Galaxy clusters


Galaxies are social entities; they rarely appear alone. Since galaxies consist of enormous masses of stars, gas, and dark matter, they attract one another through their gravitational forces, forming groups and clusters.
Since the Big Bang, the universe has been expanding, and all stars and galaxy clusters are moving away from one another. The cosmos is constantly expanding. However, the gravitational force within galaxy groups and clusters is strong enough to hold them together as they drift apart.
Over time, galaxy groups attract additional galaxies, grow, and—over long periods—merge into large clusters containing thousands of galaxies.
Very large groups containing thousands of galaxies are referred to as galaxy clusters. The Virgo Cluster in the constellation Virgo, for example, consists of around 2,000 galaxies. The entire galaxy cluster spans an apparent size of 8 degrees in the sky—making it 16 times larger in extent than the full moon!
Dark matter is an invisible form of matter in the universe that neither emits nor reflects light. It is not directly visible, but it makes itself known through its gravitational force. Without dark matter, galaxies would fly apart, as it acts like an invisible "glue" that holds the stars together.

• Ingredients:
  Galaxy clusters consist of galaxies (of various types, such as spiral, elliptical, or irregular galaxies), hot gas (the intracluster medium, which often emits X-rays), and dark matter, which accounts for the majority of the mass and stabilizes the structure.
• Size and Mass:
  Sie erstrecken sich über Millionen von Lichtjahren und haben typischerweise eine Masse von etwa 10^{14} bis 10^{15} Sonnenmassen.
• Origin:
  Galaxy clusters form through the gravitational attraction of smaller groups of galaxies and matter over billions of years. They are part of the large-scale structure of the universe, which forms a network of filaments, walls, and voids.
• Examples:
  Well-known galaxy clusters are the Virgo Cluster (approximately 54 million light-years away; contains our Milky Way) and the Coma Cluster.
• Meaning:
  They are important for cosmology, as they provide clues regarding the distribution of matter, the expansion of the universe, and the role of dark matter and dark energy.

Dark Matter (Adhesive and supporting Skeleton)
Galaxies orbit one another at very high speeds—up to a thousand kilometers per second. For galaxies to orbit each other at such speeds, a "motor" - that is, a mass - is required that is greater than the mass of the galaxies themselves. Where, then, does this "motive force" - or mass - come from?
There must, therefore, be something that enables galaxy clusters to orbit one another at this speed. Astrophysics refers to this force - or mass - as Dark Matter. It is an invisible form of matter in the universe that neither emits nor reflects light. It is not directly visible, but makes itself known through its gravity. Without dark matter, galaxies would fly apart. Dark matter acts like invisible glue, holding galaxies and stars together like a skeleton.

Dark Energy (The Driving Accelerator)
Dark energy is the term used to describe an effect that explains the accelerated expansion of the universe. Due to gravitational attraction, the expansion of the universe should be slowing down—contrary to what is observed. To explain these observations, dark energy must account for 70% of the total energy and matter in the universe.