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Present and Future of Gravitational Wave Astronomy
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Present and Future of Gravitational Wave Astronomy

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (10 January 2022) | Viewed by 56409

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Dr. Gabriele Vajente

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Guest Editor
LIGO Laboratory, California Institute of Technology, Pasadena, CA 91125, USA
Interests: gravitational waves; gravitational wave detection; laser metrology; coatings

Special Issue Information

Dear Colleagues,

The first detection on Earth of a gravitational wave signal from the coalescence of a binary black hole system [1] in 2015 opened a new era in astronomy, allowing the scientific community to observe the Universe with a new form of radiation for the first time. More than five years later, many more gravitational wave signals have been detected [2,3], including the first binary neutron star coalescence in coincidence with a gamma ray burst and a kilonova observation [4,5].

The field of gravitational wave astronomy is rapidly evolving, making it difficult to keep up with the pace of new detector designs, discoveries, and astrophysical results.

This Special Issue is therefore intended as a review of the current status and future directions of the field from the point of view of detector technology, data analysis, and the astrophysical implications of these discoveries.

Rather than focusing on presenting new results, the articles collected in this issue will serve as a reference and an introduction to the field. This Special Issue will include reviews of the basic properties of gravitational wave signals; the detectors that are currently operating and the main sources of noise that limit their sensitivity; planned upgrades of the detectors in the short and long terms; spaceborne detectors; data analysis of the gravitational wave detector output, focusing on the main classes of detected and expected signals; implications of the current and future discoveries on our understanding of astrophysics and cosmology.

Similar reviews and introductory books already exist in the literature [6,7,8,9], and this Special Issue will continue in the tradition of these works by updating the material presented therein and bridging the gaps between detector science, data analysis, and their astrophysical implications.

References:

[1] Abbott, B. P.; et al. [LIGO Scientific Collaboration and Virgo Collaboration]. Observation of Gravitational Waves from a Binary Black Hole Merger. Phys. Rev. Lett. 2016, 116, 061102.

[2] Abbott, B. P.; et al. [LIGO Scientific Collaboration and Virgo Collaboration]. GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs. Phys. Rev. X. 2019, 9, 031040.

[3] Abbott, R.; et al. [LIGO Scientific Collaboration and Virgo Collaboration]. GWTC-2: Compact Binary Coalescences Observed by LIGO and Virgo During the First Half of the Third Observing Run. 2020. arXiv:2010.14527[gr-qc].

[4] Abbott, B. P.; et al. [LIGO Scientific Collaboration and Virgo Collaboration]. GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral. Phys. Rev. Lett. 2017, 119, 161101.

[5] Abbott, B. P.; et al. Multi-messenger Observations of a Binary Neutron Star Merger. Astrophys. J. Lett. 2017, 848, L12.

[6] Bassan, M. Advanced Interferometers and the Search for Gravitational Waves. Springer: London, UK; 2014. ISBN 978-3-319-03791-2; doi:10.1007/978-3-319-03792-9.

[7] Reitze, D. H.; Saulson, P.; Grote, H. Advanced Interferometric Gravitational-Wave Detectors. World Scientific: Singapore, 2016; doi:10.1142/10181.

[8] Vajente, G.; Gustafson, E.; Reitze, D. H. Precision interferometry for gravitational wave detection: Current status and future trends. Adv. At. Mol. Opt. Phys. 2019, 68, 75. doi:10.1016/bs.aamop.2019.04.002.

[9] Maggiore, M. Gravitational Waves: Volume 2: Astrophysics and Cosmology. Oxford University Press: Oxford, UK, 2018. ISBN-13: 9780198570899; doi:10.1093/oso/9780198570899.001.0001.

Dr. Gabriele Vajente
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Galaxies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • gravitation wave astrophysics
  • gravitational wave detectors
  • high-precision laser metrology
  • gravitational wave cosmology

Published Papers (15 papers)

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Editorial

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5 pages, 10077 KiB  
Editorial
Present and Future of Gravitational Wave Astronomy
by Gabriele Vajente
Galaxies 2022, 10(4), 91; https://doi.org/10.3390/galaxies10040091 - 19 Aug 2022
Cited by 2 | Viewed by 1743
Abstract
Gravitational waves (GW) are propagating perturbations of the space-time metric, generated by time-varying mass distributions [...] Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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Research

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10 pages, 682 KiB  
Article
Gravitational Waves from a Core-Collapse Supernova: Perspectives with Detectors in the Late 2020s and Early 2030s
by Marek Szczepańczyk and Michele Zanolin
Galaxies 2022, 10(3), 70; https://doi.org/10.3390/galaxies10030070 - 23 May 2022
Cited by 6 | Viewed by 2099
Abstract
We studied the detectability and reconstruction of gravitational waves from core-collapse supernova multidimensional models using simulated data from detectors predicted to operate in the late 2020s and early 2030s. We found that the detection range will improve by a factor of around two [...] Read more.
We studied the detectability and reconstruction of gravitational waves from core-collapse supernova multidimensional models using simulated data from detectors predicted to operate in the late 2020s and early 2030s. We found that the detection range will improve by a factor of around two with respect to the second-generation gravitational-wave detectors, and the sky localization will significantly improve. We analyzed the reconstruction accuracy for the lower frequency and higher frequency portion of supernova signals with a 250 Hz cutoff. Since the waveform’s peak frequencies are usually at high frequencies, the gravitational-wave signals in this frequency band were reconstructed more accurately. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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36 pages, 53972 KiB  
Article
Research Facilities for Europe’s Next Generation Gravitational-Wave Detector Einstein Telescope
by Sibilla Di Pace, Valentina Mangano, Lorenzo Pierini, Amirsajjad Rezaei, Jan-Simon Hennig, Margot Hennig, Daniela Pascucci, Annalisa Allocca, Iara Tosta e Melo, Vishnu G. Nair, Philippe Orban, Ameer Sider, Shahar Shani-Kadmiel and Joris van Heijningen
Galaxies 2022, 10(3), 65; https://doi.org/10.3390/galaxies10030065 - 28 Apr 2022
Cited by 15 | Viewed by 4563
Abstract
The Einstein Telescope is Europe’s next generation gravitational-wave detector. To develop all necessary technology, four research facilities have emerged across Europe: The Amaldi Research Center (ARC) in Rome (Italy), ETpathfinder in Maastricht (The Netherlands), SarGrav in the Sos Enattos mines on Sardinia (Italy) [...] Read more.
The Einstein Telescope is Europe’s next generation gravitational-wave detector. To develop all necessary technology, four research facilities have emerged across Europe: The Amaldi Research Center (ARC) in Rome (Italy), ETpathfinder in Maastricht (The Netherlands), SarGrav in the Sos Enattos mines on Sardinia (Italy) and E-TEST in Liége (Belgium) and its surroundings. The ARC pursues the investigation of a large cryostat, equipped with dedicated low-vibration cooling lines, to test full-scale cryogenic payloads. The installation will be gradual and interlaced with the payload development. ETpathfinder aims to provide a low-noise facility that allows the testing of full interferometer configurations and the interplay of their subsystems in an ET-like environment. ETpathfinder will focus amongst others on cryogenic technologies, silicon mirrors, lasers and optics at 1550 and 2090 nm and advanced quantum noise reduction schemes. The SarGrav laboratory has a surface lab and an underground operation. On the surface, the Archimedes experiment investigates the interaction of vacuum fluctuations with gravity and is developing (tilt) sensor technology for the Einstein Telescope. In an underground laboratory, seismic characterisation campaigns are undertaken for the Sardinian site characterisation. Lastly, the Einstein Telecope Euregio meuse-rhine Site & Technology (E-TEST) is a single cryogenic suspension of an ET-sized silicon mirror. Additionally, E-TEST investigates the Belgian–Dutch–German border region that is the other candidate site for Einstein Telescope using boreholes and seismic arrays and hydrogeological characterisation. In this article, we describe the Einstein Telescope, the low-frequency part of its science case and the four research facilities. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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26 pages, 5912 KiB  
Article
The Current Status and Future Prospects of KAGRA, the Large-Scale Cryogenic Gravitational Wave Telescope Built in the Kamioka Underground
by Homare Abe, Tomotada Akutsu, Masaki Ando, Akito Araya, Naoki Aritomi, Hideki Asada, Yoichi Aso, Sangwook Bae, Rishabh Bajpai, Kipp Cannon, Zhoujian Cao, Eleonora Capocasa, Man Leong Chan, Dan Chen, Yi-Ru Chen, Marc Eisenmann, Raffaele Flaminio, Heather K. Fong, Yuta Fujikawa, Yuya Fujimoto, I. Putu Wira Hadiputrawan, Sadakazu Haino, Wenbiao Han, Kazuhiro Hayama, Yoshiaki Himemoto, Naoatsu Hirata, Chiaki Hirose, Tsung-Chieh Ho, Bin-Hua Hsieh, He-Feng Hsieh, Chia-Hsuan Hsiung, Hsiang-Yu Huang, Panwei Huang, Yao-Chin Huang, Yun-Jing Huang, David C. Y. Hui, Kohei Inayoshi, Yuki Inoue, Yousuke Itoh, Pil-Jong Jung, Takaaki Kajita, Masahiro Kamiizumi, Nobuyuki Kanda, Takashi Kato, Chunglee Kim, Jaewan Kim, Young-Min Kim, Yuichiro Kobayashi, Kazunori Kohri, Keiko Kokeyama, Albert K. H. Kong, Naoki Koyama, Chihiro Kozakai, Jun’ya Kume, Sachiko Kuroyanagi, Kyujin Kwak, Eunsub Lee, Hyung Won Lee, Ray-Kuang Lee, Matteo Leonardi, Kwan-Lok Li, Pengbo Li, Lupin Chun-Che Lin, Chun-Yu Lin, En-Tzu Lin, Hong-Lin Lin, Guo-Chin Liu, Ling-Wei Luo, Miftahul Ma’arif, Yuta Michimura, Norikatsu Mio, Osamu Miyakawa, Kouseki Miyo, Shinji Miyoki, Nozomi Morisue, Kouji Nakamura, Hiroyuki Nakano, Masayuki Nakano, Tatsuya Narikawa, Lan Nguyen Quynh, Takumi Nishimoto, Atsushi Nishizawa, Yoshihisa Obayashi, Kwangmin Oh, Masatake Ohashi, Tomoya Ohashi, Masashi Ohkawa, Yoshihiro Okutani, Ken-ichi Oohara, Shoichi Oshino, Kuo-Chuan Pan, Alessandro Parisi, June Gyu Park, Fabián E. Peña Arellano, Surojit Saha, Kazuki Sakai, Takahiro Sawada, Yuichiro Sekiguchi, Lijing Shao, Yutaka Shikano, Hirotaka Shimizu, Katsuhiko Shimode, Hisaaki Shinkai, Ayaka Shoda, Kentaro Somiya, Inhyeok Song, Ryosuke Sugimoto, Jishnu Suresh, Takamasa Suzuki, Takanori Suzuki, Toshikazu Suzuki, Hideyuki Tagoshi, Hirotaka Takahashi, Ryutaro Takahashi, Hiroki Takeda, Mei Takeda, Atsushi Taruya, Takayuki Tomaru, Tomonobu Tomura, Lucia Trozzo, Terrence T. L. Tsang, Satoshi Tsuchida, Takuya Tsutsui, Darkhan Tuyenbayev, Nami Uchikata, Takashi Uchiyama, Tomoyuki Uehara, Koh Ueno, Takafumi Ushiba, Maurice H. P. M. van Putten, Tatsuki Washimi, Chien-Ming Wu, Hsun-Chung Wu, Tomohiro Yamada, Kazuhiro Yamamoto, Takahiro Yamamoto, Ryo Yamazaki, Shu-Wei Yeh, Jun’ichi Yokoyama, Takaaki Yokozawa, Hirotaka Yuzurihara, Simon Zeidler and Yuhang Zhaoadd Show full author list remove Hide full author list
Galaxies 2022, 10(3), 63; https://doi.org/10.3390/galaxies10030063 - 26 Apr 2022
Cited by 18 | Viewed by 5712
Abstract
KAGRA is a gravitational-wave (GW) detector constructed in Japan with two unique key features: It was constructed underground, and the test-mass mirrors are cooled to cryogenic temperatures. These features are not included in other kilometer-scale detectors but will be adopted in future detectors [...] Read more.
KAGRA is a gravitational-wave (GW) detector constructed in Japan with two unique key features: It was constructed underground, and the test-mass mirrors are cooled to cryogenic temperatures. These features are not included in other kilometer-scale detectors but will be adopted in future detectors such as the Einstein Telescope. KAGRA performed its first joint observation run with GEO600 in 2020. In this observation, the sensitivity of KAGRA to GWs was inferior to that of other kilometer-scale detectors such as LIGO and Virgo. However, further upgrades to the detector are ongoing to reach the sensitivity for detecting GWs in the next observation run, which is scheduled for 2022. In this article, the current situation, sensitivity, and future perspectives are reviewed. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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14 pages, 882 KiB  
Article
Toward Calibration of the Global Network of Gravitational Wave Detectors with Sub-Percent Absolute and Relative Accuracy
by Sudarshan Karki, Dripta Bhattacharjee and Richard L. Savage
Galaxies 2022, 10(2), 42; https://doi.org/10.3390/galaxies10020042 - 5 Mar 2022
Cited by 2 | Viewed by 2018
Abstract
The detection of gravitational-wave signals by the LIGO and Virgo observatories during the past few years has ushered us into the era of gravitational-wave astronomy, shifting our focus from detection to source parameter estimation. This has imposed stringent requirements on calibration in order [...] Read more.
The detection of gravitational-wave signals by the LIGO and Virgo observatories during the past few years has ushered us into the era of gravitational-wave astronomy, shifting our focus from detection to source parameter estimation. This has imposed stringent requirements on calibration in order to maximize the astrophysical information extracted from these detected signals. Current detectors rely on photon radiation pressure from auxiliary lasers to achieve required calibration accuracy. These photon calibrators have made significant improvements over the last few years, realizing fiducials displacements with sub-percent accuracy. This achieved accuracy is directly dependent on the laser power calibration. For the next observing campaign, scheduled to begin at the end of 2022, a new scheme is being implemented to achieve improved laser power calibration accuracy for all of the GW detectors in the global network. It is expected to significantly improve absolute and relative calibration accuracy for the entire network. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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15 pages, 706 KiB  
Article
Optimization of Design Parameters for Gravitational Wave Detector DECIGO Including Fundamental Noises
by Yuki Kawasaki, Ryuma Shimizu, Tomohiro Ishikawa, Koji Nagano, Shoki Iwaguchi, Izumi Watanabe, Bin Wu, Shuichiro Yokoyama and Seiji Kawamura
Galaxies 2022, 10(1), 25; https://doi.org/10.3390/galaxies10010025 - 1 Feb 2022
Cited by 7 | Viewed by 1928
Abstract
The DECi-hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector. DECIGO was originally designed to be sensitive enough to observe primordial GW background (PGW). However, due to the lowered upper limit of the PGW by the Planck observation, further improvement [...] Read more.
The DECi-hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector. DECIGO was originally designed to be sensitive enough to observe primordial GW background (PGW). However, due to the lowered upper limit of the PGW by the Planck observation, further improvement of the target sensitivity of DECIGO is required. In the previous studies, DECIGO’s parameters were optimized to maximize the signal-to-noise ratio (SNR) of the PGW to quantum noise including the effect of diffraction loss. To simulate the SNR more realistically, we optimize DECIGO’s parameters considering the GWs from double white dwarfs (DWDs) and the thermal noise of test masses. We consider two cases of the cutoff frequency of GWs from DWDs. In addition, we consider two kinds of thermal noise: thermal noise in a residual gas and internal thermal noise. To investigate how the mirror geometry affects the sensitivity, we calculate it by changing the mirror mass, keeping the mirror thickness, and vice versa. As a result, we obtained the optimums for the parameters that maximize the SNR that depends on the mirror radius. This result shows that a thick mirror with a large radius gives a good SNR and enables us to optimize the design of DECIGO based on the feasibility study of the mirror size in the future. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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19 pages, 2168 KiB  
Article
Seismic and Newtonian Noise in the GW Detectors
by Lucia Trozzo and Francesca Badaracco
Galaxies 2022, 10(1), 20; https://doi.org/10.3390/galaxies10010020 - 22 Jan 2022
Cited by 5 | Viewed by 3924
Abstract
Gravitational wave detectors aim to measure relative length variations of the order of ΔL/L≃10−21, or less. Thus, any mechanism that is able to reproduce such a tiny variation can, in principle, threaten the sensitivity of [...] Read more.
Gravitational wave detectors aim to measure relative length variations of the order of ΔL/L≃10−21, or less. Thus, any mechanism that is able to reproduce such a tiny variation can, in principle, threaten the sensitivity of these instruments, representing a source of noise. There are many examples of such noise, and seismic and Newtonian noise are among these and will be the subject of this review. Seismic noise is generated by the incessant ground vibration that characterizes Earth. Newtonian noise is instead produced by the tiny fluctuations of the Earth’s gravitational field. These fluctuations are generated by variations of air and soil density near the detector test masses. Soil density variations are produced by the same seismic waves comprising seismic noise. Thus, it makes sense to address these two sources of noise in the same review. An overview of seismic and Newtonian noise is presented, together with a review of the strategies adopted to mitigate them. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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Review

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22 pages, 1362 KiB  
Review
Cosmic Explorer: A Next-Generation Ground-Based Gravitational-Wave Observatory
by Evan D. Hall 
Galaxies 2022, 10(4), 90; https://doi.org/10.3390/galaxies10040090 - 18 Aug 2022
Cited by 18 | Viewed by 3130
Abstract
Cosmic Explorer is a concept for a new laser interferometric observatory in the United States to extend ground-based gravitational-wave astrophysics into the coming decades. Aiming to begin operation in the 2030s, Cosmic Explorer will extend current and future detector technologies to a 40 [...] Read more.
Cosmic Explorer is a concept for a new laser interferometric observatory in the United States to extend ground-based gravitational-wave astrophysics into the coming decades. Aiming to begin operation in the 2030s, Cosmic Explorer will extend current and future detector technologies to a 40 km interferometric baseline—ten times larger than the LIGO observatories. Operating as part of a global gravitational-wave observatory network, Cosmic Explorer will have a cosmological reach, detecting black holes and neutron stars back to the times of earliest star formation. It will observe nearby binary collisions with enough precision to reveal details of the dynamics of the ultradense matter in neutron stars and to test the general-relativistic model of black holes. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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64 pages, 3915 KiB  
Review
Compact Binary Coalescences: Astrophysical Processes and Lessons Learned
by Mario Spera, Alessandro Alberto Trani and Mattia Mencagli
Galaxies 2022, 10(4), 76; https://doi.org/10.3390/galaxies10040076 - 25 Jun 2022
Cited by 25 | Viewed by 3173
Abstract
On 11 February 2016, the LIGO and Virgo scientific collaborations announced the first direct detection of gravitational waves, a signal caught by the LIGO interferometers on 14 September 2015, and produced by the coalescence of two stellar-mass black holes. The discovery represented the [...] Read more.
On 11 February 2016, the LIGO and Virgo scientific collaborations announced the first direct detection of gravitational waves, a signal caught by the LIGO interferometers on 14 September 2015, and produced by the coalescence of two stellar-mass black holes. The discovery represented the beginning of an entirely new way to investigate the Universe. The latest gravitational-wave catalog by LIGO, Virgo and KAGRA brings the total number of gravitational-wave events to 90, and the count is expected to significantly increase in the next years, when additional ground-based and space-born interferometers will be operational. From the theoretical point of view, we have only fuzzy ideas about where the detected events came from, and the answers to most of the five Ws and How for the astrophysics of compact binary coalescences are still unknown. In this work, we review our current knowledge and uncertainties on the astrophysical processes behind merging compact-object binaries. Furthermore, we discuss the astrophysical lessons learned through the latest gravitational-wave detections, paying specific attention to the theoretical challenges coming from exceptional events (e.g., GW190521 and GW190814). Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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36 pages, 1466 KiB  
Review
Status and Perspectives of Continuous Gravitational Wave Searches
by Ornella Juliana Piccinni
Galaxies 2022, 10(3), 72; https://doi.org/10.3390/galaxies10030072 - 25 May 2022
Cited by 27 | Viewed by 3418
Abstract
The birth of gravitational wave astronomy was triggered by the first detection of a signal produced by the merger of two compact objects (also known as a compact binary coalescence event). The following detections made by the Earth-based network of advanced interferometers had [...] Read more.
The birth of gravitational wave astronomy was triggered by the first detection of a signal produced by the merger of two compact objects (also known as a compact binary coalescence event). The following detections made by the Earth-based network of advanced interferometers had a significant impact in many fields of science: astrophysics, cosmology, nuclear physics and fundamental physics. However, compact binary coalescence signals are not the only type of gravitational waves potentially detectable by LIGO, Virgo, and KAGRA. An interesting family of still undetected signals, and the ones that are considered in this review, are the so-called continuous waves, paradigmatically exemplified by the gravitational radiation emitted by galactic, fast-spinning isolated neutron stars with a certain degree of asymmetry in their mass distribution. In this work, I will review the status and the latest results from the analyses of advanced detector data. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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16 pages, 4182 KiB  
Review
Squeezing in Gravitational Wave Detectors
by Sheila E. Dwyer, Georgia L. Mansell and Lee McCuller
Galaxies 2022, 10(2), 46; https://doi.org/10.3390/galaxies10020046 - 9 Mar 2022
Cited by 13 | Viewed by 4192
Abstract
Injecting optical squeezed states of light, a technique known as squeezing, is now a tool for gravitational wave detection. Its ability to reduce quantum noise is helping to reveal more gravitational wave transients, expanding the catalog of observations in the last observing run. [...] Read more.
Injecting optical squeezed states of light, a technique known as squeezing, is now a tool for gravitational wave detection. Its ability to reduce quantum noise is helping to reveal more gravitational wave transients, expanding the catalog of observations in the last observing run. This review introduces squeezing and its history in the context of gravitational-wave detectors. It overviews the benefits, limitations and methods of incorporating squeezing into advanced interferometers, emphasizing the most relevant details for astrophysics instrumentation. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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30 pages, 4303 KiB  
Review
Review of the Advanced LIGO Gravitational Wave Observatories Leading to Observing Run Four
by Craig Cahillane and Georgia Mansell
Galaxies 2022, 10(1), 36; https://doi.org/10.3390/galaxies10010036 - 15 Feb 2022
Cited by 35 | Viewed by 5638
Abstract
Gravitational waves from binary black hole and neutron star mergers are being regularly detected. As of 2021, 90 confident gravitational wave detections have been made by the LIGO and Virgo detectors. Work is ongoing to further increase the sensitivity of the detectors for [...] Read more.
Gravitational waves from binary black hole and neutron star mergers are being regularly detected. As of 2021, 90 confident gravitational wave detections have been made by the LIGO and Virgo detectors. Work is ongoing to further increase the sensitivity of the detectors for the fourth observing run, including installing some of the A+ upgrades designed to lower the fundamental noise that limits the sensitivity to gravitational waves. In this review, we will provide an overview of the LIGO detectors optical configuration and lock acquisition procedure, discuss the detectors’ fundamental and technical noise limits, show the current measured sensitivity, and explore the A+ upgrades currently being installed in the detectors. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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64 pages, 3716 KiB  
Review
Stochastic Gravitational-Wave Backgrounds: Current Detection Efforts and Future Prospects
by Arianna I. Renzini, Boris Goncharov, Alexander C. Jenkins and Patrick M. Meyers
Galaxies 2022, 10(1), 34; https://doi.org/10.3390/galaxies10010034 - 14 Feb 2022
Cited by 59 | Viewed by 5067
Abstract
The collection of individually resolvable gravitational wave (GW) events makes up a tiny fraction of all GW signals that reach our detectors, while most lie below the confusion limit and are undetected. Similarly to voices in a crowded room, the collection of unresolved [...] Read more.
The collection of individually resolvable gravitational wave (GW) events makes up a tiny fraction of all GW signals that reach our detectors, while most lie below the confusion limit and are undetected. Similarly to voices in a crowded room, the collection of unresolved signals gives rise to a background that is well-described via stochastic variables and, hence, referred to as the stochastic GW background (SGWB). In this review, we provide an overview of stochastic GW signals and characterise them based on features of interest such as generation processes and observational properties. We then review the current detection strategies for stochastic backgrounds, offering a ready-to-use manual for stochastic GW searches in real data. In the process, we distinguish between interferometric measurements of GWs, either by ground-based or space-based laser interferometers, and timing-residuals analyses with pulsar timing arrays (PTAs). These detection methods have been applied to real data both by large GW collaborations and smaller research groups, and the most recent and instructive results are reported here. We close this review with an outlook on future observations with third generation detectors, space-based interferometers, and potential noninterferometric detection methods proposed in the literature. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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28 pages, 2565 KiB  
Review
Detecting Gravitational Waves with Advanced Virgo
by Ilaria Nardecchia
Galaxies 2022, 10(1), 28; https://doi.org/10.3390/galaxies10010028 - 2 Feb 2022
Cited by 8 | Viewed by 3132
Abstract
Advanced Virgo is the European gravitational-wave detector that, along with the American ones, is part of the global network of detectors that have been pinpointing gravitational waves since 2015. These kilometer-scale laser interferometers, measuring the distance between quasi-free-falling mirrors, represent the suitable detectors [...] Read more.
Advanced Virgo is the European gravitational-wave detector that, along with the American ones, is part of the global network of detectors that have been pinpointing gravitational waves since 2015. These kilometer-scale laser interferometers, measuring the distance between quasi-free-falling mirrors, represent the suitable detectors to explore the Universe through gravitational radiation. The initial Virgo experiment completed several runs of scientific data between 2007 and 2011, establishing the upper limits on the gravitational-wave rate expected for several astrophysical sources. The Advanced Virgo project led this instrument to unprecedented sensitivities making gravitational wave detections a routine occurrence. In this review, the basic techniques to build gravitational-waves interferometers and the upgrades needed to boost their sensitivities, even beyond the classical limit, are presented. The particular case of Advanced Virgo will be described hinting at its future developments, as well. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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31 pages, 4019 KiB  
Review
Detector Characterization and Mitigation of Noise in Ground-Based Gravitational-Wave Interferometers
by Derek Davis and Marissa Walker
Galaxies 2022, 10(1), 12; https://doi.org/10.3390/galaxies10010012 - 14 Jan 2022
Cited by 16 | Viewed by 3340
Abstract
Since the early stages of operation of ground-based gravitational-wave interferometers, careful monitoring of these detectors has been an important component of their successful operation and observations. Characterization of gravitational-wave detectors blends computational and instrumental methods of investigating the detector performance. These efforts focus [...] Read more.
Since the early stages of operation of ground-based gravitational-wave interferometers, careful monitoring of these detectors has been an important component of their successful operation and observations. Characterization of gravitational-wave detectors blends computational and instrumental methods of investigating the detector performance. These efforts focus both on identifying ways to improve detector sensitivity for future observations and understand the non-idealized features in data that has already been recorded. Alongside a focus on the detectors themselves, detector characterization includes careful studies of how astrophysical analyses are affected by different data quality issues. This article presents an overview of the multifaceted aspects of the characterization of interferometric gravitational-wave detectors, including investigations of instrumental performance, characterization of interferometer data quality, and the identification and mitigation of data quality issues that impact analysis of gravitational-wave events. Looking forward, we discuss efforts to adapt current detector characterization methods to meet the changing needs of gravitational-wave astronomy. Full article
(This article belongs to the Special Issue Present and Future of Gravitational Wave Astronomy)
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