German-born US astronomer whose most important work was
in the field of stellar structure and evolution. He greatly narrowed
the estimated range of mass that stars can have.
Schwarzschild was born in Potsdam, the son of astronomer Karl Schwarzschild.
After studying at Göttingen, he emigrated to the USA 1935. He was
professor at Columbia 1947-51 and at Princeton from 1951.
Schwarzschild worked out a quantity (ZHe) for the total mass density
of the elements heavier than helium, using the density of hydrogen as
one unit. The values of ZHe are smallest for old stars (0.003) and largest
for young stars (0.04), implying that the most recently formed stellar
objects were formed out of a medium of interstellar gas and dust that
was already enriched with heavy elements. These elements were probably
produced in stellar interiors and expelled by the oldest stars.
In 1938, Schwarzschild suggested that the star's deepest interior pulsates,
but that in the outermost regions the elements of gas do not all vibrate
in unison, causing a lag in the light curve by the observed amount.