8/28/2023 0 Comments Elliptical vs spiral galaxy![]() Giant ellipticals are a few million mega-parsecs across!!!!! Recall how much trouble we had just talking about parsecs being large. If you look at the end of a football, it looks round, but if you look at it from the side, it is elongated.Įllipticals can also be sorted by size. However, projection effects (which side of the galaxy you are looking at-the short end, or the long side) can be important. This subclassification is much less arbitrary than the subclassification of spirals, because you actually measure the axes to determine the subclass. E0 are the roundest type, whereas E7 are the most elliptical. They are just big blobs of reddish, older stars. ![]() Once again, these sub-classes indicate the relative size of the bulge.Ģ) Ellipticals: Elliptical galaxies have no arms, no disk. The barred spirals are also subdivided into three classes, SBa, SBb, and SBc. Some people group barred spirals and spirals together in the same group. A type Sc galaxy (Spiral c) has a small bulge, and very prominent arms.Ī barred spiral is very much like a spiral, except that the bulge is elongated, forming a bar across the center. A type Sa galaxy (Spiral a) has a large bulge, and tightly wound arms. These classes roughly indicate the size of the bulge relative to the galaxy. Spirals are subdivided into classes a, b, and c. This means that the same physical principles are probably operating in galaxies as in our solar system! How about that! The whole thing is analogous to our solar system, which has a disordered massive center (the Sun), an ordered disk (the ecliptic), and a disordered outer cloud (the Oort Cloud). These stars can orbit the center in either sense, or with any inclination to the disk. The stars in the halo and the bulge, however, travel in disordered orbits. All of the stars travel around the bulge in the same "sense" (clockwise, or counter-clockwise). ![]() The stars in the disk orbit the center of the galaxy in an ordered fashion. Why? Because star formation occurs in gassy, dusty places! Without knowing anything else, you might think that this means that there is a lot more dust and gas in the disk than in the bulge or the halo, and you'd be right. The bulge and the halo are both composed of reddish, older stars, but the disk and the arms are composed of bluish, younger stars. ![]() There are 3.5 types of galaxies that we observe:ġ) Spirals: Spirals consist of a bulge, a disk (with arms), and a halo. Even though the dust and gas occupy more space in a galaxy, the stars contribute far more to the mass. Galaxies are basically big clusters of dust, gas, and stars. Introduction to Astronomy Normal Galaxies ![]()
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