The matter of the Universe is ordered. The force of gravity causes matter to be grouped into structures. From the simplest, such as stars or solar systems, to the gigantic walls of galaxies.
Even so, the expansion of the Universe makes the different structures move away from each other at great speed.
The most distant structures are the largest and oldest. They formed when the Universe was still very young, and they help to know its evolution.
Hierarchy of structures
Minor structures: they are the celestial bodies, like the planets and the stars, and the small groupings, like our Solar System.
Galaxies: are intermediate structures. Groups of stars, gas, dust and dark matter group. In the visible universe alone there are more than 100,000 million, and they can group billions of stars. Many have a black hole in their center. Our galaxy is the Milky Way.
Clusters of galaxies: They are sets of galaxies wrapped in hot gas. Its diameter reaches several million light years.
Galaxies revolve around each other, linked by gravity. Sometimes they collide or absorb each other. The Milky Way belongs to a cluster called the Local Group, formed by 25 galaxies.
Superclusters of galaxies: They are clusters of galaxy clusters. They measure hundreds of millions of light years. They form large layers throughout the visible Universe. The Local Group is part of the Virgo Supercluster.
Walls: These are the last structures discovered, the oldest and largest in the Universe. They form huge swathes of galaxy superclusters.
The great wall of Sloan, in the image, measures 1.370 million light years. In November 2013, the largest known structure was discovered, the Great Wall of Hercules-Boreal Crown, which is 10,000 million light years from Earth and has dimensions of 10,000 million light years from one extreme to another; It is very elongated, occupying almost 11% of the observable Universe.
The Great Attractor
The Virgo Supercluster and the rest of the structures of the visible Universe move towards a mysterious point called the Great Attractor. Its center is 150 million light years. It was discovered in the late 80's and it is not yet known what it is, although it could be an even larger structure that astronomers call Laniakea ("immense sky", in Hawaiian).
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