By NelmaS on Sex, 09/06/2017 - 22:31
Douglas O. Gough
Institute of Astronomy and Department of Applied Mathematics and Theoretical Physics University of Cambridge, UK
The Sun condensed from the interstellar medium 4.6 Gy ago, preserving, in the initial stages, a memory of the galactic vorticity and magnetic field. How it subsequently divested itself of almost all of that is one of the most important questions in asterophysics, yet remains far from being answered. Helioseismology has transformed our appreciation of the relevant issues, partly by eliminating many of the early conjectures regarding the Sun's present kinematical state. From our knowledge so gained of both the internal angular velocity and the density stratification, multipole moments of the external gravitational potential have been determined, providing a crucial test, in the weak-field limit, of General Relativity. A shear layer at the base of the convection zone, known as the tachocline, exists by dint of the dipolar vestige of the interior magnetic field, and has probably caused the magnetic axis to be inclined from the axis of rotation. I propose that the outcome induces a signature in the geomagnetic field, providing a precise estimate of the rotation rate of the Sun's radiative interior. These matters are no doubt of interest to astronomers who adopt the Sun as a prototype of cool main-sequence stars, but, more importantly in some minds, provide valuable information about the basic physics at play.
13 de junho de 2017 | 15:00
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto