Metagalaxy

(redirected from metagalaxies)
Also found in: Dictionary.

metagalaxy

[¦med·ə′gal·ik·sē]
(astronomy)
The total assemblage of recognized galaxies; essentially this represents the entire material universe.

Metagalaxy

 

the totality of stellar systems (galaxies), a part of which is the great multitude of galaxies (about 1 million) accessible to modern telescopes. Our galaxy, or the Milky Way System, is one of the stellar systems in the metagalaxy. The metagalaxy has sometimes been unfortunately referred to as the Great Universe. An ever-increasing region of the metagalaxy is becoming accessible to observation with the increasing power of telescopes (some scientists refer to the metagalaxy as solely the region accessible to observation).

The actual investigation of the metagalaxy became possible during the 1920’s, when scientists succeeded in proving, using the largest telescopes then in existence, that many previously known bright nebulae whose stellar nature had long remained in doubt are in fact gigantic stellar systems similar to our galaxy.

Detailed investigation of extragalactic objects has resulted in the discovery of different types of galaxies, in particular, radio galaxies and quasars. Individual stars, as well as intergalactic gas, cosmic rays, and electromagnetic radiation, are found in the space between the galaxies. Cosmic dust may sometimes be found within clusters of galaxies.

The mean density of matter in the part of the metagalaxy known to us has been estimated by different scientists to be between 10~31 and 10~30 g/cm3. However, marked local inhomogeneities, sometimes large-scale, associated with the presence of structured formations within the metagalaxy are observed. Many galaxies show groupings of different degrees of complexity—binary and more complex multiple systems; clusters containing tens, hundreds, and thousands of galaxies; and clouds containing tens of thousands of galaxies and more. Thus, for example, our galaxy and the 15 nearest galaxies to it are members of a small cluster called the local group of galaxies. The local group apparently belongs to a gigantic cloud in whose central core is a cluster that contains several thousand galaxies and is visible in the constellations Virgo and Coma Berenices at a distance of 12 to 14 million parsecs (about 40 million lightyears) from us.

Nothing is yet known regarding the dimensions, form, and structure of the metagalaxy as a whole. The distribution of galaxies (on the scale of the entire known part of the metagalaxy) does not reveal any systematic decreases in density in any direction, which would indicate an approach to the boundaries of the metagalaxy. The absence of any such decrease in density seems to show that the region known to us is relatively small in comparison with the dimensions of the metagalaxy. Whatever these dimensions are, the metagalaxy must be considered as an enormous but finite aggregate of galaxies possessing over a long period of time certain distinctive features of structure and motion. Such features may include the mutual recession of the galaxies composing the entire metagalaxy or a part of it. Thus the metagalaxy constitutes a finite and transient structured formation in an eternal and infinite universe that contains, in particular, an uncountable number of galaxies.

B. A. VORONTSOV-VEL’IAMINOV