Ergoregion instability of ultracompact astrophysical objects

  title={Ergoregion instability of ultracompact astrophysical objects},
  author={Vitor Cardoso and Paolo Pani and Mariano Cadoni and Marco Cavagli{\`a}},
  journal={Physical Review D},
Most of the properties of black holes can be mimicked by horizonless compact objects such as gravastars and boson stars. We show that these ultracompact objects develop a strong ergoregion instability when rapidly spinning. Instability time scales can be of the order of 0.1 seconds to 1 week for objects with mass $M=1\ensuremath{-}{10}^{6}{M}_{\ensuremath{\bigodot}}$ and angular momentum $Jg0.4{M}^{2}$. This provides a strong indication that ultracompact objects with large rotation are black… 
Ergoregion instability in rotating gravastars
The ergoregion instability is known to affect very compact objects that rotate very rapidly and do not possess a horizon. We present here a detailed analysis on the relevance of the ergoregion
Ergoregion instability of exotic compact objects: Electromagnetic and gravitational perturbations and the role of absorption
Spinning horizonless compact objects may be unstable against an ``ergoregion instability.'' We investigate this mechanism for electromagnetic perturbations of ultracompact Kerr-like objects with a
Instability of hyper-compact Kerr-like objects
Viable alternatives to astrophysical black holes include hyper-compact objects without horizon, such as gravastars, boson stars, wormholes and superspinars. The authors have recently shown that
Exotic Compact Objects and How to Quench their Ergoregion Instability
Gravitational-wave astronomy can give us access to the structure of black holes, potentially probing microscopic or even Planckian corrections at the horizon scale, as those predicted by some
How well can ultracompact bodies imitate black hole ringdowns
The ongoing observations of merging black holes by the instruments of the fledging gravitational wave astronomy has opened the way for testing the general relativistic Kerr black hole metric and, at
Black Hole Superradiance in Astrophysics
BHs are one of the most striking predictions of Einstein’s GR and, in fact, they are predicted by any relativistic theory of gravity [1]. Since Schmidt’s identification of the first quasar [2], large
Impact of multiple modes on the black-hole superradiant instability
Ultralight bosonic fields in the mass range $\sim (10^{-20}-10^{-11})\,{\rm eV}$ can trigger a superradiant instability that extracts energy and angular momentum from an astrophysical black hole with
The stochastic gravitational-wave background in the absence of horizons
Gravitational-wave astronomy has the potential to explore one of the deepest and most puzzling aspects of Einstein's theory: the existence of black holes. A plethora of ultracompact, horizonless
On gravitational-wave echoes from neutron-star binary coalescences
A tentative detection of gravitational-wave echoes in the post-merger signal of GW170817 has been recently claimed at $4.2\sigma$ significance level. It has been speculated that the signal might
Can accretion disk properties distinguish gravastars from black holes
Gravastars, hypothetic astrophysical objects, consisting of a dark energy condensate surrounded by a strongly correlated thin shell of anisotropic matter, have been proposed as an alternative to the


On the ergoregion instability
  • N. Comins, B. Schutz
  • Physics
    Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences
  • 1978
Rotating, ultra-compact stars in general relativity can have an ergo-region, in which all trajectories are dragged in the direction of the star’s rotation. The existence of the ergoregion leads to a
Gravitational-wave signature of an inspiral into a supermassive horizonless object
Event horizons are among the most intriguing of general relativity's predictions. Although on firm theoretical footing, direct indications of their existence have yet to be observed. With this
Black holes in astrophysics
This paper reviews the current status of black hole (BH) astrophysics, focusing on topics of interest to a physics audience. Astronomers have discovered dozens of compact objects with masses greater
w-mode instability of ultracompact relativistic stars
In this article we show that the mainly spacetime w modes may become unstable in a rotating ultracompact (R<3M) relativistic star. We provide results for the axial modes of a rotating star in the
Astrophysical violations of the Kerr bound as a possible signature of string theory
Abstract In 4D general relativity, the angular momentum of a black hole is limited by the Kerr bound. We suggest that in string theory, this bound can be breached and compact black-hole-like objects
Where are all the gravastars? Limits upon the gravastar model from accreting black holes
The gravastar model, which postulates a strongly correlated thin shell of anisotropic matter surrounding a region of anti-de Sitter space, has been proposed as an alternative to black holes. We
Supermassive black holes or boson stars? Hair counting with gravitational wave detectors
The evidence for supermassive Kerr black holes in galactic centers is strong and growing, but only the detection of gravitational waves will convincingly rule out other possibilities to explain the
Using LISA extreme-mass-ratio inspiral sources to test off-Kerr deviations in the geometry of massive black holes
Inspirals of stellar-mass compact objects (COs) into ~106M[sun] black holes are especially interesting sources of gravitational waves for the planned Laser Interferometer Space Antenna (LISA). The
Gravitational radiation from the r-mode instability
The instability in the r-modes of rotating neutron stars can (in principle) emit substantial amounts of gravitational radiation (GR) which might be detectable by LIGO and similar detectors. Estimates
Gravitational condensate stars: An alternative to black holes
A new solution for the endpoint of gravitational collapse is proposed. By extending the concept of Bose-Einstein condensation to gravitational systems, a cold, compact object with an interior de