Timing the cosmic expansion with gravitational-waves dark sirens: from compact binaries to large scale structures

For 20-years, measurements of the Universe expansion rate from close-by and far sources are in tension hinting at the presence of new physics.

Our struggle to study the Universe's expansion is due to the difficulty of observing cosmological sources for which the distance is known.

Gravitational Waves (GWs) from compact binary coalescences (CBCs) are emergent cosmological probes that provide directly the distance of the source thus taking the name of Standard Sirens.

Unfortunately, they do not provide the other ingredient to measure the Universe expansion: the redshift.GravitySirens is an ambitious project aiming to measure the cosmic expansion with CBCs and exploit their link with the astrophysical environment to obtain implicit redshift information.

GravitySirens will focus on the population and astrophysical properties of GW sources that can allow a more precise measure of the cosmic expansion.

My team and I will exploit data delivered in the next 5-years from the GW detectors LIGO, Virgo, KAGRA, the satellite Euclid, and Arrays of Radio telescopes such as HERA, MeerKAT and SKAO.

By using a mixture of population synthesis codes and semi-analytical models, we will jointly infer how fast the universe is expanding and how CBCs relate to galaxies and large-scale structures (LSS).

We will use state-of-the-art technologies such as machine learning and graphical process units to construct efficient algorithms for population analyses and use scientific data delivered in the upcoming years.

GravitySirens will provide the most accurate and precise GW-based measures of the Universe expansion and measure the link between CBCs, galaxies and LSSs.

On one hand, the cosmic expansion measures that GravitySirens will provide can potentially lead us to the discovery of new physics at cosmological scales.

On the other hand, inferring the relationship between CBCs, galaxies and LSS tracers will point us to the processes acting for compact object formation.