Lightning can produce X-rays and gamma radiation. In the past, researchers thought that this phenomenon only lasted for a very short time, about one ten-thousandth of a second. However, the ionizing radiation of lightning appears to emit much longer than presumed. An afterglow of gamma radiation arises, which lasts up to 10,000 times longer. This is demonstrated for the first time by computer simulations by researchers from Centrum Wiskunde & Informatica (CWI) in Amsterdam. Their article “TGF afterglows: a new radiation mechanism from thunderstorms” has been published in Geophysical Review Letters. This discovery can provide more insight into how lightning develops.