Types of galaxies

A project to create a fictional astronomy for Shireroth and its world
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Shyriath
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Types of galaxies

Post by Shyriath »

Since what kind of sky we have is going to be affected by what kind of galaxy we're in, perhaps we ought to consider the issue. I'm compiling a list of possible galaxy types in this thread to aid in this, and for general infotainment.Elliptical: A type of galaxy consisting of older, redder stars, with relatively little new star formation. Contain little interstellar matter, no open star clusters; relatively uniform distribution, though they're probably more packed together toward the center. Can range from spherical in shape to long and thin. Range considerably in size, from some of the largest galaxies in the universe, to the tiny dwarf ellipticals found orbiting other galaxies. The larger ones often have globular clusters orbiting them.Although traditionally considered to be older galaxies that formed all its stars at once, it is now thought that they may be the result of galaxies colliding and and fusing into a larger mass, as sort of a snowball effect; although consisting mostly of older stars, they get occasional infusions of younger ones through the fusing process.Lenticular: Somewhere between an elliptical galaxy and a spiral galaxy, takes the form of a flattened disk with a central bulge, but without distinct arms. Like elliptical galaxies, tend to have little interstellar matter and more older stars.Spiral: These boys consist of a central bulge (made up mostly of older stars, and by themselves resembling elliptical galaxies) surrounded by a disc of younger, bluer stars, concentrated into "arms" spiralling out from and around this core. This effect is believed to be a wavefront effect where the elliptical orbits of the various stars making up the disk happen to coincide. The disk tends to be relatively rich in interstellar matter and open star clusters, and most stellar formation takes place there. Beyond the disc, orbiting the galaxy, there are often globular star clusters or other spherical star formations.Most spiral galaxies, it is believed, have a supermassive black hole at the center. Spirals tend to be larger galaxies, and vary less in size than do ellipticals. The arms can be loosely or tightly wound, can be longer or shorter, and can vary considerably in how distinct they are.Barred Spiral: Generally similar to spiral galaxies, they are distinguished from them by the elongated shape of their central bulges. Instead of having a more spherical core, the central bugle instead forms a short bar, from the ends of which the arms extend. This is believed to result from a density wave phenomenon, presumably somewhat similar to that which creates the arms.Unlike the more sedate cores of "normal" spirals, barred spiral galaxies often have cores with active regions of star formation; the bar is believed to funnel gas into from the spiral arms, bringing a flow of new material into the core.Barred spirals are as common as, if not more common than, "normal" spirals in most sky surveys, making up two-thirds of the galactic population. Because bars are believed to be fairly temporary, unstable structures, this suggests that bar formation is a reoccurring phenomenon. Recent infrared observations by the Spitzer Space telescope suggest that our own Milky Way, long assumed to be a regular spiral, or having only a small bar, may in fact be a full-fledged barred spiral galaxy.Ring galaxy: Somewhat similar to a spiral galaxy, but instead of the bulge being surrounded by a disk composed of arms, it is orbited by a detached ring of younger stars. It is believed that this is caused by the passage of a smaller galaxy through the center of a larger one.Irregular: Galaxies that have little to no structure, often chaotically-shaped. Some of them do retain noticeable spiral structure, which suggests that at least some irregulars were galaxies of other types that were deformed by the gravitational influence of other galaxies.The so-called dwarf irregulars are a subset of the irregulars noted for their high proportions of gaseous elements and low proportions of metals, and are believed to be similar to the earliest galaxies. Many (most?) irregulars, however, are composed of young, blue stars, and contain ample gas and dust for new stars to form. Edited by: Shyriath  at: 11/13/05 18:22

UEC
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Re: Types of galaxies

Post by UEC »

mmmm.. *Remembers his Astronomy class last year* quazars...Also about rings. I believe there is a theory that they are caused by a Blackhole at their center eating up the inside... but not having the force to grab the outer ring... E. Metzler (UEC)Duke of Brookshire"Never use a BOO/\/\ist as a diplomat" -- GSClicky Clicky..., Tiss for your own good ya know.Edited by: UEC  at: 11/14/05 13:04

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Fax Celestis
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Re: Types of galaxies

Post by Fax Celestis »

I think the Spiral and Ring formations hold the most potential. Viatax Sitadi Axdivijink Regigoraauk

Shyriath
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Re: Types of galaxies

Post by Shyriath »

It would be pretty spectacular to live near a quasar, although I think our poor planet would get fried... pity......but yes, either spiral or ring will work. Especially since, if we're assuming that our solar system is in the disk/ring portion, the view of the galaxy will look pretty much the same in the night sky either way: a band of light in the sky.If we want to make things more interesting, we could make it less like our view of the Milky Way by saying that the solar system is nearer the edge of the galaxy. The band of light would either fainter or faded to nothing in part of the sky... and that would provide a fertile ground for astronomy-related myths, I think.

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