The Universe as an Inside-Out Star

TL;DR

This paper explores the use of acoustic oscillations in astrophysics, comparing helioseismology and CMB studies, highlighting their similarities and differences in understanding spherical surfaces.

Contribution

It provides a pedagogical comparison of the physics and methodologies of helioseismology and CMB analysis, emphasizing their commonalities and differences.

Findings

Both fields utilize spherical harmonics in their analysis.

They share similar physics principles despite different applications.

The paper clarifies fundamental distinctions between the two research areas.

Abstract

Acoustic modes can be used to study the physics of the interior of a cavity, and this is especially useful when the inside region is inaccessible. Many astrophysicists use such sound waves as an essential tool in their research. Here we focus on two separate sub-fields in which oscillations on the surface of a sphere are studied -- Helioseismology and CMBology -- the surface being either the solar or cosmic photosphere. Both research areas use the language of spherical harmonics, as well as sharing many close similarities in the underlying physics. However, there are also many fundamental differences, which we explain in this pedagogical article.