Nicolas Sanchis-Gual

Lensing and dynamics of ultracompact bosonic stars

Spherically symmetric bosonic stars are one of the few examples of gravitating solitons that are known to form dynamically, via a classical process of (incomplete) gravitational collapse. As stationary solutions of the Einstein--Klein-Gordon or the Einstein--Proca theory, bosonic stars may also become sufficiently compact to develop light rings and hence mimic, in principle, gravitational-wave observational signatures of black holes (BHs). In this paper, we discuss how these horizonless ultra-compact objects (UCOs) are actually distinct from BHs, both phenomenologically and dynamically. In the electromagnetic channel, the light ring associated phenomenology reveals remarkable lensing patterns, quite distinct from a standard BH shadow, with an infinite number of Einstein rings accumulating in the vicinity of the light ring, both inside and outside the latter. The strong lensing region, moreover, can be considerably smaller than the shadow of a BH with a comparable mass. Dynamically, we investigate the fate of such UCOs under perturbations, via fully non-linear numerical simulations and observe that, in all cases, they decay into a Schwarzschild BH within a time scale of

Numerical evolutions of spherical Proca stars

\mathcal{O}(M)

Quasistationary solutions of self-gravitating scalar fields around collapsing stars

, where

Dynamical formation of a hairy black hole in a cavity from the decay of unstable solitons

M

Quasistationary solutions of scalar fields around collapsing self-interacting boson stars

is the mass of the bosonic star. Both these studies reinforce how difficult it is for horizonless UCOs to mimic BH phenomenology and dynamics, in all its aspects.

Completion of the universal I–Love–Q relations in compact stars including the mass

Vector boson stars, or

Quasistationary solutions of scalar fields around accreting black holes

\textit{Proca stars}

Comparison between the fCCZ4 and BSSN formulations of Einstein equations in spherical polar coordinates

, have been recently obtained as fully non-linear numerical solutions of the Einstein-(complex)-Proca system. These are self-gravitating, everywhere non-singular, horizonless Bose-Einstein condensates of a massive vector field, which resemble in many ways, but not all, their scalar cousins, the well-known (scalar)

Fully covariant and conformal formulation of the Z4 system compared to the BSSN formulation in spherical symmetry

\textit{boson stars}

Explosion and Final State of an Unstable Reissner-Nordström Black Hole

. In this paper we report fully-non linear numerical evolutions of Proca stars, focusing on the spherically symmetric case, with the goal of assessing their stability and the end-point of the evolution of the unstable stars. Previous results from linear perturbation theory indicate the separation between stable and unstable configurations occurs at the solution with maximal ADM mass. Our simulations confirm this result. Evolving numerically unstable solutions, we find, depending on the sign of the binding energy of the solution and on the perturbation, three different outcomes: