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In the next decade gravitational waves might be detected using a pulsar timing array. In an effort to develop optimal detection strategies for stochastic backgrounds of gravitational waves in generic metric theories of gravity, we…

High Energy Astrophysical Phenomena · Physics 2013-05-30 Sydney J. Chamberlin , Xavier Siemens

Supermassive black hole binaries are the strongest gravitational wave sources in the universe. The systems most likely to be observed with pulsar timing arrays (PTAs) will have particularly high masses ($\gtrsim 10^9 M_\odot$), long periods…

High Energy Astrophysical Phenomena · Physics 2014-11-17 Jeremy D. Schnittman

The positive evidence of a nano-hertz gravitational wave background recently found by several pulsar timing array (PTA) collaborations opened up a window to test modified gravity theories in a unique frequency band in parallel to other…

Cosmology and Nongalactic Astrophysics · Physics 2024-05-21 Qiuyue Liang , Ippei Obata , Misao Sasaki

Gravitational waves (GWs) at ultra-low frequencies (${\lesssim 100\,\mathrm{nHz}}$) are key to understanding the assembly and evolution of astrophysical black hole (BH) binaries with masses $\sim 10^{6}-10^{9}\,M_\odot$ at low redshifts.…

Cosmology and Nongalactic Astrophysics · Physics 2021-10-26 Christopher J. Moore , Alberto Vecchio

In the summer of 2023, the pulsar timing arrays (PTAs) announced a compelling evidence for the existence of a nanohertz stochastic gravitational wave background (SGWB). Despite this breakthrough, however, several critical questions remain…

Cosmology and Nongalactic Astrophysics · Physics 2025-04-16 Reginald Christian Bernardo , Kin-Wang Ng

Pulsar Timing Array (PTA) observations hinted towards the existence of a stochastic gravitational wave background (SGWB) in the nHz frequency band. Still, the nature of the SGWB signal cannot be confidently inferred from current data, and…

Cosmology and Nongalactic Astrophysics · Physics 2024-04-04 Stanislav Babak , Mikel Falxa , Gabriele Franciolini , Mauro Pieroni

Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial correlation. Here we…

With the strong evidence for a gravitational wave (GW) background in the nanohertz frequency band from pulsar timing arrays, the detection of continuous GWs from individual supermassive black hole binaries is already at the dawn. Utilizing…

General Relativity and Quantum Cosmology · Physics 2024-10-23 Dicong Liang , Siyuan Chen , Chao Zhang , Lijing Shao

Multiple pulsar timing array (PTA) collaborations have recently reported the first detection of gravitational waves (GWs) of nanohertz frequencies. The signal is expected to be primarily sourced by inspiralling supermassive black hole…

Cosmology and Nongalactic Astrophysics · Physics 2023-12-13 Gabriela Sato-Polito , Matias Zaldarriaga , Eliot Quataert

The recently released data by pulsar timing array (PTA) collaborations have amassed substantial evidence corroborating the existence of a stochastic signal consistent with a gravitational-wave background at frequencies around the nanohertz…

Cosmology and Nongalactic Astrophysics · Physics 2025-03-27 Lang Liu , Zu-Cheng Chen , Qing-Guo Huang

Massive black-hole binaries, formed when galaxies merge, are among the primary sources of gravitational waves targeted by ongoing Pulsar Timing Array (PTA) experiments and the upcoming space-based LISA interferometer. However, their…

Astrophysics of Galaxies · Physics 2017-07-26 Irina Dvorkin , Enrico Barausse

Black-holes are known to span at least 9 orders of magnitude in mass: from the stellar-mass objects observed by the Laser Interferometer Gravitational-Wave Observatory Scientific Collaboration and Virgo Collaboration, to supermassive…

General Relativity and Quantum Cosmology · Physics 2021-02-03 Andrew R. Kaiser , Sean T. McWilliams

The search for gravitational waves using Pulsar Timing Arrays (PTAs) is a computationally expensive complex analysis that involves source-specific noise studies. As more pulsars are added to the arrays, this stage of PTA analysis will…

High Energy Astrophysical Phenomena · Physics 2022-11-28 Lorenzo Speri , Nataliya K. Porayko , Mikel Falxa , Siyuan Chen , Jonathan R. Gair , Alberto Sesana , Stephen R. Taylor

Super-massive black hole binaries are expected to produce a GW signal in the nano-Hertz frequency band which may be detected by PTAs in the coming years. The signal is composed of both stochastic and individually resolvable components. Here…

Instrumentation and Methods for Astrophysics · Physics 2019-07-17 Janna Goldstein , John Veitch , Alberto Sesana , Alberto Vecchio

Pulsar timing uses the highly stable pulsar spin period to investigate many astrophysical topics. In particular, pulsar timing arrays make use of a set of extremely well-timed pulsars and their time correlations as a challenging detector of…

Astrophysics of Galaxies · Physics 2021-12-16 Michele Maiorano , Francesco De Paolis , Achille A. Nucita

In the nanohertz band, the spatial correlations in pulsar timing arrays (PTAs) produced by interfering gravitational waves (GWs) from multiple sources likely deviate from the traditional ones without interference under the assumption of an…

General Relativity and Quantum Cosmology · Physics 2025-10-01 Yu-Mei Wu , Yan-Chen Bi , Qing-Guo Huang

By inferring the gravitational wave background (GWB) from a population of supermassive black hole binaries (SMBHBs), pulsar timing arrays (PTAs) enable the study of massive black holes. In many ways, PTAs manifest the promise of a…

High Energy Astrophysical Phenomena · Physics 2025-12-16 Nima Laal , Stephen R. Taylor , Cayenne Matt , Kayhan Gultekin

Recently, several major pulsar timing array (PTA) collaborations have assembled strong evidence for the existence of a gravitational-wave background at frequencies around the nanohertz regime. Assuming that the PTA signal is attributed to…

Cosmology and Nongalactic Astrophysics · Physics 2025-03-27 Lang Liu , You Wu , Zu-Cheng Chen

We explore the potential of Pulsar Timing Arrays (PTAs) such as NANOGrav, EPTA, and PPTA to detect the Stochastic Gravitational Wave Background (SGWB) in theories of massive gravity. In General Relativity, the function describing the…

Cosmology and Nongalactic Astrophysics · Physics 2021-10-27 Qiuyue Liang , Mark Trodden

Using public pulse time-of-arrival data from five pulsar timing arrays (PTAs), we search for a stationary, isotropic, and unpolarized nHz stochastic gravitational-wave background (SGWB). This analysis is more sensitive than previous…

Cosmology and Nongalactic Astrophysics · Physics 2026-04-29 Wang-Wei Yu , Bruce Allen