Gravitational Waves as a New Probe for Astronomy and Fundamental Physics

A topical collection in Universe (ISSN 2218-1997). This collection belongs to the section "Gravitation".

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Collection Editor
1. Institut UTINAM, CNRS UMR 6213, Observatoire de Besançon, Université de Franche Compté, 41 bis ave. de l'Observatoire, BP 1615, 25010 Besançon, France
2. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking GU5 6NT, UK
Interests: high-energy astronomy: gravitational waves and their electromagnetic counterparts; gamma-ray bursts and their progenitors; ultrahigh energy cosmic rays; cosmology: dark energy and dark matter models; quantum condensates and coherent states in cosmology; relation between dark energy and inflation; signatures of dark sector physics on the evolution of large scale structure of the Universe; Fundamental particle physics: foundation of quantum mechanics and its relation with quantum gravity, quantum cosmology, QCD and colour glass condensate method, and their applications to new physics

Topical Collection Information

Dear Colleagues,

It is our pleasure to invite you to contribute to a Universe Topical Collection on “Gravitational Waves as a New Probe for Astronomy and Fundamental Physics”. The aim is to gather a collection of contributions—theoretical, observational or methodology, original research or review—which highlight the current state-of-the-art research in observation and modelling of gravitational waves sources. Investigation of accompanying electromagnetic and particle emissions is specially appreciated.

Rationale: Pioneering detection of GRAVITATIONAL WAVES (GW) from tens of merging stellar mass objects by the LIGO and Virgo observatories has opened up a new era in understanding the universe and provided a new far-reaching tool for exploring matter and cosmos in the most extreme conditions. So far, these observations have proven the existence of black holes with a horizon as predicted by the Einstein general relativity, confirmed propagation of massless spin 2 gravitons with the speed of light, and stringently constrained several alternative models of gravity. In particular, coincident observation of GW170817 and a short gamma-ray burst have proven that they are produced by merging binary neutron stars and/or black hole and neutron star, constrained their properties, provided an independent measurement of Hubble constant, etc.

These discoveries have brought surprises, too. For instance, the existence of black holes with masses much larger than ~30M cannot be explained by models of star formation, and compact objects in the mass gap, that is, ~2.5M<M<~5M⊙, found through their GW are not predicted by theories and are not observed in electromagnetic bands. Therefore, more theoretical and observational investigations are necessary.

In the near future, new ground- and space-based GW observatories will improve detection threshold and position resolution. Moreover, their pass band will be extended to lower frequencies, suitable for detection of GW from mergers of supermassive binary black holes, collapse of massive stars by supernova explosion, and phase transitions in the early universe. Detection of background GW and its fluctuations should extend our view of the Universe much farther than what is achievable with the cosmic microwave background. On the other hand, GW170817 event has demonstrated the value of multi-probe follow ups of GW sources. They are crucial for extensive exploration of underlying processes.

Dr. Houri Ziaeepour
Collection Editor

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Keywords

  • Gravitational waves
  • Gravitational wave background
  • Electromagnetic counterpart of gravitational waves
  • Binary merger
  • Black hole
  • Neutron star
  • Early universe
  • Phase transitions in early universe
  • Cosmic microwave background
  • Cosmology

Published Papers (6 papers)

2024

Jump to: 2023, 2022

11 pages, 255 KiB  
Article
Probing the Dark Universe with Gravitational Waves
by Antonio Enea Romano
Universe 2024, 10(11), 426; https://doi.org/10.3390/universe10110426 - 15 Nov 2024
Viewed by 330
Abstract
Gravitational waves (GWs) are expected to interact with dark energy and dark matter, affecting their propagation on cosmological scales. To model this interaction, we derive a gauge-invariant effective equation and action valid for all GW polarizations. This is achieved by encoding the effects [...] Read more.
Gravitational waves (GWs) are expected to interact with dark energy and dark matter, affecting their propagation on cosmological scales. To model this interaction, we derive a gauge-invariant effective equation and action valid for all GW polarizations. This is achieved by encoding the effects of GW interactions at different orders of perturbation into a polarization-, frequency-, and time-dependent effective speed. The invariance of perturbations under time-dependent conformal transformations and the gauge invariance of GWs allow us to derive the unitary gauge effective action in any conformally related frame, thereby clarifying the relationship between the Einstein and Jordan frames. Tests of the polarization and frequency dependencies in the propagation time and luminosity distance of different GW polarizations allow us to probe the dark Universe, which acts as an effective medium, modeled by the GW effective speed. Full article
18 pages, 766 KiB  
Review
Time-Delay Interferometry: The Key Technique in Data Pre-Processing Analysis of Space-Based Gravitational Waves
by Pan-Pan Wang and Cheng-Gang Shao
Universe 2024, 10(10), 398; https://doi.org/10.3390/universe10100398 - 16 Oct 2024
Viewed by 663
Abstract
Space gravitational wave detection primarily focuses on the rich wave sources corresponding to the millihertz frequency band, which provide key information for studying the fundamental physics of cosmology and astrophysics. However, gravitational wave signals are extremely weak, and any noise during the detection [...] Read more.
Space gravitational wave detection primarily focuses on the rich wave sources corresponding to the millihertz frequency band, which provide key information for studying the fundamental physics of cosmology and astrophysics. However, gravitational wave signals are extremely weak, and any noise during the detection process could potentially overwhelm the gravitational wave signals. Therefore, data pre-processing is necessary to suppress the main noise sources. Among the various noise sources, laser phase noise is dominant, approximately seven orders of magnitude larger in strength than typical gravitational wave signals, and requires suppression using time-delay interferometry (TDI) techniques, which involve combining raw data with time delays. This paper will be based on the basic principles of TDI to present methods for obtaining multi-type TDI combinations, including algebraic methods for solving indeterminate equations and geometric methods for symbolic search. Furthermore, the applicability of TDI under actual operating conditions will be considered, such as the arm locking in conjunction with the TDI algorithm. Finally, the sensitivity functions for different types of TDI combinations will be provided, which can be used to evaluate the signal-to-noise ratio (SNRs) of different TDI combinations. Full article
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2023

Jump to: 2024, 2022

14 pages, 332 KiB  
Review
The Distributional Stress–Energy Quadrupole and Gravitational Waves
by Jonathan Gratus and Spyridon Talaganis
Universe 2023, 9(12), 518; https://doi.org/10.3390/universe9120518 - 15 Dec 2023
Viewed by 1359
Abstract
In this overview, we discuss the (Schwartz) distributional stress–energy quadrupole and show it is a source of gravitational waves. We provide an explicit formula for the metric of linearised gravity in the case of a background Minkowski spacetime. We compare and contrast the [...] Read more.
In this overview, we discuss the (Schwartz) distributional stress–energy quadrupole and show it is a source of gravitational waves. We provide an explicit formula for the metric of linearised gravity in the case of a background Minkowski spacetime. We compare and contrast the two different representations for quadrupoles taken by Dixon and Ellis, present the formula for the dynamics of the quadrupole moments, and determine the number of free components. We review other approaches to the dynamics of quadrupoles, comparing our results. Full article
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2022

Jump to: 2024, 2023

15 pages, 329 KiB  
Article
Properties and Patterns of Polarized Gravitational Waves
by Bahram Mashhoon and Sohrab Rahvar
Universe 2023, 9(1), 6; https://doi.org/10.3390/universe9010006 - 21 Dec 2022
Cited by 2 | Viewed by 1380
Abstract
We discuss the polarization of gravitational radiation within the standard framework of linearized general relativity. The recent experimental discovery of gravitational waves provides the impetus to revisit the implications of the spin-rotation-gravity coupling for polarized gravitational radiation; therefore, we consider the coupling of [...] Read more.
We discuss the polarization of gravitational radiation within the standard framework of linearized general relativity. The recent experimental discovery of gravitational waves provides the impetus to revisit the implications of the spin-rotation-gravity coupling for polarized gravitational radiation; therefore, we consider the coupling of the helicity of gravitational waves to the rotation of an observer or the gravitomagnetic field of a rotating astronomical source. Observational possibilities regarding polarization-dependent effects in connection with future gravitational wave detectors are briefly explored. Full article
19 pages, 641 KiB  
Article
Thermodynamics of Hot Neutron Stars and Universal Relations
by Pavlos Laskos-Patkos, Polychronis S. Koliogiannis, Alkiviadis Kanakis-Pegios and Charalampos C. Moustakidis
Universe 2022, 8(8), 395; https://doi.org/10.3390/universe8080395 - 27 Jul 2022
Cited by 4 | Viewed by 2513
Abstract
Over the last few years, the detection of gravitational waves from binary neutron star systems has rekindled our hopes for a deeper understanding of the unknown nature of ultradense matter. In particular, gravitational wave constraints on the tidal deformability of a neutron star [...] Read more.
Over the last few years, the detection of gravitational waves from binary neutron star systems has rekindled our hopes for a deeper understanding of the unknown nature of ultradense matter. In particular, gravitational wave constraints on the tidal deformability of a neutron star can be translated into constraints on several neutron star properties using a set of universal relations. Apart from binary neutron star mergers, supernova explosions are also important candidates for the detection of multimessenger signals. Such observations may allow us to impose significant constraints on the binding energy of neutron stars. The purpose of the present study is twofold. Firstly, we investigate the agreement of finite temperature equations of state with established universal relations. Secondly, we examine the possible existence of a universal relation between the binding energy and the dimensionless tidal deformability, which are the bulk properties connected to the most promising sources for multimessenger signals. We find that hot equations of state are not always compatible with accepted universal relations. Therefore, the use of such expressions for probing general relativity or imposing constraints on the structure of neutron stars would be inconclusive (when thermal effects are present). Additionally, we show that the binding energy and the dimensionless tidal deformability exhibit a universal trend at least for moderate neutron star masses. The latter allows us to set bounds on the binding energy of a 1.4 M neutron star using data from the GW170817 event. Finally, we provide a relation between the compactness, the binding energy and the dimensionless tidal deformability of a neutron star that is accurate for cold and hot isentropic equations of state. Full article
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16 pages, 1054 KiB  
Article
The Equation of State of Neutron-Rich Matter at Fourth Order of Chiral Effective Field Theory and the Radius of a Medium-Mass Neutron Star
by Francesca Sammarruca and Randy Millerson
Universe 2022, 8(2), 133; https://doi.org/10.3390/universe8020133 - 19 Feb 2022
Cited by 9 | Viewed by 2397
Abstract
We report neutron star predictions based on our most recent equations of state. These are derived from chiral effective field theory, which allows for a systematic development of nuclear forces, order by order. We utilize high-quality two-nucleon interactions and include all three-nucleon forces [...] Read more.
We report neutron star predictions based on our most recent equations of state. These are derived from chiral effective field theory, which allows for a systematic development of nuclear forces, order by order. We utilize high-quality two-nucleon interactions and include all three-nucleon forces up to fourth order in the chiral expansion. Our ab initio predictions are restricted to the domain of applicability of chiral effective field theory. However, stellar matter in the interior of neutron stars can be up to several times denser than normal nuclear matter at saturation, and its composition is essentially unknown. Following established practices, we extend our microscopic predictions to higher densities matching piecewise polytropes. The radius of the average-size neutron star, about 1.4 solar masses, is sensitive to the pressure at normal densities, and thus it is suitable to constrain ab initio theories of the equation of state. For this reason, we focus on the radius of medium-mass stars. We compare our results with other theoretical predictions and recent constraints. Full article
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