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While pulsar timing array (PTA) collaborations have reported evidence for a stochastic gravitational wave background (GWB), the detection of continuous gravitational waves (GWs) from a confirmed supermassive black hole binary (SMBHB) would…

Astrophysics of Galaxies · Physics 2025-10-13 Li-Wen Tian , Yan-Chen Bi , Yu-Mei Wu , Qing-Guo Huang

We investigate the isotropic and anisotropic components of the Stochastic Gravitational Wave Background (SGWB) originated from unresolved merging compact binaries in galaxies. We base our analysis on an empirical approach to galactic…

General Relativity and Quantum Cosmology · Physics 2021-11-16 Giulia Capurri , Andrea Lapi , Carlo Baccigalupi , Lumen Boco , Giulio Scelfo , Tommaso Ronconi

Several pulsar timing array (PTA) experiments such as NANOGrav and PPTA recently reported evidence of a gravitational wave (GW) background at nano-Hz frequency band. This signal can originate from scalar-induced gravitational waves (SIGW)…

Cosmology and Nongalactic Astrophysics · Physics 2025-04-04 Junsong Cang , Yu Gao , Yiming Liu , Sichun Sun

The recent compelling observation of the nanohertz stochastic gravitational wave background has brought to light a new galactic arena to test gravity. In this paper, we derive a formula for the most general expression of the stochastic…

General Relativity and Quantum Cosmology · Physics 2024-04-12 Reginald Christian Bernardo , Guo-Chin Liu , Kin-Wang Ng

The stochastic gravitational wave background (SGWB) can be observed in the nanohertz band using a pulsar timing array (PTA). Here a computationally efficient state-space framework is developed for analysing SGWB data, in which the…

One of the most promising targets for Pulsar Timing Arrays (PTAs) is identifying an individual supermassive black hole binary (SMBHB) out of the population of binaries theorized to produce a gravitational wave background (GWB). In this…

Instrumentation and Methods for Astrophysics · Physics 2026-04-21 Levi Schult , Polina Petrov , Stephen R. Taylor , Nihan Pol , Nima Laal , Maria Charisi , Chung-Pei Ma

The canonical methods for gravitational wave detection are ground- and space-based laser interferometry, pulsar timing, and polarization of the cosmic microwave background. But as has been suggested by numerous investigators, astrometry…

Instrumentation and Methods for Astrophysics · Physics 2018-07-25 Jeremy Darling , Alexandra E. Truebenbach , Jennie Paine

A Gravitational Wave Background (GWB) is expected in the universe from the superposition of a large number of unresolved astrophysical sources and phenomena in the early universe. Each component of the background (e.g., from primordial…

Cosmology and Nongalactic Astrophysics · Physics 2016-04-27 Abhishek Parida , Sanjit Mitra , Sanjay Jhingan

The gravitational-wave background from supermassive binary black holes (SMBBHs) has yet to be detected. This has led to speculations as to whether current pulsar timing array limits are in tension with theoretical predictions. In this…

Astrophysics of Galaxies · Physics 2019-01-07 Xing-Jiang Zhu , Weiguang Cui , Eric Thrane

Pulsar timing array collaborations, such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), are seeking to detect nanohertz gravitational waves emitted by supermassive black hole binaries formed in the aftermath…

Strong evidence for an isotropic, Gaussian gravitational wave background (GWB) has been found by multiple pulsar timing arrays (PTAs). The GWB is expected to be sourced by a finite population of supermassive black hole binaries (SMBHBs)…

General Relativity and Quantum Cosmology · Physics 2026-05-21 William G. Lamb , Jeremy M. Wachter , Andrea Mitridate , Shashwat C. Sardesai , Bence Bécsy , Emily L. Hagen , Stephen R. Taylor , Luke Zoltan Kelley

The recent astronomical milestone by the pulsar timing arrays (PTA) has revealed galactic-size gravitational waves (GW) in the form of a stochastic gravitational wave background (SGWB), correlating the radio pulses emitted by millisecond…

General Relativity and Quantum Cosmology · Physics 2024-11-08 Reginald Christian Bernardo , Kin-Wang Ng

We show that the new precise measurements of Cosmic Microwave Background (CMB) temperature and polarization anisotropies made by the Planck satellite significantly improves previous constraints on the cosmic gravitational waves background…

Cosmology and Nongalactic Astrophysics · Physics 2016-10-17 Luca Pagano , Laura Salvati , Alessandro Melchiorri

Cosmic string networks offer one of the best prospects for detection of cosmological gravitational waves (GWs). The combined incoherent GW emission of a large number of string loops leads to a stochastic GW background (SGWB), which encodes…

A future detection of the Stochastic Gravitational Wave Background (SGWB) with GW experiments is expected to open a new window on early universe cosmology and on the astrophysics of compact objects. In this paper we study SGWB anisotropies,…

Cosmology and Nongalactic Astrophysics · Physics 2020-07-22 N. Bartolo , D. Bertacca , S. Matarrese , M. Peloso , A. Ricciardone , A. Riotto , G. Tasinato

The recent start of the fourth observing run of the LIGO-Virgo-KAGRA (LVK) collaboration has reopened the hunt for gravitational-wave (GW) signals, with one compact-binary-coalescence (CBC) signal expected to be observed every few days.…

General Relativity and Quantum Cosmology · Physics 2024-03-27 Federico De Lillo , Jishnu Suresh

Astrometry, the precise measurement of stellar positions and velocities, offers a promising approach to probing the low-frequency stochastic gravitational wave background (SGWB). Notably, astrometric vector sky maps are sensitive to…

Cosmology and Nongalactic Astrophysics · Physics 2026-04-30 Santiago Jaraba , Sachiko Kuroyanagi , Qiuyue Liang , Meng-Xiang Lin , Mark Trodden

Recent findings from several Pulsar Timing Array (PTA) collaborations point to the existence of a Gravitational Wave Background (GWB) at nanohertz frequencies. A key next step towards characterizing this signal and identifying its origin is…

Cosmology and Nongalactic Astrophysics · Physics 2026-01-16 Thomas Konstandin , Anna-Malin Lemke , Andrea Mitridate , Enrico Perboni

Unresolved sources of gravitational waves can create a stochastic gravitational wave background (SGWB) which may have intrinsic or extrinsic anisotropies. The angular power spectrum is a well-suited estimator for characterizing diffuse…

General Relativity and Quantum Cosmology · Physics 2024-09-27 Deepali Agarwal , Jishnu Suresh , Sanjit Mitra , Anirban Ain

Recent pulsar timing data reported by the NANOGrav collaboration may indicate the existence of a stochastic gravitational wave background around $f \sim 10^{-8}$ Hz. We explore a possibility to generate such low-frequency gravitational…

Cosmology and Nongalactic Astrophysics · Physics 2021-03-24 Yuichiro Nakai , Motoo Suzuki , Fuminobu Takahashi , Masaki Yamada