Other Galaxies

The Milky Way is far from being alone in the Universe. Other galaxies exist, at great distances – the closest full galaxy to us is the Andromeda Galaxy, 2.5 billion light years away – but still visible to our telescopes and observatories. While much is unknown about our distant neighbors, observations have been made about their shapes, their natures, and their origins.

Galaxies exist in multiple types. The best known image of a galaxy is the spiral galaxy, which has beautiful 'arms' that spiral outwards from a central hub. In between the arms there are long lines of dust bridging the gaps. Such galaxies often have a mix of older and newer stars, with new stars still emerging from the dust and gas. Related to the spiral galaxy is the barred spiral, which has a straight 'bar' across the core that spirals only at its ends. Some recent research has revealed that the Milky Way itself may be one of these barred galaxies. The exact nature of the bar is not fully known, but it has been speculated to be the main birthplace of new stars for the galaxy.

One of the most common types of galaxy is somewhat less interesting in shape. Elliptical galaxies form into rough ovals that range in shape from near-circles to elongated 'cigars'. In contrast with spiral galaxies, there tends to be very little gas or dust in an elliptical galaxy, meaning that nearly no new stars form. As a result, elliptical galaxies are populated primarily by old stars. Lenticular galaxies sometimes are seen as well, seemingly halfway between elliptical galaxies and spiral galaxies – they consist mainly of old stars and are fairly stable like elliptical galaxies, but are disc-shaped, contain dust, and have vague spiral arms like spiral galaxies. Scientists believe they might well represent the transition from young spiral galaxies to aged elliptical galaxies as gas and other interstellar matter leave the spiral galaxy, causing the 'arms' to slowly collapse and fade.

The last category is rather broad, encompassing all galaxies that do not fit into the above categories – the irregular galaxies. Irregular galaxies tend to contain mostly young stars, but beyond that they vary greatly from example to example, not forming any standard pattern. Dwarf galaxies are often included in this category – small, irregular galaxies that often orbit other galaxies as 'satellite' galaxies, such as the nearby Magellanic Clouds, which orbit the Milky Way. Often these are disrupted in shape due to the influence of nearby, larger galaxies, which exert a pull that prevents the irregular galaxies from forming a stable shape.

Much still is to be learned about galaxies. Observation suggests that they form around supermassive black holes, but the exact mechanics of this and the resulting birth of stars are fairly unknown. Even our own Milky Way is still a mystery in some respects – it's unsure whether it's barred or not, even. However, as science and astronomy progress, more will be discovered and observed, and soon the mysteries of these objects that dominate the universe will be revealed.




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