Karl Schwarzschild

German astrophysicist

• Born: October 9, 1873; Frankfurt am Main, Germany
• Died: May 11, 1916; Potsdam, Germany

Karl Schwarzschild developed a new use for photography as a tool for measuring the brightness of stars, particularly variable objects. He was the first to develop a solution for Albert Einstein’s general relativity field equations, dealing with gravity around a star of such intensity that it becomes a black hole.

Primary fields: Astronomy; physics

Specialties: Observational astronomy; theoretical astronomy; astrophysics

Early Life

Karl Schwarzschild was the eldest of six children. His father, a prosperous businessman in Frankfurt, encouraged his early interest in science, particularly astronomy. He was the first of his family to be interested in science; indeed, he wrote and published his first two astronomical papers, on the topic of double-star orbits, when he was only sixteen. While in school, he was introduced to J. Epstein, a mathematician with a private observatory. From Epstein’s son, Schwarzschild learned to make and use a telescope and studied advanced mathematics and celestial mechanics. After local education at the primary and secondary level, he spent two years at the University of Strasbourg and then two more years at the University of Munich. He received his doctorate from that university in 1896, graduating summa cum laude. His doctoral thesis was on the application of the theory of stable configurations in rotating bodies, developed by Henri Poincaré, to investigations of tidal deformation in satellites and the validity of Pierre-Simon Laplace’s theory for the origin of the solar system. He also invented a multislit interferometer for measuring the separation of double stars.

Life’s Work

Schwarzschild was interested in observational astronomy. In the early 1890s, he developed the use of photography (later called photographic photometry) to measure the apparent magnitude of stars using a photographic plate to substitute for the human eye at the telescope. Using his new method of measuring the image densities on the plates, he was able to establish the magnitude of 367 stars; he used those results to secure a teaching position at the University of Munich. In all, he worked on thirty-five hundred stellar objects of magnitude greater than 7.5, at the same time showing conclusively that there was a vast difference between visual (with the unaided eye) and photographic magnitude or brightness, a difference later known as the star’s color index. His results also led him to suggest that periodic variable stars behaved as they did, going through a regular cycle of maximum and minimum brightness, because of periodic temperature changes. In turn, this hypothesis led to further work on Cepheid variables by English astronomer Arthur Eddington.

From 1896 to 1899, Schwarzschild worked as an assistant at the Kuffner Observatory in Vienna. After some time spent lecturing and writing, he received an associate professorship in 1901 from the University of Göttingen. A year later, he became a professor of astronomy there as well as the director of its observatory. In 1909, he succeeded Hermann Vogel as the director of the Astrophysical Observatory in Potsdam.

Schwarzschild worked extensively in theoretical astronomy and in subjects as diverse as orbital mechanics, the curvature of space throughout the known universe, stellar energy production, and the surface structures of the sun. In 1900, he suggested that the geometry of space did not necessarily have to conform to Euclidean geometry, in which two parallel lines are forever parallel and the sum of interior angles of a triangle is always 180 degrees. Light rays from a star hitting the Earth’s orbit at two widely separated points form an overextended triangle. By measuring the interior angles of such a hypothetical structure, he attempted to determine the curvature of space, since he knew that, if the angles added up to more or less than 180 degrees, he would be dealing with non-Euclidean space. He concluded, from his experimental results, that if space were curved, it had an extremely large radius of curvature, so large as to be unnoticeable in as small a region as the solar system.

In 1906, Schwarzschild worked diligently on a paper showing that a star should not be considered as a simple gas held together by its own gravity. Thermodynamic properties, particularly concerning the transfer of heat inside the stellar surface by both convection and radiation, had to be present. To deal effectively with this situation, he invented the concept of radiative equilibrium in astrophysics, a balance of the energy flowing inward and outward to help maintain the star’s stability. He showed mathematically how radiative processes would be important in conveying heat in stellar atmospheres and how energy could be transferred at and near the sun’s surface. Many of his ideas were stimulated by his observation of the total solar eclipse in 1905, an event he photographed with a newly devised instrument, one forming spectrograms from an objective prism at the eyepiece of the telescope. This instrument allowed him to derive information on the chemical composition of various areas at differing depths in the sun’s atmosphere.

Among the topics to which he contributed was the field of stellar statistics, which studies large numbers of stars and their associated data. The methods and techniques he developed are now standard in graduate stellar astronomy courses. He designed, as a new tool for analysis, a spectrographic objective that provided a reliable means of determining a star’s radial velocity, the speed and direction in which it is moving. Many new contributions to geometric optics stemmed from this fertile period.

Schwarzschild volunteered for military service in 1914, at the start of World War I, first manning a weather station in Belgium, then transferring to France for the job of calculating the trajectories for long-range cannon shells. Craving action, he managed to transfer again, to Russia. While in Russia in 1916, he heard of Albert Einstein’s new general theory of relativity. As a result, Schwarzschild wrote two papers on the theory, both published that year.

Schwarzschild provided a solution—the first to be found—to the complex partial differential equations fundamental to the theory’s mathematical basis. He solved the Einstein equation for the exterior space-time of a spherical nonrotating body, thereby predicting the formation of black holes. The theoretical study of black holes and the continuing search for them has become an important field in modern astronomy, particularly since they can be used to solve some of the most fundamental problems of stellar, galactic, and cosmological astronomy.

While in Russia, Schwarzschild contracted pemphigus, an incurable metabolic disease of the skin. He was disabled and living solely at home in 1916 when he died. For his service in the war effort, he was awarded an Iron Cross. In 1960, he was honored by the Berlin Academy, which named him the greatest German astronomer of the preceding century.

Impact

As an astronomer and theoretician, Schwarzschild ach-ieved many great things in his chosen field, despite his short life. His practical skill was demonstrated in the innovative instruments he designed and built, including astrophotographic tools, spectral analysis instruments, and designs in geometrical optics. With his exceptional mathematical ability, he contributed greatly to theoretical astronomy in subjects including celestial mechanics, stellar physics, solar dynamics, thermodynamics of stellar interiors, and applications of the theory of relativity, all of which remain important fields of research in modern astronomy.

Schwarzschild attached great importance to lecturing and writing on popular astronomy. He attempted to make difficult subjects in physics and astronomy more lucid, presenting pictures with words that the average nonscientist could understand. He was equally at home with his scientific associates, ready to discuss and extend any conjecture or idea. As a theoretical astrophysicist, he was one of the great promoters of Niels Bohr’s 1913 theory of atomic spectra, a theory that he believed would solve most of the analytic problems of stellar spectral analysis. While on his deathbed, Schwarzschild finished a famous paper on that subject, in which he developed the rules of quantization. That work, developed independently by Arnold Sommerfeld, provided for the theory of the Stark effect and the quantum theory of molecular structure.

Among those whom Schwarzschild inspired was his son Martin Schwarzschild (1912–97), who later followed in his footsteps. The younger Schwarzschild later contributed his own great work in astronomy, primarily on the theory of stellar structure and evolutionary dynamics.

Bibliography

Kaufmann, William J., III. Black Holes and Warped Spacetime. San Francisco: Freeman, 1979. Print. Discusses the general theory of relativity and its consequences, particularly in terms of star deaths. Extensive section on the Schwarzschild radius and its importance in forming black holes, altering the space around the star. Written for general readers, with a comprehensive nonmathematical treatment.

Melia, Fulvio. The Edge of Infinity: Supermassive Black Holes in the Universe. New York: Cambridge UP, 2003. Print. Includes information about Schwarzschild’s discoveries.

Talcott, Richard. “What Makes a Black Hole Tick?” Astronomy 33.10 (2005): 80–81. Print. A series of diagrams explaining the composition of black holes for nonspecialists.