Spiral galaxies are a type of galaxy that was first discovered by Edwin Hubble in 1936 based on their appearance in optical light. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”?Get the original essayA spiral galaxy is shaped like a pinwheel and consists mainly of a flat, rotating disk containing stars, gas and dust. The central point of the galaxy, known as the bulge, is a large star cluster and is also believed to contain a supermassive black hole. These galaxies have arms that extend from the center and rotate around it. These arms consist of a continuous star formation that is brighter than the surrounding disk. The exact formation and mechanics of the spiral arms intrigue scientists. If the arms were permanent features of the galaxy, they would disappear and coil tightly within a billion years. Scientists think this could be the result of density waves passing through the outer disk. About 77% of all galaxies are spiral galaxies, including the one we live in, the Milky Way. Spiral galaxies vary in shape. About 60% of spiral galaxies have multiple arms, about 10% have two, and about 30% of spiral galaxies have no well-defined arms; their characteristics have faded over time. These galaxies are between a billion and a trillion times the mass of the sun. The galaxy's disk can vary from 10 to 300,000 light years. The largest spiral galaxy is 5 times larger than the Milky Way and measures 522,000 light years. Spiral galaxies are divided into two classes: normal spirals and barred spirals. Barred spirals are when the spiral arms come out of a bar passing through the galactic center of the galaxy. When the universe was still young, different galaxies frequently collided and interacted with each other, so the spiral shapes of these ancient spiral galaxies would quickly be disrupted. Keep in mind: this is just a sample. Get a personalized article from our expert writers now. .Get a Custom EssayThe oldest spiral galaxy is almost 10.7 billion years old. Because of the association between time and the distance light needs to travel, scientists are able to see the galaxy only 3 billion years after the Big Bang formed the universe. Once spiral galaxies burn up their gas and dust and star formation slows, they will lose their spiral shape and move on to the next stage of evolution, elliptical galaxies..