What is the amount of baryonic dark matter in galaxies?

Abstract

In this paper, we re-evaluate the estimates of dust mass in galaxies and demonstrate that current dust models are incomplete and based on a priori assumptions. These models suffer from a circularity problem and account for only a small portion of dust, specifically submicron-sized grains. They overlook larger dust particles and other macroscopic bodies, despite observational evidence supporting their existence. This evidence includes the observed (sub)millimetre excess in dust emission spectra and the power-law size distribution with a differential size index $\gamma \approx 3.5-4.0$, which has been measured for large particles and compact bodies across diverse environments. Examples of these large particles include large dust grains and meteoroids detected by satellites, near-Earth objects colliding with Earth, fragments in the Main Asteroid Belt and the Kuiper Belt, interstellar ’Oumuamua-like objects, and exoplanets. As a result, dust-type baryonic dark matter may be more abundant throughout the galaxy by one order of magnitude or even more than previously assumed, with a significant portion of its mass concentrated in large compact bodies. Additionally, black holes may contribute significantly to the total mass of baryonic dark matter. Consequently, current galaxy models do not provide reliable estimates of baryonic mass in galaxies. Clearly, a substantially larger amount of baryonic dark matter in galaxies would have major implications for theories of galaxy dynamics and evolution.