The STRUCTURE of the UNIVERSE

We shine a light on the vast network of galaxy clusters and filaments that cross the universe. Our galaxy does not sit alone in isolation in space. This is the structure of the cosmos. The region around the Milky Way galaxy is rather crowded. Together with the Andromeda galaxy, our nearest neighbor, the Milky Way belongs to a group of 30 galaxies and dwarf galaxies called the local group. This collective structure is also part of a larger structure, a number of nearby groups and clusters that make up the Virgo supercluster. This stretches over hundreds of millions of light years and is just one of many superclusters in the known universe. These superclusters are linked with a thread-like filament of galaxies. Galaxies are not scattered through space randomly. They adhere to a web-like pattern that is formed under the influence of dark matter. This web-like structure creates filaments and between that is near empty voids. The characteristics of this cosmic web were set in the aftermath of the Big Bang. Tiny variations in density within the Big Bang imprinted a dark matter patchwork that has been reinforced by billions of years of gravitational interactions. The gas followed the dark matter, creating the galaxies and stars that we know today. The distances to the various members of the local group can be determined by measuring redshift, where the light from galaxies that are moving away appears to have longer wavelengths. Another method is variable stars. This is a pattern of fluctuating intensity and this allows astronomers to calculate their intrinsic brightness, allowing their distance to be calculated. The Milky Way, our home galaxy, is a barred spiral galaxy that is over 100,000 light years in diameter and contains at least 200 billion stars. It lies close to the center of the local group and is orbited by the large and small mineralogic clouds. A host of galaxies also populate the local group, the smallest of which are just a few thousand light years in diameter. There may be more dwarf galaxies around the Milky Way that have eclipsed detection. It is difficult for astronomers to spot these objects because they're behind foreground stars and dust clouds and not forgetting the core of the galaxy itself. A number of dwarf galaxies have already crashed into the Milky Way. They're stars and gas mixed in as a result. Some astronomers claim to have seen remnants of these galaxies as tails in the spiral structure of the Milky Way galaxy. The mineralogic clouds are among the Milky Way's nearest neighbors. The large mineralogic cloud lies about 180,000 light years away and the small mineralogic cloud is around 200,000. A stream of hydrogen called the mineralogic stream is drawn out by past interactions with the Milky Way galaxy and this is what connects the galaxy to the clouds. Their orbits suggest that we may be seeing them at a time when they're unusually close. In 1987 the large mineralogic cloud was host to the brightest supernova observed in four centuries. The supernova was named SN 1987A. The Andromeda Galaxy M31 is a spiral galaxy just like our very own Milky Way. It's 2.6 million light years away from us and contains around a trillion stars, about five times the number of our Milky Way, making it the largest member of the local group. But it may not be as massive as you think. Astronomers have shown that it contains less dark matter than the Milky Way. M31 is also one of very few galaxies approaching the Milky Way and it will collide with us within four billion years. Two main members sit at the core of the local group, the Milky Way and the Andromeda Galaxy. Both spiral galaxies are hundreds of thousands of light years in diameter. 30 or so smaller companions are scattered within a region of 10 million light years and dwarf galaxies surround the two primary members. Being so busy, the local group is a very dynamic place and the Triangulum Galaxy M33 is a highly wound spiral galaxy and is the third largest member of the local group. It is also the most distant visible object without optical instruments, even though it's over three million light years away. It can still be seen with the naked eye. Part of its beauty comes from the fact that it's so rich in clouds of molecular gas and many stars are forming within it. When astronomers mapped the positions of millions of galaxies, they saw that they were not scattered randomly through space, but followed patterns. Galaxies mostly lie on the surface of many bubbles in a kind of cosmic foam. This foam can be seen in slices, revealing blocky walls and long filaments of galaxies surrounded by relatively empty voids. Astronomical surveys use redshift measurements to induce distance. Galaxies that are further away appear redder as light traveling from them is scattered due to the expansion of the universe. One of the first galaxy structures detected was the Great Wall. This is a sheet of galaxies that is hundreds of millions of light years thick. Since then, better telescopes and instruments have revealed vast areas of the cosmic web. There are many types of galaxies. Elliptical galaxies favor the densest of regions in the heart of galaxy clusters that lie in the intersection of filaments. Spiral galaxies, on the other hand, are more of a delicate type of galaxy. These galaxies are spread more widely and can be seen in less dense areas. Some spiral galaxies even pop up in barren voids. It is theorized by many astrophysicists that void galaxies are the result of a large galactic filament being pulled apart by gravity. Galaxies just like this one have been left behind to live out their life alone. Regions with many collisions churn out elliptical galaxies, while more sedate areas can support spirals. Superclusters are the most galaxy-rich regions in the universe. Over 90% of all galaxies in the universe live within these regions. They are composed of chains, each containing hundreds of thousands of galaxies, as well as surrounding filaments, and can extend for hundreds of millions of light-years. The Milky Way and its local group are part of one such galaxy collection, named the Virgo Supercluster. Other nearby examples include the Coma Supercluster and the Hydra Supercluster, as well as a giant Perseus-Pisces Supercluster. All these superclusters are around 200 million light-years away. Redshift surveys show where most of the galaxies are, but the universe is made up of mostly dark matter. Dark matter is thought to largely trace the same patterns of the galaxies. It surrounds all the filaments, walls, and clusters. Most of it lies in clusters and superclusters, accounting for hundreds of times the mass of the stars in those vast systems. Astronomers are trying to search for clumps of dark matter within clusters, by looking for its gravitational influence on nearby galaxies. They can also test theories using computer simulations. Dark matter is divisible by its various types. If dark matter originates in energetic and fast-moving particles, the dark matter is known as hot dark matter. If this is the case, then small-scale galaxy clusters should become less defined over time. If dark matter is known to be cold, then the structures should be retained. This terminology of hot and cold is not meant to be confused with temperature, but instead it refers to the size of the particular dark matter particles, and the size of these particles determines the velocities at which they travel. Using computer simulations, astronomers can model whole galaxy filaments, walls, and clusters. The story begins in a hot young universe. Some regions become slightly more dense than others, creating seeds that later form galaxy structures. By accreting surrounding material through gravity, these faint structures glow more and more massive. Then filaments and blobs start to form in the universe's matter and dark matter. It's dark matter's web-like blueprint that dictates where galaxies and stars form. Once this happens, filament streams start to intersect, and clusters emerge and concentrate. And as the universe ages over billions of years, these superclusters grow. According to this theory, it is the largest structures that are latest to emerge in the universe. So there should be relatively few massive clusters in the young universe, a trend that astronomers have yet to establish through observations. So I hope you've enjoyed the video on the structure of the cosmos. If you'd like to know any more about this subject, I'll put some links in the description below. And of course, if you've enjoyed the video, click the like button, and if you'd like to support the channel, click subscribe, or support our Patreon. And as always, thank you for watching.