# Dynamical formation and stability of fermion-boson stars

**Authors:** Fabrizio Di Giovanni, Saeed Fakhry, Nicolas Sanchis-Gual, Juan Carlos Degollado, José A. Font  
**arXiv:** [2006.08583](https://arxiv.org/abs/2006.08583)  
**Date:** 2020-06-15  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2006.08583v1/

## Key points

- Study investigates formation and stability of fermion-boson stars
- Structures composed of fermions and scalar particles
- EKGE system used to solve the coupled equations
- Focus on scenario involving neutron star and accreting cloud of scalar field
- Initial scalar field expelled through gravitational cooling, leading to equilibrium configuration
- Evidence of node in scalar field for large positive coupling constant
- Suggests fermionic core may stabilize configurations with nodes in bosonic sector
- Provides insights into dynamical formation and stability of fermion-boson stars

## Summary

In the study titled "Dynamical formation and stability of fermion-boson stars," authors Fabrizio Di Giovanni, Saeed Fakhry, Nicolas Sanchis-Gual, Juan Carlos Degollado, and José A. Font investigate the formation and stability of gravitationally bound structures known as fermion-boson stars. These structures are composed of fermions (particles with half-integer spin) and scalar particles (bosons) and are obtained by solving the coupled Einstein-Klein-Gordon-Euler (EKGE) system. The researchers focus on a specific scenario in which fermion-boson stars may form. They numerically solve the EKGE system under the simplifying assumption of spherical symmetry. Their simulations involve an existing neutron star surrounded by an accreting cloud of a massive and complex scalar field. The results reveal interesting dynamics within the system as part of the initial scalar field is expelled through gravitational cooling. Gradually, the system settles into an equilibrium configuration that is asymptotically consistent with a static solution of the EKGE system. Furthermore, for large positive values of the coupling constant in the self-interaction term of the scalar-field potential, there is evidence of a node in the scalar field. This suggests that a fermionic core may play a role in stabilizing configurations with nodes in the bosonic sector, similar to what occurs in purely boson stars where both ground state and first excited state coexist. Overall, this study provides insights into <kw>dynamical formation</kw> and <kw>stability</kw> of <kw>fermion-boson stars</kw>. By numerically solving the EKGE system under simplified assumptions, the authors shed light on how these gravitationally bound structures can arise from an already existing neutron star surrounded by an accreting cloud of scalar particles. The presence of nodes in the scalar field and the potential stabilizing effect of a fermionic core add to our understanding of these intriguing astrophysical objects.