Observable universe#Large-scale structure

The structure of the cosmos is characterized by the large-scale arrangement and distribution of observable matter in the universe. Astronomy and Cosmology observe the universe in order to understand its structures on a large scale.

• 2.1 Procedures
• 2.2 Problems

Large-scale structure

Currently, many structures are already known: star are summarized in galaxies, galaxies in clusters of galaxies, in turn, and then in superclusters, between which large voids ( voids) are located. Until 1989, it was assumed superclusters are distributed relatively evenly over the entire space and formed the largest structures in the universe. Discovered in 1989 Margaret Geller and John Huchra then using data from the study of the redshift, the Great Wall, an elongated cluster of galaxies. It has a length of 500 million light years and a width of 200 million light- years, but has only a depth of 15 million light years. The Great Wall remained so long unnoticed, because the detection of the positions of the galaxies was necessary in three dimensions for their discovery. This was achieved by combining the two-dimensional spatial data of the galaxies with the distance data from the redshift.

In the direction of the constellations Hydra and Centaur, about 250 million light years away from the Virgo Supercluster, in which the Milky Way is, there is a gravimetric anomaly called great attractors. This anomaly pulls galaxies up to a distance of several hundred million light years. The light of all these galaxies is indeed shifted by the Hubble law, but the subtle differences in the redshift make it possible to prove the great attractor, or at least the existence of a mass accumulation in the order of several tens of thousands of galaxies. In the center of the great attractor is the hidden almost through the Milky Way disk Norma cluster of galaxies. In its vicinity there is a collection of many large and old galaxies, many of which collide with each other and / or release large amounts of radiation.

Orders of magnitude

On the currently largest observable scale one finds clusters of galaxies that come together to even larger superclusters. These in turn form thread-like filaments, the huge, bubble-like, practically galaxies free cavities (English voids, gaps ', ' white space ') span. One speaks sometimes of the honeycomb-like structure (so called cosmic web) of the universe.

This results in the following ranking of the largest to the smallest structures of the observable universe:

Note: Some of the listed size scales overlap each other. Example, there are moons, exceed the planet 's size, asteroids, which are substantially larger than some moons, etc. In fact, the classification of celestial objects is due to their size in astronomy currently very controversial, such as the question of which solar satellites to the planets should be counted and which are not (Pluto, Plutinos, Trans Neptune, etc.).

Research

In cosmology is an attempt to create a model of the large space structure of our universe. Above all, the Big Bang model and assumptions about the nature of matter in the universe are considered. Thus, it is possible to make predictions about the distribution of matter in space, which are compared with the observations and thus make it possible to improve the theories. This happens, among other things in the context of cosmological simulations. At present, the observations suggest that most of the universe consists of cold dark matter. Theories that work, however, with hot or baryonic dark matter, do not provide good predictions. Other ways to look at these models are possible on the basis of minimal fluctuations in the cosmological background radiation or with strongly redshifted supernovae. It is a growing consensus that all these approaches provide a result: We live in an accelerated universe.

Method

Another way to bring about the large-scale structure of the cosmos in experience, is the so-called Lyman -alpha forest. This is a collection of spectral lines in the light from quasars. They are considered relatively safe indication of the existence of giant interstellar gas clouds (which are mainly composed of hydrogen). These gas clouds in turn appear to influence the formation of new galaxies.

In the exploration of large-scale structures, the effect of gravitational lensing is observed. This curve the course of light rays so that the image of an object may be in a direction other than the object itself. This is (eg galaxies) caused by objects in the foreground that curve ( according to the general theory of relativity ) the space around them and so divert the light beams. Strong gravitational lenses are even useful, because they can magnify distant galaxies, which are thus easier to spot. The weak gravimetric shear by lying between the source and observer universe, the observed structure here but crucial change and thus complicate the observation. This shearing in turn can serve for verification of different cosmological models.

Problems

The large-scale structure of the universe is, however, not reproduced realistically by the sole use of the redshift for distance determination. For example, galaxies would be attracted behind a cluster of this and so slightly blue-shifted to be ( compared to the situation without the cluster). Before, however, the cluster galaxies were slightly red-shifted. The environment of the cluster would therefore appear somewhat flattened. An opposite effect can be observed in the galaxies in a cluster: These possess any random movements around the center of the cluster, which - when transformed into a red shift - give a stretched image. This causes a phenomenon known as the " finger of God ": the illusion of a large number of galaxies, pointing to the earth.