Stars reside in galaxies, which are some of the most beautiful objects in the Universe. Galactic structure, dynamics and evolution are largely governed by the mutual gravitational attraction between the many stars and dark matter particles within them. The talk will begin with an elementary introduction to the physics of galaxies, leading to a mathematical formulation analogous to the kinetic theory of gases and plasmas. It is remarkable that the simply-stated theoretical framework allows description of the wide variety of observed galactic forms as many-body, self-gravitating structures. Two outstanding problems will be briefly discussed: (a) Formation of Elliptical galaxies; (b) Spiral Structure of Disc galaxies.
Seshadri Sridhar is a theoretical astrophysicist who uses nonlinear dynamics, fluid dynamics, kinetic theory of gases and plasma physics to explore problems in galactic astronomy. He got his PhD from the Indian Institute of Science and he was a postdoctoral fellow at Caltech and the Canadian Institute for Theoretical Astrophysics, after which he joined the Inter-University Centre for Astronomy and Astrophysics as faculty before joining RRI. His work on magnetohydrodynamic turbulence made a fundamental advance in the study of the anisotropic nature of the turbulent cascade of energy. Using many-body kinetic theory, he formulated the theoretical framework for following the evolution of black-hole star clusters. The highly suppressed dynamical friction experienced by a globular clusters in the cores of dwarf galaxies was explained by him in terms of the progressive drop-off in the number and strength of the available orbital resonances. His most recent work addresses the long-standing problem of the spiral structure of disc galaxies, predicting the suppression of dissipation in galactic scars which enables the renewal of new spiral density waves.