Galaxies are a collection of bodies that include stars, planets, and dust bound together by gravity. The word galaxy originates from the Greek word for "milky," which was used to refer to the Milky Way galaxy. The Orion arm of the Milky Way galaxy is where our solar system is located, and like most galaxies, scientists believe there is a black hole at its center. Galaxies are classified into three main types: elliptical, spiral, and irregular. The exact number of galaxies in the universe is has not been determined, although estimates suggest there are between 200 billion and 2 trillion galaxies, the oldest of which is GN-z11. Edwin Hubble established the system used to categorize galaxies.
Types of Galaxies
Elliptical galaxies are usually spherical, and are formed by smaller galaxies colliding into one another. The galaxies are diverse and vary immensely in size, with some having as many as a trillion stars. They do not have an intricate structure, but instead, the stars erratically orbit the galaxy's center. Within elliptical galaxies, very few new stars are formed because they contain very little gas or dust. The stars within elliptical galaxies are usually older, with some being at least a billion years old, and tend to produce red light. Scientists initially thought elliptical galaxies evolved into spiral galaxies. However, this was proven to be false. Giant elliptical galaxies like the M87 have supermassive black holes at their center, which scientists theorize could have a mass equal to at least a billion suns.
Spiral galaxies are named after the spiral shape formed by their arms. The Milky Way and galaxies are some of the most well studied spiral galaxies, while BX442 is the oldest. The arms of spiral galaxies are distinct because they are made up of young stars producing a lot of bright light, gas, and dust. Scientists are yet to accurately determine how the arms are formed because Bertil Lindblad proved that it was highly improbable that the stars would be eternally set in a spiral. The center of the galaxies is made up of a dense collection of older stars with what scientists believe to be a supermassive black hole at the center.
Galaxies that do not belong to any specific class are classified as irregular. They are hotbeds of star formation due to the vast quantities of dust and gas within them. Irregular galaxies are the most diverse classification, but the least prevalent in the universe since they make up at most only a quarter of the total observed galaxies. The formation of irregular galaxies may be due to collision with other galaxies or the impact of gravitational forces.
James Webb Space Telescope
The James Webb Space Telescope is the latest telescope being developed to take over from the Hubble Space Telescope. It will be the most powerful telescope ever built, and will allow scientists to look further into the universe than was previously possible. Scientists are also hopeful that they will be able to use the telescope to see the origin of the first galaxies.
About the Author
Benjamin Elisha Sawe holds a Bachelor of Arts in Economics and Statistics and an MBA in Strategic Management. He is a frequent World Atlas contributor.
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