In 1915 he began a study of the companion of Sirius and found that despite a size only slightly larger than the Earth, the surface of the star was brighter per unit area than the Sun and it was about as massive.
I 1915 begyndte han at studere Sirius' følgestjerne og fandt, at til trods for at den kun var lidt større end Jorden, var stjernens overflade lysere per arealenhed end Solen, og at den var næsten lige så massiv som den.