The radio galaxy 3C31, observed with LOFAR by Heesen et al (2018), is shown in red on top of an optical image. LOFAR reveals the radio galaxy to be more than 3 million light years in size.
Credit: Volker Heesen and the LOFAR surveys team.
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Research
Eavesdropping into the skies
51 stations, scattered across Northern Europe and linked via fibre optics, form the huge virtual receiving antenna of the LOFAR radio telescope. Since 2010, astronomers have discovered hundreds of thousands of galaxies and gained countless scientific insights with it.
How LOFAR works
LOFAR, the precursor of a new type of radio telescope, uses many thousands of interconnected small antennas instead of a single large receiving dish. They are grouped into 51 so-called stations: fields with hundreds of simple antennas no more than 1.7 metres high. The stations are located in the Netherlands, in Germany, France, Sweden, Great Britain, Poland and Ireland. The DE605 station is located directly southeast of Forschungszentrum Jülich.
Fast optical fibre links transport the measurement signals of all stations to supercomputers. These sort the signals of all individual antennas and connect them to form a virtual receiving dish with a diameter of 1,900 kilometres. With it, even weak signals that hit the earth very close together can be distinguished. The measurements generate vast amounts of data. It would take conventional computers centuries to process them; thanks to supercomputers and innovative algorithms, processing takes one year.
LOFAR is coordinated by the Dutch research institute ASTRON.
Listening to the universe
In space, besides the visible light of the stars, there are also other forms of electromagnetic radiation. These include radio waves. In contrast to light, radio signals also penetrate dust and gas clouds between the stars. Radio telescopes on earth can receive these signals, which provide valuable information about invisible areas in space. The larger the collecting surface, the better the telescope can resolve the details of the signals. The radio telescope LOFAR (short for “Low Frequency Array”) measures radio waves in a wavelength range that was, in previous years, largely unexplored: from 1 to 10 metres.
1.00petabytes of LOFAR data is how much Forschungszentrum Jülich houses. This is about a third of all LOFAR data, corresponding to about 15 billion mobile phone photos.
A new sky map
An international team of scientists has converted the radio signals received by LOFAR into visible images. This cost enormous amounts of telescope and computing time. With the aid of supercomputers – including Jülich – the researchers created a new, publicly accessible sky map from these images. The map also shows many previously unknown galaxies, which are often billions of light years away. It allows astronomers to study the evolution of galaxies in unprecedented detail, and this is just the beginning: the current map covers only two per cent of the area of the sky that is to be captured with LOFAR.
Black holes
The LOFAR data show that there is a massive black hole in the centre of most galaxies. It reveals itself by so-called jets – rays of matter generated by magnetic fields encircling the black hole. “With LOFAR, we can count the number of supermassive black holes in space and follow their cosmic evolution,” explains Prof. Ralf-Jürgen Dettmar of Ruhr Universität Bochum, one of the astronomers involved. Hence, the scientists hope to be able to clarify in the future where black holes come from and what influence they have on the galaxies in which they are located. Using the LOFAR data, the researchers have already been able to show that black holes are constantly growing.
“The LOFAR data is one of the largest astronomical data collections in the world.”
Prof. Thomas Lippert, Director of the Jülich Supercomputing Centre, one of three LOFAR data centres
Cosmic magnetic fields
With the aid of LOFAR, astronomers from Germany have discovered that magnetic fields exist not only within galaxies, but also between them. Although this had previously been suspected, it had not yet been proven. LOFAR even provided evidence that the entire space between the galaxies could be magnetic.
Other phenomena
LOFAR can also be used to study pulsars, galaxy clusters and solar activity. However, the telescope also receives radio signals of earthly origin: for example, researchers used it to discover new processes in the formation of lightnings.
Texts: Frank Frick
Pictures of the universe based on the LOFAR data
The radio source B3 0157+405A as seen in the LoTSS wide-area survey. Complex structure in the radio lobes indicates the presence of large-scale turbulent structure in the magnetic fields inside them.
Credit: Maya Horton and the LOFAR surveys team.
The spiral galaxy M51 in the HETDEX region.
Credit: Tim Shimwell and the LOFAR surveys team.
This image shows how the LOFAR radio telescope opens a new view of the universe. The image shows galaxy cluster Abell 1314. In shades of grey, a piece of the sky can be seen as we know it in visible light. The orange hues show the radio emitting radiation in the same part of the sky. The radio image looks completely different and changes our assumptions about how galaxies arise and develop. These objects are located at a distance of approximately 460 million light years from earth. In the middle of every galaxy there is a black hole. When matter falls into it, an unbelievable amount of energy is released and electrons are ejected like a fountain. These accelerated electrons produce radio emission that can extend over gigantic distances and is not visible at optical wavelengths.
Credit: Rafaël Mostert/LOFAR Surveys Team/Sloan Digital Sky Survey DR13
The galaxy cluster Abell 1314 is located in Ursa Major at at distance of approximately 460 million light years from earth. It hosts large-scale radio emission that was caused by its merger with another cluster. Non-thermal radio emission detected with the LOFAR telescope is shown in red and pink, and thermal X-ray emission detected with the Chandra telescope is shown in gray, overlaid on an optical image.
Credit: Amanda Wilber/LOFAR Surveys Team
The nearby spiral galaxy M106 seen in an optical image, with LOFAR radio emission overlaid. The bright radio structures in the centre of the galaxy are not actually true spiral arms, but are believed to be the result of activity from the galaxy's central supermassive black hole.
Credit: Cyril Tasse and the LOFAR surveys team.
This image shows M51, also known as the Whirlpool Galaxy. It is 15-35 million light years from Earth and around 60,000 light years in diameter. At the centre of the spiral galaxy there sits a supermassive black hole. With the LOFAR data (yellow and red hues), we can see that the spiral galaxy and its companion are interacting because there is a bridge of emission joining them.
Credit: Sean Mooney/LOFAR Surveys Team/Digitized Sky Survey
Photos: Feaspb/shutterstock.com