Very large yet faint galaxies have been found where no one would have expected them – in the middle of a giant galaxy cluster. Heidelberg astronomers discovered the extremely-low density galaxies, known as ultra-diffuse galaxies, a find that is “both remarkable and puzzling”, states Dr Thorsten Lisker. The research work was carried out by Carolin Wittmann in Dr Lisker’s team at the Centre for Astronomy of Heidelberg University (ZAH). The results have been published in the Monthly Notices of the Royal Astronomical Society