How is lightning initiated in thunderclouds? This is difficult to answer - how do you measure electric fields inside large, dangerously charged clouds? It was discovered, more or less by coincidence, that cosmic rays provide .
This schematic illustrates the creation of a runaway galaxy. In the first panel, an "intruder" spiral galaxy approaches a galaxy cluster center, where a compact elliptical galaxy (cE) already revolves around a massive central elliptical galaxy.
Best Of European Space Agency Photos - Herchel's Image Of Andromeda Galaxy The European Space Agency's Herschel Space Observatory took this infrared image of the Andromeda Galaxy, showing rings of dust that trace gaseous reservoirs where new stars are