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arXiv · 2105.00530

A stabilization mechanism for excited fermion-boson stars

Fabrizio Di Giovanni·Saeed Fakhry·Nicolas Sanchis-Gual·Juan Carlos Degollado·José A. Font
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Abstract

We study numerically the nonlinear stability of {\it excited} fermion-boson stars in spherical symmetry. Such compound hypothetical stars, composed by fermions and bosons, are gravitationally bound, regular, and static configurations described within the coupled Einstein-Klein-Gordon-Euler theoretical framework. The excited configurations are characterized by the presence in the radial profile of the (complex, massive) scalar field -- the bosonic piece -- of at least one node across the star. The dynamical emergence of one such configuration from the accretion of a cloud of scalar field onto an already-formed neutron star, was numerically revealed in our previous investigation. Prompted by that finding we construct here equilibrium configurations of excited fermion-boson stars and study their stability properties using numerical-relativity simulations. In addition, we also analyze their dynamical formation from generic, constraint-satisfying initial data. Contrary to purely boson stars in the excited state, which are known to be generically unstable, our study reveals the appearance of a cooperative stabilization mechanism between the fermionic and bosonic constituents of those excited-state mixed stars. While similar examples of stabilization mechanisms have been recently discussed in the context of $\ell-$boson stars and multi-field, multi-frequency boson stars, our results seem to indicate that the stabilization mechanism is a purely gravitational effect and does not depend on the type of matter of the companion star.

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Fabrizio Di Giovanni, Saeed Fakhry, Nicolas Sanchis-Gual, Juan Carlos Degollado, José A. Font. 2021-05-02. A stabilization mechanism for excited fermion-boson stars. https://doi.org/10.1088/1361-6382%2Fac1b45

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