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After Pulsar Timing Arrays (PTAs) have announced the evidence for a low-frequency gravitational wave background (GWB), the continuous waves (CWs) are the next anticipated gravitational wave (GW) signals. In this work, we model CW sources…

Gravitational wave (GW) backgrounds of cosmological origin are expected to be nearly isotropic, with small anisotropies resembling those of the cosmic microwave background. We analyse the case of a scalar-induced GW background and clarify…

Cosmology and Nongalactic Astrophysics · Physics 2023-01-18 Ema Dimastrogiovanni , Matteo Fasiello , Ameek Malhotra , Gianmassimo Tasinato

Pulsar Timing Arrays (PTAs) have recently found strong evidence for low-frequency gravitational waves (GWs) in the nanohertz frequency regime. As GWs pass, they produce deviations in measured lengths and light-travel times. PTA experiments…

High Energy Astrophysical Phenomena · Physics 2025-05-05 Luke Zoltan Kelley

The paucity of observed supermassive black hole binaries (SMBHBs) may imply that the gravitational wave background (GWB) from this population is anisotropic, rendering existing analyses sub-optimal. We present the first constraints on the…

We investigate the effects of gravitational waves (GWs) from a simulated population of binary super-massive black holes (SMBHs) on pulsar timing array datasets. We construct a distribution describing the binary SMBH population from an…

Cosmology and Nongalactic Astrophysics · Physics 2015-06-11 V. Ravi , J. S. B. Wyithe , G. Hobbs , R. M. Shannon , R. N. Manchester , D. R. B. Yardley , M. J. Keith

The nano-hertz (nHz) stochastic gravitational wave background (SGWB), generated by unresolved supermassive black hole binaries (SMBHBs), provides a unique probe of their population and its cosmic evolution. In this work, we explore the…

Cosmology and Nongalactic Astrophysics · Physics 2025-10-28 Mohit Raj Sah , Suvodip Mukherjee

Following the recent evidence for a gravitational wave (GW) background found by pulsar timing array (PTA) experiments, the next major science milestone is resolving individual supermassive black hole binaries (SMBHBs). The detection of…

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

We present a refined estimation of the stochastic gravitational wave background (SGWB) based on observed dual active galactic nuclei (AGNs) together with AGN X-ray luminosity functions, in light of recent Pulsar Timing Array detections of…

High Energy Astrophysical Phenomena · Physics 2026-01-14 Katsunori Kusakabe , Yoshiyuki Inoue , Daisuke Toyouchi

The nano-Hertz gravitational wave background (GWB) is a key probe of supermassive black hole (SMBH) formation and evolution, if the background arises predominantly from binary SMBHs. The amplitude of the GWB, which is typically quantified…

Astrophysics of Galaxies · Physics 2023-06-02 Jean J. Somalwar , Vikram Ravi

In recent years, several pulsar timing array collaborations have reported evidence for a nanohertz gravitational wave background (GWB). Such a background signal could be produced by supermassive binary black holes, early-Universe processes…

Anisotropies in the nanohertz gravitational-wave background are a compelling next target for pulsar timing arrays (PTAs). Measurements or informative upper limits to the anisotropies are expected in the near future and can offer important…

Cosmology and Nongalactic Astrophysics · Physics 2025-08-26 Gabriela Sato-Polito , Marc Kamionkowski

The advent of gravitational-wave (GW) astronomy has presented us with a completely new means for observing the Universe, allowing us to probe its structure and evolution like never before. In this thesis, we explore three distinct but…

General Relativity and Quantum Cosmology · Physics 2022-03-14 Alexander C. Jenkins

We present the results of simulated injections testing the first Bayesian search-pipeline capable of investigating the angular-structure of a gravitational-wave (GW) background influencing pulsar signals. A stochastic background of GWs from…

General Relativity and Quantum Cosmology · Physics 2013-10-30 Stephen R. Taylor , Jonathan R. Gair

We compute the isotropic gravitational wave (GW) background produced by binary supermassive black holes (SBHs) in galactic nuclei. In our model, massive binaries evolve at early times via gravitational-slingshot interaction with nearby…

Astrophysics of Galaxies · Physics 2017-05-04 Alexander Rasskazov , David Merritt

Pulsar Timing Arrays (PTA) around the world are using the incredible consistency of millisecond pulsars to measure low frequency gravitational waves from (super)Massive Black Hole (MBH) binaries. We use comprehensive MBH merger models based…

High Energy Astrophysical Phenomena · Physics 2017-09-06 Luke Zoltan Kelley , Laura Blecha , Lars Hernquist , Alberto Sesana , Stephen R. Taylor

We estimate the amplitude of the nano-Hz stochastic gravitational wave background (GWB) resulting from an unresolved population of inspiralling massive black hole binaries (MBHBs). To this aim, we use the L-Galaxies semi-analytical model…

Astrophysics of Galaxies · Physics 2021-11-24 David Izquierdo-Villalba , Alberto Sesana , Silvia Bonoli , Monica Colpi

Significant evidence for a stochastic gravitational-wave background has recently been reported by several Pulsar Timing Array observations. These studies have shown that, in addition to astrophysical explanations based on supermassive black…

Cosmology and Nongalactic Astrophysics · Physics 2024-02-13 Ran Ding , Chi Tian

The astrophysical Stochastic Gravitational Wave Background (SGWB) originates from the mergers of compact binary objects that are otherwise undetected as individual events, along with other sources such as supernovae, magnetars, etc. The…

General Relativity and Quantum Cosmology · Physics 2023-11-01 Mohit Raj Sah , Suvodip Mukherjee

Context. The Astrophysical Gravitational Wave Background (AGWB) is a collective signal of astrophysical gravitational wave sources and is dominated by compact binaries. Its measurement is one of the science goals of current and future…

High Energy Astrophysical Phenomena · Physics 2024-02-14 Seppe Staelens , Gijs Nelemans