Elliptical Galaxies Vs. Spiral Galaxies: What You Need to Know

Elliptical vs spiral galaxies
Their shape and color are not the only things you ought to consider when you pitch elliptical galaxies vs. spiral galaxies to see how they differ from each other. The difference between them goes well beyond these superficial aspects.
Did You Know?
The term 'galaxy' is derived from the Greek word galaxias, meaning milky, with reference to the Milky Way galaxy that our Solar System is a part of.
It is virtually impossible to find the total number of galaxies in the Universe. That shouldn't really come as a surprise, considering that we are yet to ascertain the expanse of the Universe. It is estimated that there are anywhere between 100 - 200 billion galaxies out there. Based on pictures captured by the Hubble Space Telescope, researchers claim that there are a total of 125 billion galaxies; the Milky Way being one of them.
Edwin Hubble's Classification of Galaxies
If you have ever come across facts about the Milky Way, you must be knowing that it's a spiral galaxy ... a barred spiral galaxy to be precise. In 1936, famous astronomer, Edwin Hubble came up with the Hubble sequence, a morphological classification scheme to classify galaxies into three groups on the basis of their appearance: (i) ellipticals, (ii) spirals, and (iii) lenticulars. Of these three, elliptical galaxies, which appeared as ellipses on photographic plates, and spiral galaxies, with their spiral structure, are the most common.
Milky way
The Milky Way: An apt example of a spiral galaxy.
Some of the most popular examples of elliptical galaxies are Messier 32, Messier 60, IC 1101, NGC 50, Maffei 1, etc. On the other hand, some of the best examples of spiral galaxies―other than the Milky Way―are Messier 31, Messier 101, Messier 33, Messier 51a, NGC 253, etc.

Trivia: Even today―78 years after it was introduced―the Hubble Sequence continues to be the most widely used morphological classification scheme for galaxies.
Difference Between Elliptical and Spiral Galaxies
Both, elliptical galaxies and spiral galaxies have quite a few things in common. For starters, both have a halo as a characteristic trait, both have a bulge, and both are found in abundance. And yet, they are quite different from each other; not just in the context of appearance, but also with respect to their content. For instance, did you know that elliptical galaxies do not contain cool gas, as a result of which star formation in them is as good as absent? It is kind of strange, but pitching elliptical galaxies vs. spiral galaxies is your best bet if you are to study their characteristics.
Spiral galaxies
Spiral galaxies can be easily identified by their swirling arms.
As their names suggest, the foremost difference between spiral and elliptical galaxies is that ellipticals appear as ellipsoids―round-to-oval in shape―on photographic plates, while spirals appear as rotating discs with swirling arms (when seen from above) or thin discs with a bulge in the center (when seen from the sides). As opposed to disk-like bulges of spiral galaxies, elliptical galaxies have relatively featureless classical bulges. As far as the brightness is concerned, spiral galaxies are brighter than elliptical galaxies.

While ellipticals have very little or no cool gas and dust at all, spirals are comparatively rich in this aspect. In the absence of cool gas, which is necessary for the formation of stars, the process of star formation is virtually absent in elliptical galaxies. That also explains why elliptical galaxies are largely made up of old, red stars (Population II stars), while spiral galaxies have both, old stars and young, blue stars (Population I stars).

In spirals, it's the disc that is largely made of Population I stars or blue stars, while the bulge, which is devoid of gas and dust, has Population II stars or red stars to its credit. That explains why the bulge is redder than the disc. At the same time, the difference in color also implies that spiral galaxies have continually forming stars in their swirling arms.
Elliptical galaxy and galaxy cluster
Elliptical galaxies are usually found in clusters.
Spiral galaxies are usually found in the low density galactic field, whereas elliptical galaxies are usually found in the high density galactic field. That makes sense because the discs of spirals are very fragile, as such they can easily get destroyed by merging with neighboring galaxies. Even the Milky Way is expected to collide with the Andromeda galaxy in about 4 billion years. As both of them are significantly large, they are most likely to end up distorting themselves.
Despite the fact that we have found more spiral galaxies in the local universe, researchers believe that there are more elliptical galaxies than spirals, or any other type for that matter, in the Universe. If we have found more spirals than ellipticals, it is only because it's easier to spot them.
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