Nordita Astrophysics Seminars

From terrestrial to astrophysical oceanography through a short wave analysis

by Anthony Bonfils

Albano 3: 6228 - Mega (22 seats) (Albano Building 3)

Albano 3: 6228 - Mega (22 seats)

Albano Building 3


A white dwarf may accrete material (principally hydrogen and helium) from a companion star, increasing the density and temperature and possibly giving rise to runaway nuclear burning. The resulting energy is accompanied by ejection of material called novae ejecta, which can contain a significant amount of heavier elements, such as carbon, nitrogen, and oxygen, presumably entrained and brought upward from the deeper layers of the white dwarf. This process, which is the presumed to be the primary source of carbon and oxygen in the universe, is poorly understood. Rosner and others [1] proposed that the Miles instability of surface waves forced by a shear flow is responsible for the mixing of elements at the surface of the white dwarf. The Miles instability originated in physical oceanography as a mechanism for the growth of wind waves [2,3]. In this talk, I will explain how to generalize that instability to astrophysical settings. Next, I will take advantage of the large scales in astrophysical flows to perform a short wave analysis and obtain a general asymptotic formula for the growth rate of the Miles instability [4]. Along the way, I will discuss the potential relevance of another oceanographic instability — the so-called rippling instability [5] —  for this astrophysical puzzle.

[1] R. Rosner et al., Astrophys. J., 562:L177, 2001.

[2] J. W. Miles, J. Fluid Mech., 3:185-204, 1957.

[3] A. F. Bonfils, D. Mitra, W. Moon, and J. S. Wettlaufer, J. Fluid Mech., 944:A8, 2022.

[4] A. F. Bonfils, D. Mitra, W. Moon, and J. S. Wettlaufer, arXiv:2211.02942.

[5] W. R. Young and C. L. Wolfe, J. Fluid Mech., 739:276-307, 2014.