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arXiv · 2304.12018

Birth of baby universes from gravitational collapse in a modified-gravity scenario

Andreu Masó-Ferrando·Nicolas Sanchis-Gual·José A. Font·Gonzalo J. Olmo
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Abstract

We consider equilibrium models of spherical boson stars in Palatini $f(\mathcal{R})=\mathcal{R}+\xi \mathcal{R}^2$ gravity and study their collapse when perturbed. The Einstein-Klein-Gordon system is solved using a recently established correspondence in an Einstein frame representation. We find that, in that frame, the endpoint is a nonrotating black hole surrounded by a quasi-stationary cloud of scalar field. However, the dynamics in the $f(\mathcal{R})$ frame is dramatically different. The innermost region of the collapsing object exhibits the formation of a finite-size, exponentially-expanding $\textit{ baby universe}$ connected with the outer (parent) universe via a minimal area surface (a throat or umbilical cord). Our simulations indicate that this surface is at all times hidden inside a horizon, causally disconnecting the baby universe from observers above the horizon. The implications of our findings in other areas of gravitational physics are also discussed.

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Andreu Masó-Ferrando, Nicolas Sanchis-Gual, José A. Font, Gonzalo J. Olmo. 2023-04-24. Birth of baby universes from gravitational collapse in a modified-gravity scenario. https://doi.org/10.1088/1475-7516%2F2023%2F06%2F028

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