Structure of the cosmos

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Structure of the universe
This deep-field image from the Hubble telescope shows around 1500 different galaxies in a section of the sky that is only 144 arcseconds in size and thus illustrates the size and breadth of the universe.

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

Spacious structure

At present, have been known many structures: Stars are summarized in galaxies, galaxies turn into clusters of galaxies and these then in superclusters between which large voids (, voids ) are located. Until 1989, it was assumed that superclusters were relatively evenly distributed over entire space and formed the largest structures in our universe. Then in 1989 Margaret Geller and John Huchra discovered the Great Wall , an elongated collection of galaxies, using data from their redshift study . It is 500 million light years long and 200 million light years wide, but is only 15 million light years deep. The Great Wall went unnoticed for so long because it was necessary to record the positions of the galaxies in three dimensions in order to be discovered. This was achieved by combining the two-dimensional location 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 from the Virgo supercluster , which also contains the Milky Way , there is a gravimetric anomaly called the Great Attractor . This anomaly attracts galaxies up to several hundred million light years away. The light of all these galaxies is shifted according to Hubble's law , but the subtle differences in redshift make it possible to detect the Great Attractor or at least the existence of a mass accumulation on the order of tens of thousands of galaxies. In the center of the large attractor lies the Norma galaxy cluster, which is almost hidden by the Milky Way disk . In its vicinity is a collection of many large and ancient galaxies, many of which collide with one another and / or emit large amounts of radiation.

Orders of magnitude

On what is currently the largest observable scale, one finds galaxy clusters that come together to form even larger superclusters . These in turn form thread-like filaments that span huge, bubble-like, practically galaxy-free cavities ( Voids , gaps, “empty spaces”). Sometimes one speaks of the honeycomb structure of the universe ( cosmic web ).

The following ranking results from the largest to the smallest structures of the observable universe:

  1. Large Quasar Group (LQG) (e.g .: U1.27 , diameter: about 4 billion light years)
  2. Filaments and Voids (e.g. Great Wall , diameter: about 1 billion light years )
  3. Superclusters (e.g. Virgo superclusters , diameter: about 200 million light years)
  4. Galaxy clusters (e.g. local group , diameter: about 10 million light years)
  5. Galaxies (e.g. Milky Way , diameter: about 100,000 light years)
  6. Star clusters ( globular clusters , open star clusters , diameter: dozens to hundreds of ly.)
  7. Planetary systems (e.g. our solar system, diameter: about 300  AU = 41 light hours)
  8. Stars (e.g. sun, diameter: 1,392,500 km = 4.65 light seconds)
  9. Planets (e.g. Earth, diameter: 12,756.2 km = 42.6 light milliseconds)
  10. Moons (e.g. earth's moon , diameter: 3,476 km = 11.6 light milliseconds)
  11. Asteroids , comets (diameter: a few kilometers to several 100 km)
  12. Meteoroids (diameter: from the meter down to the millimeter range)
  13. Dust particles
  14. Molecules
  15. Atoms
  16. Hadrons
  17. Quarks

Note: Some of the size scales listed overlap one another. For example, there are moons that are larger than planets, asteroids that are much larger than some moons, etc. In fact, the classification of celestial objects due to their size is currently very controversial in astronomy, for example the question of which solar satellites belong to the planets should and which not ( Pluto , Plutinos , Transneptune etc.).

exploration

Temperature fluctuations in the background radiation recorded by the WMAP satellite (mission from 2001–2010)

Cosmology tries to create a model of the large-scale structure of our universe. Above all, the Big Bang model and assumptions about the type of matter in the universe are used as a basis. This makes it 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 takes place, among other things, in the context of cosmological simulations . At present, the observations suggest that most of the matter in the universe consists of cold dark matter . Theories that work with hot or baryonic dark matter, on the other hand, do not make good predictions. Other ways of looking at these models are possible on the basis of minimal fluctuations in the cosmological background radiation or with strongly redshifted supernovae . There is a growing consensus that all of these approaches deliver one result: We live in an accelerated universe.

Procedure

Another way of finding out something about the large-scale structure of the cosmos is the so-called Lyman-alpha forest . This is a collection of spectral lines in the light from quasars . They are considered to be a relatively sure sign of the existence of giant interstellar gas clouds (made up primarily of hydrogen ). These gas clouds in turn seem to influence the formation of new galaxies.

When exploring the large-scale structures, the effect of the gravitational lenses must be taken into account. These curve the course of light rays so that the image of an object can lie in a different direction than the object itself. This is caused by objects in the foreground (e.g. galaxies) which (according to the general theory of relativity ) bend the space in their surroundings and thus deflect the rays of light. Powerful gravitational lenses are even useful because they can enlarge distant galaxies, making them easier to discover. The weak gravimetric shear caused by the universe between the source and the observer can, however, significantly change the observed structure and thus make observation more difficult. This shear in turn can be used to verify various cosmological models.

Problems

The large-scale structure of the universe is, however, not realistically represented by the sole use of the redshift to determine the distance. For example, galaxies behind a cluster would be attracted to it and thus be slightly blue-shifted (compared to the situation without the cluster). In front of the cluster, however, the galaxies would be slightly redshifted. The environment of the cluster would appear a bit flattened. An opposite effect can be observed in the galaxies in a cluster: These have random movements around the center of the cluster which - when converted into a redshift - result in a stretched image. This creates what is known as the " finger of God ": the illusion of a whole series of galaxies pointing to Earth.

See also

literature

  • Structure of the cosmos . Worldviews from Hoyle to Hubble. Stars and Space Dossier, No. 2006/1 . Spectrum of Science, ISBN 978-3-938639-34-4 .

Web links