Galaxy clusters and large structures

Just as stars come together to form galaxies, the galaxies themselves can also form a structure. Galaxies that move in a common gravitational field form so-called galaxy clusters. Up to several thousand galaxies can be gravitationally linked in this way and form clusters up to 10 million light years across. Clusters of galaxies are permeated by gas. This gas is several million degrees Kelvin hot and emits X-rays that researchers can detect (a typical example of X-ray astronomy). The gas and the galaxies together form only about 20% of the mass of a cluster. The rest consists of dark matter.
Galaxy clusters have different shapes - so-called morphological types, similar to the types of galaxies. However, it is much more difficult to define a classification than for galaxies, and none has as yet become established as a standard.
The galaxy cluster in which the Milky Way and, consequently, our own Sun and the Earth are located is called the Local Group.
Superclusters, filaments, voids and large quasar groups
Galaxies are not evenly distributed in the universe. In some places there are more of them, in others hardly any, and they form a honeycomb-like structure. So-called galaxy superclusters are formed where the "walls" of such honeycombs intersect (i.e. where many galaxy clusters accumulate). They have a diameter of several hundred million light years.
It was previously assumed that the Milky Way is part of the Laniakea supercluster, which spans approximately 520 million light-years and contains around 100,000 other galaxies. Recent research suggests, however, that Laniakea might not be a distinct structure but rather part of the Shapley supercluster. See the link on the right for more information.
The empty spaces in the honeycombs are called voids. Filaments also run between the galaxy clusters and superclusters. These are connecting "threads" of gas, dark matter and individual galaxies.
An even larger structure than this honeycomb shape is now known: large quasar groups. Quasars are the active nucleus of a galaxy. These are regions that emit very large amounts of radiation. This radiation comes from the accretion disk that surrounds a black hole. However, quasars look more or less like stars, which is why they received their name: quasi-stellar radio sources. If several quasars accumulate, they form a large quasar group - the largest structure known in the universe today. The record is held by U1.27 with 73 quasars, an average diameter of 1.5 billion light years and a maximum expansion of 4 billion light years.
Scientists are working hard to gain a better understanding of how the structures described above came about and how they function. For example, it is not yet clear whether they form superclusters solely due to gravity, or whether other forces play a role.