Astronomers have a lot in common with forensic scientists. They infer from traces the events that might have led to the formation of these traces. They take photographs and look at what is visible of these events in order to then also be able to capture their invisible parts. Very much remains invisible in the universe: Black holes, dark matter or dark energy, which we all see only through their effects, are certainly the most prominent. But also magnetic fields play an important role. They provide the framework in which charged particles move in galaxies. For example, when clusters…