Karl Schwarzschild
In 1909 Karl Schwarzschild succeeded Vogel as director. In addition
to Astronomy, Schwarzchild was also active in the field of Theoretical Physics. He had
come from Göttingen where he had been made a full professor at the age of 28 and
was also the director of Gauss's old observatory there.
Unfortunately he contracted a fatal disease on the Russian front during the war and died in Potsdam in May 1916, not before producing the work for which he is most famous i.e finding the first exact solution to Einstein's Field Equations - for the case of a gravitational field of a point mass in empty space - the Schwarzschild Solution (which therefore describes the field around a static black hole).
At almost the same time, while severely unwell, he had also produced important work in quantum theory. He was an early champion and great promoter of Nils Bohr's new quantum theory and had, in 1900, suggested that the geometry of space was not Euclidean.
Solar theory was one of his interests at Potsdam and in 1906 he explained solar limb darkening as being due to the fact that when we look at the center of the Sun, we are seeing into deeper and hotter layers. He took part in Potsdam's expedition to Tenerife in 1911 to study Halley's comet and studied the density and structure of its tail.