In astrophysics, asteroseismology is the science of determining the interior structure of stars based upon their pulsation behavior. While physically more complicated, the behavior of pulsating stars is analogous to the sounds emitted by a guitar strings of different lengths, compositions, and tensions, or by bells of different sizes and weights. Asteroseismology is like trying to figure out the structure of a musical instrument based on the sounds it makes. It is very similar to seismology of the Earth -- using earthquakes to study the interior structure of our planet -- except that the Sun and stars are entirely gaseous objects.

Variable stars that pulsate have what are called "normal modes" of oscillation. These normal modes can be 3D-symmetric, "radial" modes where the star expands and contracts with the frequency of the mode. Or they may be "non-radial" or "sectoral" modes where different sections of the star move in and out in a regular fashion. The modes observed in a given star depend upon two things:

  1. The interior properties of the star
  2. The spherical harmonic indices (l,m,n) of the pulsation mode.

Early theoretical work was conducted on the pulsations of variable stars by astrophysicists and mathematicians like Sir Arthur Eddington, Paul Ledoux, and Chaim Pekeris in the first half of the twentieth century. They studied the behavior of simple stellar models (like spherical polytropes) perturbed into one of these normal modes (like striking a bell). Later, other astrophysicists expanded upon these ideas to include more realistic physics, like better equations of state, and the effects of rotation and convection.

Our star, The Sun is known to pulsate in thousands of independent pulsation modes, most with frequencies of a few millihertz (or periods of about five minutes). By studying these pulsations, we have learned a lot about the structure of the Sun to very high precision. Several other kinds of stars are also known to pulsate, including white dwarfs and delta Scuti stars.

The purpose of asteroseismology (beyond fulfilling our curiosity) is to study the interiors of stars, even stars that are thousands of light years away. Since the pulsations are dependent upon the interior conditions, they can tell us about how old the star is, what its chemical composition is, and the dynamical behavior of the interior. Studying individual pulsating stars can teach us things about stars in general, and by extension, about the universe as a whole.

I note that the spelling is asteroseismology, rather than astroseismology. The former is the IAU-defined standard, because it implies the study of an individual star (aster is Greek for "star").

Log in or registerto write something here or to contact authors.