in Hamburg and Bielefeld and the Observatory in Tautenburg, meanwhile, are studying gigantic radio sources to investigate the origin of magnetic fields in the cosmos. "One result that has already been obtained by using the data is that the magnetic fields in the universe must have grown to their current strength at quite an early stage. The reason for this is that chaotic gas movements rapidly strengthen the magnetic fields in a process known as dynamo amplification," says Marcus Brüggen from the Hamburg Observatory.
Early quasar
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Virtual telescope LOFAR
LOFAR, the Low Frequency Array, is controlled by the ASTRON institute in the Netherlands and is the forerunner of a new type of radio telescope. It consists of more than 50 stations across seven European countries that are connected to powerful supercomputers via fast fibre optic connections. The enormous computing power is needed to combine the signals from the many thousands of individual antennas. This results in a virtual antenna dish with a diameter of 1,900 kilometres, which is able to distinguish between very weak signals and signals that are very close to each other.
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: Ralf-Uwe Limbach
In Germany, six stations are operated by different scientific institutions. One of them is located southeast of the Forschungszentrum Jülich campus and is operated by the JSC together with Ruhr University Bochum. In addition, the JSC manages the data network traffic between the German LOFAR stations and the central LOFAR computer in Groningen via modern fibre-optic multiplexing connections.
View into the tape archive: Forschungszentrum Jülich holds around 17 petabytes of the LOFAR data archive, which totals around 55 petabytes.
Copyright: Ralf-Uwe Limbach
Original publication:
T. W. Shimwell, M. J. Hardcastle, C. Tasse, P. N. Best, H. J. A. Röttgering, W. L. Williams, A. Botteon, A. Drabent, A. Mechev, A. Shulevski, R. J. van Weeren et al.
The LOFAR Two-metre Sky Survey (LoTSS). V. Second data release
Astronomy & Astrophysics (published online 25 February 2022), DOI: 10.1051/0004-6361/202142484
