## Answers

Chandrasekhar’s working life can be divided into distinct periods, each period usually concluding with a book or monograph on the topic: he studied stellar structure, including the theory of white dwarfs, during the years 1929 to 1939 (summarized in his 1939 book “An Introduction to the Study of Stellar Structure”); he focussed on stellar dynamics from 1939 to 1943 (his book “Principles of Stellar Dynamics” was published in 1942); he concentrated on the theory of radiative transfer and thequantum theory of the negative ion of hydrogen from 1943 to 1950 (represented by another book, “Radiative Transfer”, published in 1950); he worked on hydrodynamic and hydromagnetic stability from 1950 to 1961 (his book “Hydrodynamic and Hydromagnetic Stability” was published in 1961); he studied the equilibrium and the stability of ellipsoidal figures of equilibrium, and also general relativity, during the 1960s (summarized in the book “Ellipsoidal Figures of Equilibrium” in 1968); during the period 1971 to 1983 he studied the mathematical theory of black holes (as described in his 1983 book “The Mathematical Theory of Black Holes”); and during the late 1980s he worked on the theory of colliding gravitational waves.