There are usually no regions of concentrated active star formation in these galaxies.Ī photograph of the elliptical galaxy M87Įlliptical galaxies are usually found in clusters of other elliptical galaxies. They tend to be smaller and made up of mostly old stars. Elliptical galaxies may or may not be in the shape of a flat disk. Astronomers measure the distance between us and the globular clusters in order to gain understanding about the size and shape of our galaxy.Ī variation of the spiral galaxy with an elongated central bulge is known as a “barred spiral galaxy.”īarred spiral galaxies often may only have two arms, one protruding from each side of the nucleus.Įlliptical galaxies can be oval in shape or spherical. Globular clusters are masses with high concentrations of old stars. Surrounding the disk is a halo of gases where globular clusters near the galaxy reside. The diameter of the Milky Way is about 150,000 light years across, while the width ranges from about 400-2000 light years. Our sun is located about 26,000 light years away from the center of the galaxy (about halfway out) on the arm named Orion. The diameter of the “face of the disk,” if you will, is much larger than the width of the disk. The arms spiral out from the nucleus in such a way that the galaxy is shaped like a frisbee or a flat disk. More young than old stars are found here. The arms are made up of stars, planets, and other celestial bodies. The arms spiraling outward are where active star formation takes place. The nucleus of our galaxy is located near the Sagittarius constellation. The nucleus contains no new stars and no active star formation takes place here. The nucleus is the hottest and brightest part of the galaxy because this is where the highest concentration of energy is located. The nucleus is made up of dust, gas, star clusters, nebulas, and older stars. Research estimates that between 75-85% of galaxies are spiral, including our own galaxy, the Milky Way. Spiral galaxies are composed of three main components: a central bulge called the nucleus, arms twisting outwards from the nucleus, and a halo around the galaxy where globular clusters are located. There are three different categories in which astronomers classify galaxies: spiral, elliptical, and irregular. Today, it is easier to distinguish between nebulas, galaxies, and other celestial bodies. This is from Messier’s nebula classification system. Many nebulas today have named that begin with a capital M followed by a number. He began by cataloging celestial bodies and calling each of the unknown formations “nebulas” until it was deciphered as otherwise. Classification of celestial bodies began with Charles Messier in the 18th century.
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