The year 1915 brought a discovery that was to lead to many controversial discussions in the years that followed. It showed that there must obviously be extremely dense states of matter in the cosmos, for which there was not even an explanation at the time. This discovery was made by Walter Sydney Adams (1876–1956) at the Mt. Wilson Observatory and concerned the color of Sirius’ companion—it was not red, as assumed, but blue-white, which means that this star must have a similarly high effective temperature as Sirius itself.