Galaxies are thought to have been formed roughly 13 to 14 billion years ago. For example, our Milky Way, like many other spiral galaxies, has a linear, starry bar at its center. This usually can cause matter in the disk to take on a distinctive spiral shape, like a cosmic pinwheel. The spinning motion reaches speeds of up to hundreds of kilometers/miles per second. They have a flat, spinning disk with a central bulge surrounded by spiral arms. Observations revealed that spiral galaxies were the most common type of galaxies found throughout the universe. He grouped them into four main categories: spiral galaxies, lenticular galaxies, elliptical galaxies, and irregular galaxies. With this revelation further studies were conducted, many other galaxies were discovered and in 1936, Hubble debuted a way to classify galaxies. All of this changed in 1920 when astronomer Edwin Hubble demonstrated that the Andromeda nebula was, in fact, a galaxy. Galaxies were first classified as nebulae since they looked like fuzzy clouds. In fact, we didn’t even know that other galaxies existed, other than the Milky Way for a long time. The discovery of other types of galaxies is fairly recent. Spiral galaxies tend to be the brightest galaxies in the universe.Most spiral galaxies contain a supermassive black hole in the center of the central bulge.Spiral galaxies are mostly found in low-density regions, and very rarely at the center of galaxy clusters.Around 60% of the observable universe is comprised out of spiral galaxies. Spiral galaxies are the most common type of galaxies found throughout the Universe.Our Milky Way, for example, is a barred spiral galaxy.This bar extends from the central bulge at the ends of which spiral arms begin.Around two-thirds of all spiral galaxies have an additional component in the form of a bar-like structure.
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