Welcome!¶
Voids@CPPM is an initiative aiming at exploiting cosmic voids to extract precision cosmological constraints from modern surveys. Cosmic voids are vast, nearly empty regions of the Universe where the matter density is extremely low.
Voids range in size from tens to hundreds of megaparsecs, so large volumes must be observed to detect enough of them to constrain cosmology. Void measurements also benefit particularly from dense galaxy samples. In the past, voids remained largely unexplored in cosmology, but modern large-scale surveys such as Euclid, DESI (Dark Energy Spectroscopic Instrument) and the Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory are now opening a golden age for void science.
The Voids@CPPM team, part of the Cosmology Group at the Centre de Physique des Particules de Marseille (CPPM), has members in Euclid, DESI and Rubin LSST. This puts the group in a unique position to exploit cosmic void measurements, drawing on knowledge of systematics gained across surveys.
Beyond data analysis, the Voids@CPPM team has expertise in analysing simulations and in testing the theoretical models used to extract constraints from cosmic voids. The coming influx of data will let us characterise cosmic voids with unprecedented precision, shedding light on open questions such as the nature of dark energy and the sum of neutrino masses.
Voids@CPPM is funded by the European Research Council (ERC) project COSMOBEST (COSMOlogy BEyond Standard Techniques), led by Alice Pisani, and by a Chaire d'Excellence A*MIDEX from Aix-Marseille Université.
The standard cosmological model relies on dark energy to explain the accelerated expansion of the Universe. Although dark energy makes up about 68% of the Universe, its properties remain largely unknown. Matter is scarce in voids, so dark energy dominates their properties, which makes voids an ideal laboratory for studying it. In particular, the shapes and numbers of cosmic voids carry key information about dark energy. They could reveal whether it played a role earlier in cosmic history, or whether it departs from the predictions of the standard model. Statistics measured from void catalogues, such as the void–galaxy cross-correlation function and the void size function, will greatly improve our understanding of dark energy. Void properties are also sensitive to massive neutrinos and modified gravity, which makes voids a tool of choice in modern cosmology.
Albeit showing promising early constraints, void catalogues built in the last decade contained only a few hundred objects. Thanks to modern survey data such as DESI, Euclid and Rubin LSST, the Voids@CPPM team is building catalogues of hundreds of thousands of voids, delivering unprecedented constraining power and opening a new era for cosmic void cosmology.
