The matter of the Universe is ordered. The force of gravity makes matter clump together into structures. From the simplest, such as stars or solar systems, to gigantic walls of galaxies.
Even so, the expansion of the Universe causes the different structures to move away from each other at great speed.
The most distant structures are the largest and oldest. They were formed when the Universe was still very young, and they help to know its evolution.
Structure hierarchy
Minor structures: they are celestial bodies, such as planets and stars, and small groups, such as our Solar System.
Galaxies : they are intermediate structures. They group families of stars, gas, dust, and dark matter. Only in the visible universe there are more than 100,000 million, and they can group billions of stars. Many have a black hole at their center. Our galaxy is the Milky Way.
Clusters of galaxies: they are groups of galaxies wrapped in hot gas. Its diameter reaches several million light years.
Galaxies revolve around each other, held together by gravity. Sometimes they collide or absorb each other. The Milky Way belongs to a cluster called the Local Group, made up of 25 galaxies.
Superclusters of galaxies: They are groups of galaxy clusters. They measure hundreds of millions of light years. They form great layers throughout the visible Universe. The Local Group is part of the Virgo Supercluster.
Walls: these are the last discovered structures, the oldest and largest in the Universe. They form huge fringes of superclusters of galaxies.
Sloan’s Great Wall, pictured, measures 1.37 billion light-years. In November 2013, the largest known structure was discovered, the Great Wall of Hercules-Corona Borealis , which is located 10,000 million light years from Earth and has dimensions of 10,000 million light years from one end to the other; 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 advance towards a mysterious point called the Great Attractor. Its center is 150 million light years away. It was discovered in the late 1980s 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).
