Spherical accretion of collisional gas in modified gravity I: self-similar solutions and a new cosmological hydrodynamical code

TL;DR

This paper investigates self-similar solutions of spherical accretion in a modified gravity model and introduces a new hydrodynamical code, confirming its accuracy against theoretical predictions and setting the stage for more complex future simulations.

Contribution

It presents the first analysis of self-similar solutions in a specific modified gravity model and develops a new hydrodynamical code validated against these solutions.

Findings

Self-similar solutions in the MG model closely match Einstein-de Sitter results.

The new hydrodynamical code ExaHyPE 2 accurately reproduces theoretical predictions.

Modified gravity effects are significant but do not alter the core self-similar behavior.

Abstract

The spherical collapse scenario has great importance in cosmology since it captures several crucial aspects of structure formation. The presence of self-similar solutions in the Einstein-de Sitter (EdS) model greatly simplifies its analysis, making it a powerful tool to gain valuable insights into the real and more complicated physical processes involved in galaxy formation. While there has been a large body of research to incorporate various additional physical processes into spherical collapse, the effect of modified gravity (MG) models, which are popular alternatives to the $\Lambda CDM$ paradigm to explain the cosmic acceleration, is still not well understood in this scenario. In this paper, we study the spherical accretion of collisional gas in a particular MG model, which is a rare case that also admits self-similar solutions. The model displays interesting behaviours caused by the enhanced gravity and a screening mechanism. Despite the strong effects of MG, we find that its self-similar solution agrees well with that of the EdS model. These results are used to assess a new cosmological hydrodynamical code for spherical collapse simulations introduced here, which is based on the hyperbolic partial differential equation engine ExaHyPE 2. Its good agreement with the theoretical predictions confirms the reliability of this code in modelling astrophysical processes in spherical collapse. We will use this code to study the evolution of gas in more realistic MG models in future work.