Oscillation and Instabilities of Relativistic Stars

Kokkotas, Kostas D.; Andersson, Nils

doi:10.1007/978-88-470-2101-3_9

Cited by 7 publications

(7 citation statements)

References 55 publications

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“…This suppression does appear to be a general property of relativistic fluid modes, especially relativistic pressure modes, as this phenomenon has also been found in other models [49,50,51,52,53,54,38,39].…”

Section: Wave Equation and Solutionssupporting

confidence: 73%

When black holes collide: Probing the interior composition by the spectrum of ringdown modes and emitted gravitational waves

2017

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The merger of colliding black holes (BHs) should lead to the production of ringdown or quasinormal modes (QNMs), which may very well be sensitive to the state of the interior. We put this idea to the test with a recent proposal that the interior of a BH consists of a bound state of highly excited, long, closed, interacting strings; figuratively, a collapsed polymer. We show, using scalar perturbations for simplicity, that such BHs do indeed have a distinct signature in their QNM spectrum: A new class of modes whose frequencies are parametrically lower than the lowest-frequency mode of a classical BH and whose damping times are parametrically longer. The reason for the appearance of the new modes is that our model contains another scale, the string length, which is parametrically larger than the Planck length. This distinction between the collapsed-polymer model and general-relativistic BHs could be made with gravitationalwave observations and offers a means for potentially measuring the strength of the coupling in string theory. For example, GW150914 already allows us to probe the strength of the string coupling near the regime which is predicted by the unification of the gravitational and gauge-theory couplings. We also derive bounds on the amplitude of the collapsed-polymer QNMs that can be placed by current and future gravitational-wave observations.

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Section: Wave Equation and Solutionssupporting

confidence: 73%

When black holes collide: Probing the interior composition by the spectrum of ringdown modes and emitted gravitational waves

2017

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“…Moreover, we consider only the dominant quadrupolar emission (l ¼ 2) here as higher-order modes (l > 2) will be subdominant [41,42] and also will occur at a higher frequency where the detectors lose sensitivity [43]. Hence, GWs associated with the excitation of pulsation modes (f modes) are short-lived signals, which can be expressed in the time domain as [18,44] hðtÞ ¼ h 0 e −t=τ gw sinð2πν gw tÞ:…”

Section: Signal Modelmentioning

confidence: 99%

“…Here, we are looking for the frequency of a GW signal emitted by an f-mode oscillation during a glitch that is related to the mean density of the NS [17,44,46]. These relations are found from the solution of the nonradial perturbations equation of a nonrotating star in general relativity (GR) or using the Cowling approximation [47,[81][82][83][84][85][86][87].…”

Section: Appendix: Comparison Of F -Mode Frequenciesmentioning

confidence: 99%

Prospects for detecting and localizing short-duration transient gravitational waves from glitching neutron stars without electromagnetic counterparts

et al. 2022

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Neutron stars are known to show accelerated spin-up of their rotational frequency called a glitch. Highly magnetized rotating neutron stars (pulsars) are frequently observed by radio telescopes (and in other frequencies), where the glitch is observed as irregular arrival times of pulses which are otherwise very regular. A glitch in an isolated neutron star can excite the fundamental (f)-mode oscillations which can lead to gravitational wave generation. This gravitational wave signal associated with stellar fluid oscillations has a damping time of 10-200 ms and occurs at the frequency range between 2.2-2.8 kHz for the equation of state and mass range considered in this work, which is within the detectable range of the current generation of ground-based detectors. Electromagnetic observations of pulsars (and hence pulsar glitches) require the pulsar to be oriented so that the jet is pointed toward the detector, but this is not a requirement for gravitational wave emission which is more isotropic and not jetlike. Hence, gravitational wave observations have the potential to uncover nearby neutron stars where the jet is not pointed towards the Earth. In this work, we study the prospects of finding glitching neutron stars using a generic all-sky search for short-duration gravitational wave transients. The analysis covers the high-frequency range from 1-4 kHz of LIGO-Virgo detectors for signals up to a few seconds. We set upper limits for the third observing run of the LIGO-Virgo detectors and present the prospects for upcoming observing runs of LIGO, Virgo, KAGRA, and LIGO India. We find the detectable glitch size will be around 10 −5 Hz for the fifth observing run for pulsars with spin frequencies and distances comparable to the Vela pulsar. We also present the prospects of localizing the direction in the sky of these sources with gravitational waves alone, which can facilitate electromagnetic follow-up. We find that for the five detector configuration, the localization capability for a glitch size of 10 −5 Hz is around 132 deg 2 at 1σ confidence for 50% of events with distance and spin frequency as that of Vela.

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“…Non-radial oscillation of non rotating stars emits GW as long as they have non zero quadrupolar moments, i.e, the perturbation associated with l ≥ 2 is not null. The energy is expected to be released, mostly, through excitation of a few of these quasi-normal modes and in general, the strongest emission occurs for quadrupolar modes, corresponding to l = 2 [63]. Hence, we will focus our attention on this case.…”

Section: Non-radial Oscillationsmentioning

confidence: 99%

Hybrid stars with sequential phase transitions: the emergence of the g$_2$ mode

Rodriguez,

Ranea-Sandoval,

Mariani

et al. 2020

Preprint

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Neutron stars are the densest objects in the Universe, with M ∼ 1.4M and R ∼ 12 km, and the equation of state associated to their internal composition is still unknown. The extreme conditions to which matter is subjected inside neutron stars could lead to a phase transition in their inner cores, giving rise to a hybrid compact object. The observation of 2M binary pulsars (PSR J1614-2230, PSR J0343+0432 and PSR J0740+6620) strongly constraints theoretical models of the equation of state. Moreover, the detection of gravitational waves emitted during the binary neutron star merger, GW170817, and its electromagnetic counterpart, GRB170817A, impose additional constraints on the tidal deformability. In this work, we investigate hybrid stars with sequential phase transitions hadron-quark-quark in their cores. For the outer core, we use modern hadronic equations of state. For the inner core we employ the constant speed of sound parametrization for quark matter. We analyze more than 3000 hybrid equations of state, taking into account the recent observational constraints from neutron stars. The effects of hadron-quark-quark phase transitions on the normal oscillation modes f and g, are studied under the Cowling relativistic approximation. Our results show that a second quark-quark phase transition produces a noticeable change on the oscillation frequency for both f and g modes and, also, giving rise to a new g 2 mode. We discuss the observational implications of our results associated to the gravitational waves detection and the possibility of detecting hints of sequential phase transitions and the associated g 2 mode.

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Oscillation and Instabilities of Relativistic Stars

Abstract: Abstract. In this short review we discuss the relevance of ongoing research into stellar oscillations and associated instabilities for the detection of gravitational waves and the future field of "gravitational-wave astronomy".

Cited by 7 publications

References 55 publications

When black holes collide: Probing the interior composition by the spectrum of ringdown modes and emitted gravitational waves

When black holes collide: Probing the interior composition by the spectrum of ringdown modes and emitted gravitational waves

Prospects for detecting and localizing short-duration transient gravitational waves from glitching neutron stars without electromagnetic counterparts

Hybrid stars with sequential phase transitions: the emergence of the g$_2$ mode

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