On the dynamical bar-mode instability in spinning bosonic stars

Abstract

Spinning bosonic stars (SBSs) can form from the gravitational collapse of a dilute cloud of scalar/Proca particles with non-zero angular momentum. In a recent work we found that the scalar stars are transient due to a non-axisymmetric instability which triggers the loss of angular momentum. We further study the dynamical formation of SBSs using 3-dimensional numerical-relativity simulations of the Einstein-(massive, complex)Klein-Gordon system and of the Einstein-(complex)Proca system. We incorporate a quartic self-interaction potential in the scalar case to gauge its effect on the instability; we investigate (m=2) Proca stars to assess their stability; we attempt to relate the instability of SBSs to the growth rate of azimuthal density modes and the existence of a corotation point. We show that: the self-interaction potential can only delay the instability in scalar SBSs; m=2 Proca stars always migrate to the stable m=1 spheroidal family; unstable m=2 Proca stars and m=1 scalar boson stars exhibit a corotation point. This establishes a parallelism with rotating neutron stars affected by dynamical bar-mode instabilities. We compute the gravitational waves (GWs) emitted and investigate the detectability of the waveforms comparing the characteristic strain of the signal with the sensitivity curves of a variety of detectors, computing the signal-to-noise ratio. By assuming that the characteristic damping timescale of the bar-like deformation in SBSs is only set by GWs emission and not by viscosity (unlike in neutron stars), we find that the post-collapse emission could be orders of magnitude more energetic than that of the bar-mode instability itself. Our results indicate that GW observations of SBSs might be within the reach of future experiments, offering a potential means to establish the existence of such stars and to place tight constraints on the mass of the bosonic particle.

16 pages, 11 figures. A longer version of the abstract in the pdf

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• Impact of the wave-like nature of Proca stars on their gravitational-wave emission
• Self-interactions can stabilize excited boson stars
• Ultralight bosons for strong gravity applications from simple Standard Model extensions
• Extreme-mass-ratio inspirals into rotating boson stars: nonintegrability, chaos, and transient resonances
• Malaise and remedy of binary boson-star initial data
• Binary boson stars: Merger dynamics and formation of rotating remnant stars
• Gravitational waves from binary black hole mergers surrounded by scalar field clouds: Numerical simulations and observational implications
• Kerr black holes with synchronised axionic hair
• Head-on collisions of $\ell$-boson stars
• Proca-Higgs balls and stars in a UV completion for Proca self-interactions
• The multipolar structure of rotating boson stars
• Modeling gravitational waves from exotic compact objects
• Boson stars in Palatini $f(\mathcal{R})$ gravity
• Universal relations for rotating Boson Stars
• Self-interacting dipolar boson stars and their dynamics
• Gravitational-wave parameter inference with the Newman-Penrose scalar ${\psi }_4$
• Local Continuity of Angular Momentum and Noether Charge for Matter in General Relativity
• Numerical relativity surrogate models for exotic compact objects: the case of head-on mergers of equal-mass Proca stars
• Highly compact Proca stars with quartic self-interactions
• Assessing the stability of ultracompact spinning boson stars with nonlinear evolutions
• Boson star superradiance with spinning effects and in time domain
• Hair is complicated: Gravitational waves from stable and unstable boson-star mergers
• Rotating Boson Stars Using Finite Differences and Global Newton Methods
• Eccentric mergers of binary Proca stars
• Splitting the Gravitational Atom: Instabilities of Black Holes with Synchronized or Resonant Hair
• Slowly Rotating Boson Stars
• Impact of ultralight bosonic dark matter on the dynamical bar-mode instability of rotating neutron stars
• Soliton boson stars, Q-balls and the causal Buchdahl bound
• Ultralight bosonic dark matter in white dwarfs and potential observational consequences