A Gamma-ray Infrastructure to Advance Gravitational Wave Astrophysics

Project Information

GIGA

Grant agreement ID: 101116134

DOI

10.3030/101116134

EC signature date 5 December 2023

Start date 1 January 2024

End date 31 December 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 658 500,00

EU contribution

€ 1 658 500,00

Coordinated by

STICHTING NEDERLANDSE WETENSCHAPPELIJK ONDERZOEK INSTITUTEN
Netherlands

Periodic Reporting for period 1 - GIGA (A Gamma-ray Infrastructure to Advance Gravitational Wave Astrophysics)

Reporting period: 2024-01-01 to 2026-06-30

Summary of the context and overall objectives of the project

Most large galaxies contain a supermassive black hole at their centre. When galaxies collide and merge, these black holes are expected to form pairs and spiral together, releasing energy as gravitational waves. A large population of such pairs across the Universe would produce a faint background signal known as the gravitational wave background (GWB). Detecting this signal would reveal how galaxies and black holes formed and evolved, and could expose new physics not yet explained by current theories. Pulsar timing arrays (PTAs) are currently the only tool capable of detecting the GWB. They use an array of extremely stable rotating neutron stars as a cosmic detector, tracking tiny changes in the arrival times of their pulses over many years. Radio telescope PTAs have recently found strong evidence for the GWB. However, radio waves are distorted by the gas between stars, which limits sensitivity and can bias results. GIGA builds a pulsar timing array using gamma rays recorded by NASA's Fermi space telescope. Gamma rays are not affected by interstellar gas, providing a clean and independent measurement of the GWB. GIGA's four objectives are to: detect the GWB independently; characterise its astrophysical origins; study the properties of the interstellar gas; and search for signatures of dark matter and new physics.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The first reporting period (January 2024 to December 2025) saw strong progress across all work areas. A dedicated computing cluster became fully operational in early 2025, providing the power needed for large data analyses and shared with the broader astronomical community. Three million CPU hours were also secured through national computing grants. The full archive of Fermi gamma ray pulsar data has been transferred and is being prepared for the first GIGA data release. Several key scientific results were produced. A major analysis interpreting the GWB signal detected by the European Pulsar Timing Array was published in 2024. A study comparing GWB evidence across all major radio pulsar timing arrays was also published. Three papers reporting 4.2 sigma evidence for the GWB from the MeerKAT radio telescope have been also been published. A new analysis framework for the GIGA gamma ray data has been accepted for publication and forms the technical foundation for the upcoming GIGA data release. Two interstellar medium research programmes are underway. The first has produced a simulation tool, that creates realistic models of the gas between stars and shows how that gas biases gravitational wave searches. The second is a large study of how gas properties change over time across many pulsars. The European Pulsar Timing Array collaboration received two international awards in 2025, from the Royal Astronomical Society and the Chinese Academy of Sciences, for its GWB detection work. The GIGA team played a leading role in that research. A team of doctoral and postdoctoral researchers is actively producing results and presenting at international conferences. A scientific workshop jointly funded by WE Heraeus and the Lorentz Center will be held in May 2026 in the Netherlands.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The interstellar medium simulation tool developed within GIGA is the first of its kind. It produces realistic, layered models of the gas between stars and reveals how that gas biases gravitational wave detection. It will be released as open source software for use by the global pulsar timing community.
More broadly, using gamma rays as a gravitational wave detector is a new approach to one of the most ambitious experiments in modern science. As GIGA grows in sensitivity, it will provide the first independent confirmation of the gravitational wave background, free from the noise that affects radio measurements. This will be a landmark result with deep implications for our understanding of how galaxies, black holes, and the Universe itself have evolved.