Barred-galaxy types usually have spiral arms that are tightly wound. This means that in our central region, we have a large bar near the nucleus where the spiral arms (one contains our solar system) branch out from. The Milky Way was long thought to merely be a spiral galaxy, but recently, we found that the Milky Way is actually a barred spiral galaxy. There are ordinary spiral galaxies and barred spiral galaxies. Oddly enough, this classification has two flavors. The material is organized in a way that is conductive to star formation, as something called "density waves" cause the material to circulate through the spiral arms like circling waves, where they ultimately squeeze and collapse, giving life to new stars. Some of their arms can extend several hundreds of thousands of light-years across (the Milky Way is about 100,000 light-years across, all in all), and they have stars of various ages scattered about. They have bright central regions, where intricate filaments of stellar materials extend from. Galaxies of this type tend to be structured similar to a pinwheel, with a large central bulge, expansive disks, and a halo. Our galaxy, and our closest neighbor (Andromeda), are among this type. During these mergers, many massive stars are formed, which typically live fast and die hard, ejecting mass quantities of heavy metals into the interstellar medium. The massive size of galaxies of this type can be attributed to several galactic mergers, an event prone to advancing star formation activity. In addition to this, they don't contain many star forming regions, as they have used the bulk of their stellar material early in their formation. Generally, galaxies of this type are older and have no overly defined structure (they usually resemble an American football, and are about 6 million light-years across). "So what other kinds of galaxies are there," you might ask? Here are the main types:įirst and foremost, we have elliptical galaxies: the largest (and arguably most dull) of the bunch. With that revelation, we've learned that galaxies come in all shapes and sizes too. Almost 100 years later, our reality (and relative insignificance) is well known, as we are now aware of the fact that the universe contains several BILLION large galaxies, many of which are similar to our own (current estimates guess that there are 100 to 200 billion galaxies in the Universe). nebula debate in 1925, and it was finally revealed that this "nebula" was actually a galaxy containing some 400 billion stars and not simply an extension of our own galaxy. It wasn't until the early 1900's that the nature of the so-called "Andromeda nebula" was discerned. All we could see was our own little corner of the universe. Surprisingly, over the course of most of humanity's existence, we had no idea that other galaxies even existed.
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