New York: American Institute of Physics, 1964. Wraps. First Edition. ,191-240,  pp. 4to. Gray paper wraps that are quite clean. Ex-library with small black library stamp on front cover and title page, no other markings. Very Good.
Soviet physicist Yakov B. Zel’dovich (1914-1987) proposed that active galaxies are powered by accretion disks around massive black holes at the center of galaxies, the currently accepted theory.