Does the Sun have a Dark Disk?

TL;DR

This paper investigates the possibility of a non-luminous dark disk or ring around the Sun by analyzing discrepancies in solar oblateness measurements, gravitational effects on Mercury, and circumsolar dust evidence, aiming to constrain hidden mass.

Contribution

It develops methods to use observational data to limit the mass of potential dark structures near the Sun and discusses how future studies can refine these constraints.

Findings

Discrepancies in solar quadrupole moment assessments suggest possible non-luminous mass.

Evidence of a circumsolar dust ring within Mercury's orbit.

Proposed observational strategies to detect and constrain dark matter components near the Sun.

Abstract

The Sun is not quite a perfect sphere, and its oblateness, thought to be induced through its rotation, has been measured using optical observations of its radius. Its gravitational quadrupole moment can then be deduced using solar models, or through helioseismology, and it can also be determined from measurements of its gravitational effects on Mercury's orbit. The various assessments do not appear to agree, with the most complete and precise orbital assessments being in slight excess of other determinations. This may speak to the existence of a non-luminous disk or ring, where we also note evidence for a circumsolar dust ring within Mercury's orbit from the Solar TErrestrial RElations Observatory (STEREO) mission. Historically, too, a protoplanetary disk may have been key to reconciling the Sun's metallicity with its neutrino yield. The distribution of the non-luminous mass within Mercury's orbit can modify the relative size of the optical and orbital quadrupole moments in different ways. We develop how we can use these findings to limit the mass of a dark disk, ring, or halo in the immediate vicinity of the Sun, and we note how future observational studies of the inner solar system can not only refine these constraints but also help to identify and to assess the mass of its dark-matter component.