Pulsar Timing Array in the past decade

TL;DR

Over the past decade, pulsar timing arrays have significantly advanced in instrumentation, data analysis, and theoretical understanding, culminating in evidence for a gravitational-wave background and nearing confident detection of nanohertz GWs.

Contribution

This paper provides a comprehensive overview of the rapid progress in PTA experiments and their role in detecting nanohertz gravitational waves over the last decade.

Findings

Detection of a common red-noise process in pulsar data

Evidence for the Hellings-Downs correlation in 2023

Steady improvement in PTA sensitivity and upper limits

Abstract

The past decade has been a transformative period for pulsar timing arrays (PTAs) and their search for nanohertz gravitational waves (GWs). This progress has been driven by collective advances in instrumentation for pulsar timing observations, increasingly sophisticated data-analysis techniques, and improved theoretical understanding of the origins of nanohertz GW signals. PTA sensitivity has steadily improved, leading first to progressively more stringent upper limits on the gravitational-wave background (GWB), and subsequently to the identification of a common red-noise process in pulsar timing data, the first hint of a GWB. In 2023, multiple PTA collaborations reported evidence for the Hellings-Downs correlation, widely regarded as the definitive signature of a GWB. These developments place PTAs on the threshold of a confident GW detection and the opening of a new low-frequency window on the GW Universe. In this article, we present an overview of PTA experiments, with particular emphasis on the rapid progress achieved during this pivotal period for PTA and nanohertz GW science.