Dark matter and alternative recipes for the missing mass

TL;DR

This paper reviews the role of dark matter in galaxies, discusses its elusive nature, and explores alternative theories like modified gravity and MOND as potential replacements for dark matter.

Contribution

It analyzes dark matter distribution in galaxies and evaluates alternative theories such as modified gravity and MOND to explain galactic dynamics without dark matter.

Findings

Dark matter content varies with galaxy mass and size.

Modified gravity theories can fit galactic observations.

MOND offers a viable alternative to dark matter in some cases.

Abstract

Within the standard cosmological scenario the Universe is found to be filled by obscure components (dark matter and dark energy) for ~95% of its energy budget. In particular, almost all the matter content in the Universe is given by dark matter, which dominates the mass budget and drives the dynamics of galaxies and clusters of galaxies. Unfortunately, dark matter and dark energy have not been detected and no direct or indirected observations have allowed to prove their existence and amount. For this reason, some authors have suggested that a modification of Einstein Relativity or the change of the Newton's dynamics law (within a relativistic and classical framework, respectively) could allow to replace these unobserved components. We will start discussing the role of dark matter in the early-type galaxies, mainly in their central regions, investigating how its content changes as a function of the mass and the size of each galaxy and few considerations about the stellar Initial mass function have been made. In the second part of the paper we have described, as examples, some ways to overcome the dark matter hypothesis, by fitting to the observations the modified dynamics coming out from general relativistic extended theories and the MOdyfied Newtonian dynamics (MOND).