Vide (astronomie)

Résumé

En astronomie, un vide est un espace dont la densité de matière est extrêmement faible situé entre des filaments galactiques reliant des superamas, les plus grandes structures de l'univers. Ces vides ont généralement un diamètre allant de 11 à 150 Mpc. Lorsque des vides prennent de telles dimensions, ils sont parfois appelés supervides. Les vides situés dans des régions à forte densité de matière sont plus petits que ceux situés dans des régions moins denses de l'univers. Liste des vides Un recensement de 1994 a établi une liste de 27 supervides situés à une distance inférieure à 740 Mpc. Le tableau ci-dessous ne mentionne pas :

le Vide local,
le vide du Capricorne,
le vide de Cassiopée-Céphée,
le vide de la Chevelure (de Bérénice),
le vide de la Colombe,
le vide du Fourneau,
le vide du Grand Chien,
le vide de l'Éridan,
le vide d'Hercules,
le ,
le vide d'Ophiuchus,
le vide de Pégase,
le vide de Persée-Poissons,
le vide du Sculpteur,
le (d

Source officielle

https://fr.wikipedia.org/wiki/Vide_(astronomie)

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Cours associés (3)

Cosmology is the study of the structure and evolution of the universe as a whole. This course describes the principal themes of cosmology, as seen from the point of view of observations.

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The principles of 3D surface (SEM) reconstruction and its limitations will be explained. 3D volume reconstruction and tomography methods by electron microscopy (SEM/FIB and TEM) will be explained and compared with x-ray tomography.

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Irradiated austenitic stainless steels, because of their low stacking fault energy and high shear modulus, should exhibit a high ratio of stacking fault tetrahedra relative to the overall population of radiation induced nanometric defects. Experimental observations of stacking fault tetrahedra by transmission electron microscopy in commercial-purity stainless steels are however scarce, while they abundantly occur in high-purity or model austenitic alloys irradiated at both low and high temperatures, but not at around 673 K. In commercial alloys, the little evidence of stacking fault tetrahedra does not follow such a trend. These contradictions are reviewed and discussed. Reviewing the three possible formation mechanisms identified in the literature, namely the Silcox and Hirsch Frank loop dissociation, the void collapse and the stacking fault tetrahedra growth, it seems that the later dominates under irradiation. (C) 2013 Elsevier B. V. All rights reserved.

Elsevier Science Bv2013

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Cosmic void baryon acoustic oscillation measurement: evaluation of sensitivity to selection effects

Daniel Felipe Forero Sanchez, Jean-Paul Richard Kneib, Amélie Tamone, Andrei Variu, Cheng Zhao

Cosmic voids defined as a subset of Delaunay triangulation (DT) circumspheres have been used to measure the baryon acoustic oscillations (BAO) scale; providing tighter constraints on cosmological parameters when combined with matter tracers. These voids are defined as spheres larger than a given radius threshold, which is constant over the survey volume. However, the response of these void tracers to observational systematics has not yet been studied. In this work, we analyse the response of void clustering to selection effects. We find for the case of moderate (

OXFORD UNIV PRESS2022

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Morphological Segregation in the Surroundings of Cosmic Voids

Elena Ricciardelli, Amélie Tamone

We explore the morphology of galaxies living in the proximity of cosmic voids, using a sample of voids identified in the Sloan Digital Sky Survey Data Release 7. At all stellar masses, void galaxies exhibit morphologies of a later type than galaxies in a control sample, which represent galaxies in an average density environment. We interpret this trend as a pure environmental effect, independent of the mass bias, due to a slower galaxy build-up in the rarefied regions of voids. We confirm previous findings about a clear segregation in galaxy morphology, with galaxies of a later type being found at smaller void-centric distances with respect to the early-type galaxies. We also show, for the first time, that the radius of the void has an impact on the evolutionary history of the galaxies that live within it or in its surroundings. In fact, an enhanced fraction of late-type galaxies is found in the proximity of voids larger than the median void radius. Likewise, an excess of early-type galaxies is observed within or around voids of a smaller size. A significant difference in galaxy properties in voids of different sizes is observed up to 2 R-void, which we define as the region of influence of voids. The significance of this difference is greater than 3 sigma for all the volume-complete samples considered here. The fraction of star-forming galaxies shows the same behavior as the late-type galaxies, but no significant difference in stellar mass is observed in the proximity of voids of different sizes.

Iop Publishing Ltd2017

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