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.


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