GLOW News Blog

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

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

ArXiv: https://arxiv.org/abs/1909.12355

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

https://www.astron.nl/news-and-events

https://www.mpa-garching.mpg.de/841010/hl202007

 

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)

 

 

Together with scientists of international partner institutes, Universität Bielefeld, Hamburger Sternwarte, Landessternwarte Tautenburg are asking for the public’s help to find the origin of hundreds of thousands of galaxies that have been discovered by the largest radio telescope ever built: LOFAR. Where do these mysterious objects that extend for thousands of light-years come from? A new citizen science project, LOFAR Radio Galaxy Zoo, gives anyone with a computer the exciting possibility to join the quest to find out where the black holes at the centre of these galaxies are located.

Press releases (in German):

 

An international group of scientists led by Alexander Kappes (Institut für Theoretische Physik und Astrophysik, Universität Würzburg) succeded to measure the "hot spot advance speed" in the jet of a blazar in the early universe. Understanding the young universe is a problem with a wide field of questions and difficulties. High resolution observations in the long wavelength radio regime at unprecedented quality can be done using the LOw Frequency ARray (LOFAR) telescope to tackle these questions.

They have used LOFAR to study the distant high-redshift blazar S5 0836+710 at an angular resolution of 1 second of arc using the longest  baselines available in the international LOFAR array. LOFAR enabled them to reveal the hidden termination region of the counter-jet, which is not seen with other techniques, allowing them to probe the surrounding intergalactic medium but also the properties of the object itself, one of the most powerful active galaxies in the young universe.

hotspot

Kappes et al. (2019), Astronomy and Astrophysics, (in press)

University researchers publish study on new telescope

The Square Kilometre Array (SKA) is set to become the largest radio telescope on Earth. Bielefeld University researchers together with the Max Planck Institute for Radio Astronomy (MPIfR) and international partners have now examined the SKA-MPG telescope—a prototype for the part of the SKA that receives signals in the mid-frequency range. The study, published today (24 July) in the journal ‘Monthly Notices of the Royal Astronomical Society’, shows that the telescope is not only a prototype to test the SKA design, but can also be used on its own to provide insights into the origin of the Universe. The German Federal Ministry of Education and Research (BMBF) is funding the work on the SKA-MPG through a joint research project coordinated by Bielefeld University.

 

Read the full text with further information under the following links:

Press release of Bielefeld University (in English)

Pressemitteilung der Universität Bielefeld (auf Deutsch)

Publication in Monthly Notices of the Royal Astronomical Society (in English) 

Ein internationales Astronomieteam hat in einer unserer Nachbargalaxien verschwunden geglaubten Wasserstoff wiedergefunden.

 

Die Galaxie NGC 1316 ist in der Astronomie sehr bekannt. Trotzdem gibt sie der Forschung seit 20 Jahren Rätsel auf: Theoretische Berechnungen besagen, dass sie viel Wasserstoff enthalten müsste, der bisher aber nicht nachgewiesen werden konnte. In einer aktuellen Untersuchung unter der Federführung von Prof. Dr. Paolo Serra vom italienischen Istituto Nazionale di Astrofisica, an der ein Team der Ruhr-Universität Bochum (RUB) um Dr. Peter Kamphuis beteiligt war, haben Astronomen den Wasserstoff jetzt gefunden. Aus den Ergebnissen können sie eine genauere Theorie zur Bildung von Galaxien ableiten. Sie berichten in der Zeitschrift Astronomy and Astrophysics vom 22. Juli 2019.

Weitere Informationen:

Vollständige Pressemitteilung der Ruhr-Universität Bochum

Veröffentlichung in Astronomy and Astrophysics (auf Englisch)

Radioteleskop entdeckt „Nadeln“ in Gewitterblitzen

Mit dem Radioteleskop LOFAR hat ein internationales Forscherteam überraschende Strukturen von Gewitterblitzen in der Erdatmosphäre entdeckt. Diese „Nadeln“ können Gewitterwolken wieder aufladen, so dass sie sich nach kurzer Zeit an derselben Stelle ein zweites Mal entladen. Das Team unter Leitung von Brian Hare und Olaf Scholten von der Universität Groningen in den Niederlanden stellt das bisher unbekannte Phänomen im Fachblatt „Nature“ vor. An der Arbeit sind auch deutsche Forscherinnen und Forscher aus dem German Long Wavelength Konsortium und von DESY Zeuthen beteiligt.

Das Low Frequency Array LOFAR ist ein dezentrales Radioteleskop, das aus tausenden einfachen Antennen besteht. Zugehörige Antennenfelder befinden sich in vielen europäischen Ländern, in Deutschland etwa am Forschungszentrum Jülich und in Norderstedt bei Hamburg. Diese Antennen sind über Glasfasernetze miteinander verbunden und an Hochleistungsrechner angeschlossen. Diese Verbindung erlaubt es, die Antennen zusammenzuschalten und als ein riesiges, virtuelles Teleskop zu nutzen.

LOFAR dient in erster Linie zu astronomischen Beobachtungen. Allerdings ist die Anlage sehr flexibel, so dass sie sich auch zur Messung von Blitzen eignet. „Wir messen Frequenzen von 30 bis 80 Megahertz, liegen also genau zwischen dem Kurzwellen- und dem Ultrakurzwellenbereich“, berichtet Hare. „Mit diesen weltweit einzigartigen Daten konnten wir zum ersten Mal Blitze so genau auflösen, dass einzelne physikalische Prozesse sichtbar wurden. Durch die Benutzung von Radiowellen konnten wir auch ins Innere der Gewitterwolken schauen, wo sich die spannenden Prozesse abspielen.“

Blitze entstehen, wenn innere Turbulenzen verschiedene Teile großer Cumulonimbus-Wolken gegeneinander elektrisch aufladen. Der Effekt ist vergleichbar mit der aus dem Alltag bekannten statischen Aufladung. Wird der Spannungsunterschied zwischen positiven und negativen Wolkenteilen zu groß, kommt es zu einer plötzlichen Entladung, die wir als Blitz sehen können. Dabei entsteht zunächst in einem kleinen, punktförmigen Bereich ein Plasma, also ein elektrisch leitfähiges Gas, das sich dann zu Kanälen ausbreiten kann. Die Spitze eines solchen Plasmakanals kann positiv oder negativ geladen sein. Es war bekannt, dass negative Kanäle besonders viele Radiowellen an der Spitze aussenden, wohingegen positive Kanäle dies an der Spitze kaum tun.

LOFAR erlaubt es, die Radiowellen, die ein Blitz aussendet, in ihrer ursprünglichen Form unverarbeitet zu speichern. Dies wiederum ermöglicht es, neue bildgebende Verfahren zu entwickeln, die aus den Rohdaten ein dreidimensionales Bild eines Blitzes zeichnen können – zehnmal besser als bisherige Messungen, bis zu einem Meter genau und dank Radiowellen innerhalb einer Wolke, die vom Teleskop bis zu 20 Kilometer entfernt sein kann.

Die Messungen stammen ursprünglich aus unserer Forschungsgruppe, die sich mit kosmischer Strahlung beschäftigt“, berichtet Ko-Autorin Anna Nelles von DESY. „An der Schnittstelle zwischen Teilchenphysik und Astronomie war dieses Gebiets bereits recht exotisch für ein Radioteleskop. LOFAR wurde ja vor allem für die Astronomie gebaut. Dass wir nun das beste Blitz-Interferometer der Welt sind, kam für alle überraschend und zeigt, welche spannenden Möglichkeiten sich durch Grundlagenforschung mit herausragender Infrastruktur ergeben können.“

Die Beobachtungen enthüllen bisher unbekannte, nadelförmige Strukturen. Wenn Blitze sich ausbreiten, entladen sie die Gewitterwolken nur an einigen Stellen. Die nun entdeckten Nadeln erlauben, dass elektrische Ladungen gespeichert werden, und ermöglichen damit, dass eine Gewitterwolke an der gleichen Stelle mehrfach entladen werden kann. „Unsere Erkenntnisse stehen im Widerspruch zum bisherigen Verständnis von Blitzen, in dem Ladung entlang von Plasmakanälen von einer Wolke zur anderen fließt“, berichtet Scholten. „Nur durch die unübertroffen genauen Messungen mit LOFAR konnten wir zeigen, dass sich entlang der positiven Kanäle kleine Seitenkanäle bilden, die besonders helle Radiowellen aussenden, was bedeutet, dass dort Ladung fließt.“

In diesen Nadeln sammelt sich Ladung, die dann anschließend nicht wie erwartet in die negativen Kanäle fließt, sondern über die Nadeln in die Wolke zurückgepumpt wird. Dadurch lädt sich die Wolke erneut auf,“ ergänzt Hare. „Wir sehen eine immense Anzahl an Nadeln in unseren Beobachtungen. Dies wiederum zeigt uns, wie sich Wolken nach einer Blitzentladung so schnell wieder aufladen können. Daher kommt es aus einer Wolke zu wiederholten Blitzeinschlägen auf dem Boden, und Gewitter liefern nicht nur einen Blitz, sondern viele spektakuläre, aber auch gefährliche Entladungen.“

Hintergrund:
Deutschland ist neben den Niederlanden mit sechs Stationen der größte internationale Partner bei LOFAR. Die Radio-Teleskop-Stationen werden betrieben von: der Universität Bielefeld, der Ruhr-Universität Bochum, der Universität Hamburg, dem Max-Planck Institut für Radioastronomie in Bonn, dem Max-Planck Institut für Astrophysik in Garching, der Thüringer Landessternwarte, dem Astrophysikalischen Institut Potsdam und dem Forschungszentrum Jülich. Gefördert wird LOFAR in Deutschland von der Max-Planck-Gesellschaft, dem Bundesministerium für Bildung und Forschung, den zuständigen Ministerien der beteiligten Bundesländer, darunter das Ministerium für Kultur und Wissenschaft des Landes Nordrhein-Westfalen, und von der Europäischen Union.

Pressemitteilung des DESY (mit Videos): http://www.desy.de/aktuelles/news_suche/index_ger.html?openDirectAnchor=1619&two_columns=0

Originalveröffentlichung: Needle-like structures discovered on positively charged lightning branches; Brian Hare, Olaf Scholten et al.; „Nature“, 2019; DOI: 10.1038/s41586-019-1086-6

 

 

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