Search for H2 cloudlets in our backyard

TL;DR

This study searches for small molecular hydrogen clouds near the Sun using gamma-ray and UV data, setting upper limits on their local density and total mass, which informs dark matter composition models.

Contribution

It introduces a novel method combining gamma-ray and UV observations to constrain the abundance of small H2 clouds in the Solar neighborhood.

Findings

Upper limit on local H2 cloud density: n < 2.2 x 10^-11 AU^-3

Constraints on total mass range: 0.05-30 solar masses

No direct detection, but significant upper limits established.

Abstract

Several observational lines of evidence imply that a fraction of the dark matter in the Galaxy may be comprised of small cold clouds of molecular hydrogen. Such objects are difficult to detect because of their small size and low temperature, but they can reveal themselves with gamma radiation arising in interactions between such clouds and cosmic rays or as dark shadows cast on the optical, UV and X-ray sky background. In our work we use the data of Fermi LAT 4FGL-DR4 catalogue of gamma-ray sources together with the data of GALEX UV All-Sky Survey to search for small dark clouds of molecular hydrogen in the Solar neighbourhood. This approach allows us to put an upper limit on the local concentration of such objects: $n < 2.2 \times 10^{-11} {\mathrm{AU}^{-3}}$. Constraints (upper limits) on the total amount of matter in this form bound to the Sun strongly depend on the radial profile of the clouds' distribution and reside in $0.05-30~M_{\odot}$ mass range.