Obituary: Professor Martin Schwarzschild

Martin Schwarzschild, eminent theoretical and observational astronomer, was a world leader in the theory of stellar structure and evolution and of galactic structure.

Besides writing other important papers on theoretical and observational astronomy, he pioneered the use of space telescopes to obtain sharp photographs from above the Earth's fluctuating atmosphere. His versatility, transparent personal integrity, enthusiasm for ideas and skill in communication made him a very effective advisor on scientific matters, both national and international. He was a worthy son to Karl Schwarzschild, a father he hardly remembered.

Schwarzschild's early life in some ways typified that of many other German citizens of Jewish stock. His father's family had for centuries lived in the Frankfurt Judengasse. Following emancipation in the 19th century, they entered with enthusiasm into Germany's economic, intellectual and cultural life.

Karl Schwarzschild was a man of genius, who can fairly be described as the father of astrophysics: in just 20-odd years of active research, he introduced many fundamental ideas and methods now commonplace among astronomers. But come 1914, although past 40, and in spite of his distaste for militarism, as a German Jew he felt morally obliged to volunteer, following the German army first into Belgium with a scientific unit, and subsequently onto the Eastern Front. In 1916 he contracted a painful skin disease which killed him, but not before he had written his last scientific papers, including one on ballistics, and the two that are probably his most famous, constructing exact solutions of Einstein's general relativistic field equations.

The young Martin's faint recollections of his father, and the high regard with which his memory was held both in his childhood home at Gottingen and in the astronomical world must have acted as an inspiration rather than an impediment. But his graduation in physics and astronomy coincided with the political triumph of the Nazis, for whom his father's patriotism counted for little. Both Martin Schwarzschild and his elder sister Agathe (subsequently Professor of Classics at Dunedin in New Zealand) were forced into exile. His younger brother, who remained with their "Aryan" mother in Gottingen, was ultimately driven to suicide.

After a year as Research Fellow at Oslo and a brief visit to Britain, Schwarzschild emigrated to the United States in 1937, becoming a citizen in 1942, and serving as a lieutenant with army intelligence. After the war he returned at first to his position as Assistant Professor at Columbia University's Rutherford Observatory. It showed commendable farsightedness on the part of Princeton that when appointing Lyman Spitzer as Professor of Astronomy and successor to H.N. Russell as Director of the Observatory, they agreed to Spitzer's request that Schwarzschild also be appointed. Their fields of work both overlapped and complemented each other; together, they built up a strong graduate school in theoretical and observational astronomy.

Schwarzschild is probably best known for his seminal contributions to our understanding of stellar structure and evolution. He was quick to recognise the power of the newly developed electronic computers to deal with the rather intractable mathematics, and in particular to incorporate the complicated details of the input physics. The culmination of a long series of studies was a landmark paper written jointly with Fred Hoyle, "On the Evolution of Type 2 Stars", published in 1955, which showed convincingly how the evolution due to nuclear processing of initially homogeneous stars would lead naturally to the red giant sequence and the associated short- period pulsating stars, as observed in the globular clusters. But Schwarzschild would not be satisfied with just the output from the computer: he would always want to understand the reasons for numerical predictions in qualitative physical terms. His monograph Structure and Evolution of the Stars (1958) has been a standard text for generations of students of all ages.

The same combination of physical insight, computational expertise and an insistence on precision in detail shows in his other main theoretical interest - the dynamics of galactic structure, especially of elliptical galaxies. His skilled use of the computer for the construction of the orbits of individual stars, and the final use of these orbits for synthesizing the self- consistent gravitational field, triggered an explosion of activity in this area. His other theoretical work includes a seminal paper on the heating of the solar corona by shock waves emanating from the turbulent convection zone just below the surface, and a pioneering paper with Martin Kruskal on the instabilities that bedevil laboratory plasmas, for example in potential thermonuclear devices.

Schwarzschild also made many important contributions to observational astronomy. Together with his wife Barbara, he drew attention to the striking differences in chemical composition between respectively high- and low- velocity dwarf stars, crucial to our understanding of the chemical evolution of galaxies. In another seminal paper, he pointed out that optical measurements of the Andromeda galaxy pointed not to rigid rotation but rather to a constant rotational velocity, subsequently confirmed by the radio astronomers as omnipresent in disc-like galaxies, such as our own Milky Way.

However, Schwarzschild's major contribution to observational astronomy was probably through his pioneering use of space telescopes for precise imaging of the Sun, planets and stellar systems. His "Stratoscope I" 12- inch solar telescope, balloon-borne up to 80,000 feet, was the first instrument to obtain sharp photographs of the solar surface. The subsequent "Stratoscope II" three-foot telescope gave similar first-of-a-kind results on the outer planets and galactic nuclei. These experiments were harbingers of the now familiar Hubble Space Telescope, which is set to revolutionise optical astronomy.

It is probably no coincidence that Martin Schwarzschild's heart condition should have become terminal just ten days after the sudden death of Lyman Spitzer, his close colleague and friend for over half a century. Certainly, those many who have enjoyed and profited from the warm hospitality of Princeton University Observatory will feel that an era has truly come to an end.

Leon Mestel

Martin Schwarzschild, astronomer: born Potsdam, Germany 31 May 1912; Research Fellow, Institute of Astrophysics, Oslo 1936-37; Research Fellow, Harvard University Observatory 1937-40; Lecturer, Columbia University 1940-44, Assistant Professor 1944-7; Professor, Princeton University 1947- 50, Higgins Professor of Astronomy 1950-79; Vice-President, International Astronomical Union 1964-70; Vice-President, American Astronomical Society 1967-69, President 1970-72; married 1945 Barbara Cherry; died Langhorne, Pennsylvania 10 April 1997.