![]() Completely spherical elliptical galaxies are referred to as E0 types, flattening out to more oval or American football-shaped galaxies as E1, E2, and so on all the way to E4. Hubble’s system of classifying elliptical galaxies is not based on size, spectrum, or origin but rather on shape and structure (more commonly referred to as morphology). By contrast, dwarf elliptical galaxies are frequently found circling larger spiral or elliptical galaxies. Giant elliptical galaxies make up some of the largest galaxies in the Universe. This is probably the only classification you’ve ever heard of, but it’s a little incomplete.Įlliptical galaxies are galaxies with little dust and gas left. He came up with a system that is still used today. In 1926, around the same time that it was proven that the odd “spiral nebulae” in the sky and some of the other “faint fuzzies” seen through telescopes were actually separate galaxies or “island universes” from our own, astronomer Edwin Hubble sought to classify these objects. Origins of Galaxy Types & Classification Hubble’s Sequence of Galaxies The galaxies we’ve listed in each category are those that we’ve picked because they show the defining feature of their given morphological type many other well-known galaxies fit into each type we’ve listed. This article will give an overall layout of the classification and known types of galaxies, as well as some you can observe yourself with a fairly modest telescope under suburban or dark skies. However, there are quite a few exotic types, some of which can be observed with backyard telescopes, and numerous intermediate classifications and variations between the most commonly described galaxy types. ![]() You may have heard of the classes of spiral, elliptical, and irregular galaxies, along with perhaps lenticular galaxies, too. Galaxy evolution is a far more complex process than Hubble imagined, involving the conditions of the galaxy's initial collapse, collisions with other galaxies, and the ebb and flow of internal star birth.There are many more types of galaxies than common thinking might suggest. ![]() Hence "Sa" and "SBa" galaxies were called "early-type," while "Sc" and "SBc" were called "late-type."Īstronomers still use this nomenclature today, though the initial concept was later found to be an over-simplification. Those include irregular galaxies which have odd shapes, dwarf galaxies which are very small, and giant elliptical galaxies which are very large elliptical galaxies residing in the centers of some clusters of galaxies.įor a time the Hubble tuning fork was thought to be an evolutionary sequence - that galaxies might evolve from one type to another progressing from left to right across the tuning-fork diagram. Hubble found that some galaxies are difficult to put in the context of the tuning fork diagram. "S0," or lenticular galaxies, are in the transition zones between ellipticals and spirals and bridge these two types. An "SBc" is thus a loosely wound barred spiral galaxy. Barred spirals have a "B" in their classification. The spiral arms in barred spirals usually start at the end of the bar instead of from the bulge. The most important difference between these two groups is the bar of stars that runs through the central bulge in barred spirals. In fact the spiral galaxies are sub-divided into two groups - normal spirals and barred spirals. There are indications pointing to a very close connection between the bulges of certain galaxies (Hubble types "S0", "Sa" and "Sb") and elliptical galaxies. ![]() Also it is worth noting that the sizes of the round central regions in spirals - the so-called bulges - increase in size the more tightly the spiral arms are wound. ![]() "Sa" spirals, for example, are tightly wound whereas "Sc" spirals are more loosely wound. The spirals were assigned letters from "a" to "c," which characterize the compactness of their spiral arms. Hubble gave the ellipticals numbers from zero to seven, which characterize the ellipticity of the galaxy - "E0" is almost round, "E7" is very elliptical. The diagram is roughly divided into two parts: elliptical galaxies (ellipticals) and spiral galaxies (spirals). Although this scheme, also known as the Hubble tuning fork diagram, is now considered somewhat too simple, the basic ideas still hold. As one of the first steps towards a coherent theory of galaxy evolution, the American astronomer Edwin Hubble, developed a classification scheme of galaxies in 1926. Some are simple, while others are very complex in structure. Galaxies are very important fundamental building blocks of the Universe. ![]()
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