In the vastness of the universe, beyond the twinkling of galaxies, lie enormous regions practically devoid of visible matter, the cosmic voids. These areas, true depressions in the large-scale structure of the cosmos, offer a striking contrast to the dense filaments and galactic clusters that compose the cosmic web. Their characteristics, formation, and role in cosmic evolution intrigue the scientific community, as these voids are not mere absences but natural laboratories where the effects of dark energy and the consequences of cosmic inflation are observed. Exploring these vast spaces thus helps to illuminate the fundamental mysteries of the expansion of the universe and the dynamics of galaxy formation.
By 2025, the advancements observed in the study of cosmic voids rely on the improvement of extensive galaxy surveys and the implementation of increasingly powerful numerical simulations. These tools precisely model the distribution of dark and visible matter, enriching the understanding of the complex interactions between gravity, matter, and energy. In this context, grasping the nature of voids, their diversity, and their evolution seems crucial for deciphering the invisible fabric that underlies the cosmic tapestry.
The vast observation platforms and projects like Euclid or the Legacy Survey of Space and Time are currently contributing to the detailed mapping of voids and the analysis of their physical and dynamic properties. Thanks to this data, scientists question the validity of existing cosmological models, particularly seeking to detect possible deviations from general relativity on large scales, a critical issue for contemporary theoretical physics.
Below, an in-depth look at the multiple facets of cosmic voids, from the first hints of their existence to their current modeling, to better understand their essential role in the complete history of the universe.
In short:
- Cosmic voids are vast regions with very low matter density, characteristic of the large-scale structure of the universe.
- They were discovered during the first systematic surveys of galaxies in the 1970s, ending a decades-long debate.
- These areas are dominated by dark energy, and are studied to understand the acceleration of cosmic expansion.
- Ultra-deep surveys such as those from Euclid allow for a fine characterization of small galaxies within the voids, essential for advanced cosmological tests.
- Recent improvements in void extraction algorithms, using differential topology, allow for precise and robust analysis of structures within the cosmic web.
Origin and discovery of cosmic voids within the cosmic web
The cosmic voids represent the least dense spaces in the observable universe, creating a contrasting frame with the clusters and filaments of galaxies that weave the large-scale structure often compared to a gigantic spider’s web, known as the cosmic web. This cosmic network is primarily made up of dark matter, invisible yet dominating the mass of the universe, around which baryonic matter coalesces to form galaxies and clusters.
The late 1970s marked a revolution in mapping galactic distribution thanks to systematic surveys, notably those from the Sloan Digital Sky Survey. These studies allowed for the formal identification of vast regions almost empty of visible matter. This discovery ended a centuries-old debate initiated as early as 1938, which questioned the homogeneity of galaxy distribution. Increasingly precise data showed that the universe is not isotropic at all scales and that galaxies are organized into complex structures, interwoven with these empty spaces.
These voids typically measure in millions of light-years. In comparison, the Milky Way extends only 100,000 light-years; therefore, the size of voids far exceeds that of galaxies, confirming they form entire regions of the universe. At the heart of these voids, visible matter density drops drastically, forming cavities that influence the overall dynamics of the cosmos.
In this context, the discovery of cosmic filaments, detailed in this resource, sheds light on the role of voids as complementary entities in the hierarchy of cosmic structures. These filaments are the backbones where galaxies concentrate, while the voids are the hollows, giving the universe its characteristic relief architecture.
Physical and dynamic properties of voids: dark matter and dark energy
The cosmic voids are not merely empty spaces devoid of matter, but regions where matter density is significantly lower than elsewhere. A fundamental characteristic is that if ordinary matter and dark matter are removed, the imprint of dark energy remains, a major hypothesis explaining the acceleration of cosmic expansion observed today.
As a result, these zones play a crucial role in studying cosmic evolution by modulating the effect of this mysterious energy. Dark energy is presumed uniform, but its influence can mostly manifest in voids where the gravitational pull exerted by matter is minimal. Observations thus show that the dynamics of small galaxies present in these voids offer a privileged observation ground to test different models of dark energy, including alternatives to the cosmological constant.
To analyze these phenomena, surveys such as Euclid and the Legacy Survey of Space and Time aim to detect galaxies with very low luminosity, making it possible to study the local dynamics effects of voids in detail. These advancements are essential to validate predictions arising from cosmological models and refine the understanding of gravitational interactions in an expanding universe.
Moreover, density profiles obtained from data on millions of galaxies show that density varies significantly from the center to the edges of voids, impacting the formation and distribution of surrounding structures. It is in this perspective that a comparative table of the main physical properties of voids and adjacent dense regions offers a victory of observation and theory.
| Property | Cosmic voids | Dense regions (filaments/clusters) |
|---|---|---|
| Density of matter | ~10% of the average cosmic density | Several times the average density |
| Presence of galaxies | Very low, mainly small galaxies | High number, with massive galaxies |
| Dark energy content | Dominant, influencing local expansion | Inert, with gravity dominant |
| Distribution of dark matter | Low density but structured | Concentrated in galactic halos |
| Typical shape | Generally spherical on average | Filaments and clusters with complex shapes |
Impact of cosmic voids on galaxy formation and evolution
Galaxies evolve differently depending on their environment. Those located in cosmic voids exhibit distinct characteristics in terms of mass, color, star formation rates, and even their chemical content.
According to data from the TNG300 simulation, these galaxies are on average younger, less massive, and have bluer colors, reflecting a higher rate of star formation than those outside the voids. This peculiarity arises from the fact that the low surrounding density less disrupts the internal gravitational sphere and limits the typical interactions and mergers found in dense environments.
Moreover, the lower chemical abundance, particularly of heavy metals, corroborates the hypothesis of slower evolution, with fewer generations of stars. The relationship between galaxies and supermassive black holes also differs according to the medium, with a higher fraction of active black holes in voids, which may indicate specific feeding or regulation mechanisms in these isolated environments.
In this context, the precise analysis of galaxy formation and evolution in cosmic voids is crucial for understanding the fundamental processes of galaxy formation and their current diversity, an indispensable framework for modern and complete cosmology.
The above video illustrates advanced simulations modeling the dynamics of voids and the formation of galaxies in these environments, clearly exposing the structural differences with galaxies located in cosmic filaments.
Techniques for identifying and analyzing cosmic voids in astronomical surveys
The detection and systematic study of cosmic voids have long been hindered by their imposing size and the complexity of their morphology. The diversity of individual void shapes, often very far from ideal sphericity, complicates their identification.
The great technological breakthrough came with the development in 2007 of two key algorithms, DISPERSE and ZOBOV, released as open source, which rely on concepts of differential topology to robustly detect voids despite distortions in the galactic distribution. These methods have led to the creation of open catalogs based on data from the Sloan Digital Sky Survey, and then from surveys like the Dark Energy Survey, thus multiplying applications and studies.
Recently launched, the VIDE analysis chain synthesizes these advancements to construct powerful and accessible void databases, facilitating large-scale statistical analyses. These computational tools enrich observational cosmology by allowing precise testing of the universe’s expansion according to the cosmological principle, thus validating the equality between the average angular and radial sizes of voids over large distances.
Cosmic voids and their evolution
Discover how the vast, almost empty regions of the Universe evolve through cosmic time.
Graph illustrating the evolution of the average size of cosmic voids according to cosmic time expressed in billions of years.
This video details the algorithmic methods for identifying and characterizing voids, as well as their role in understanding the cosmic web and the expansion of the universe.
Recent perspectives and future challenges in the study of cosmic voids
The latest research demonstrates that cosmic voids provide precise constraints on cosmological parameters, notably the material content of the universe, while not currently indicating any significant deviation from general relativity or the measurements of the Planck mission.
The advancements enabled by processing data from increasingly vast and deep surveys, coupled with the evolution of computers and algorithms, are producing increasingly fine three-dimensional maps that reveal the complexity of the cosmic network. Thus, emphasis is placed on the upcoming exploitation of data from the Euclid mission, which should provide unprecedented constraints on the nature of dark energy.
By combining observations and numerical simulations, researchers anticipate a renewed understanding of the influence of voids on cosmic dynamics at large scales and on the formation of galaxies in extreme environments. This approach paves the way for new theories regarding fundamental physics, including modified gravity and other exotic models beyond the current paradigm.
The deeply interactive nature of the cosmos is thus gradually illuminated, and the cosmic voids reveal themselves to be major players in the grand narrative of the Universe.
What is a cosmic void?
A cosmic void is a vast region of the universe where the density of matter, visible or dark, is extremely low compared to the densely populated regions of galaxies.
How do cosmic voids influence the expansion of the universe?
The voids, dominated by dark energy, allow observing the effects of this mysterious energy on the local dynamics, helping to measure and test the evolution of cosmic expansion.
What methods are used to detect cosmic voids?
Algorithms based on differential topology, such as DISPERSE and ZOBOV, identify voids from galactic surveys, even in the presence of complex deformations in the spatial distribution of galaxies.
Why do galaxies in cosmic voids differ from those in dense regions?
Galaxies in voids are generally smaller, younger, with higher star formation rates and less rich chemical compositions in metals, due to their low-density and isolated environment.
What is the future of the study of cosmic voids?
With the advances in observational data and simulations, the study of cosmic voids will continue to provide valuable information for understanding the nature of dark energy and testing gravity on large scales.