Cosmic voids in the universe
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Cosmic Voids: Definition and Importance in Cosmology
Cosmic voids are vast, underdense regions in the universe, making up a significant part of the cosmic web. These regions are where the effects of cosmic expansion and acceleration are most pronounced, and they play a crucial role in understanding the large-scale structure and evolution of the universe 123. Unlike dense clusters of galaxies, voids are less affected by complex baryonic physics, making them clean environments to study fundamental cosmological parameters and the laws of gravity 26.
Structure, Properties, and Dynamics of Cosmic Voids
Density and Velocity Profiles
Cosmic voids have characteristic density profiles, with a low central density that gradually increases toward the edges. These profiles are found to be universal across different void sizes and redshifts, described accurately by simple empirical functions with only a few parameters . The velocity profiles of voids, which describe how matter flows around and out of voids, also follow predictable patterns and agree well with theoretical models . The bulk motion of voids is significant, with mean velocities around 400 km/s, and is influenced by the surrounding large-scale environment. Smaller voids and those in denser regions tend to move faster .
Evolution and Linearity
The dynamics of cosmic voids remain close to linear, especially for larger voids, which allows them to connect late-time large-scale structure to early universe physics. However, smaller voids can introduce non-linearities, so focusing on larger voids helps maintain this linear relationship .
Observational Signatures and Cosmological Applications
Probing Dark Energy, Gravity, and Neutrinos
Voids are highly sensitive to diffuse components like dark energy and neutrinos, making them powerful probes for testing new physics and modifications to gravity 123. Observables such as the void distribution function, redshift-space distortions, and gravitational lensing around voids provide valuable information for constraining cosmological parameters, including the Hubble parameter and the matter and dark energy densities 124.
Weak Lensing and Doppler Lensing
Weak gravitational lensing and Doppler lensing around voids offer complementary ways to infer their mass profiles and improve constraints on cosmological models. Combining these techniques leads to tighter constraints and better agreement between different methods of measuring void properties .
Robustness Against Baryonic Effects
Studies show that cosmic voids are minimally affected by baryonic physics, especially when identified using dark matter or halo tracers. This robustness enhances their reliability as cosmological probes, as their properties remain consistent across different simulation methods .
Advances in Void Science: Machine Learning and Surveys
Machine learning techniques are now being used to extract cosmological information from void properties such as ellipticity, density contrast, and radius. These methods can constrain key cosmological parameters with high accuracy, even without using spatial information from void catalogs . Upcoming large-area spectroscopic surveys with imaging capabilities are expected to provide detailed maps of voids, further unlocking their potential for cosmological studies 23.
Conclusion
Cosmic voids are essential features of the universe that offer unique insights into its composition, expansion, and the laws governing it. Their universal properties, sensitivity to fundamental physics, and robustness against complex baryonic effects make them powerful tools for cosmology. As observational techniques and data analysis methods advance, the study of cosmic voids is poised to answer some of the most pressing questions about the universe’s origin, structure, and fate 12346810.
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