Types of Galaxies
Last time I talked about the Great Debate of 1920, and about Edwin Hubble’s discovery that Galaxies lie beyond the Milky Way. The 1920s changed over view of the Universe – they made it much larger! This time I’m going to quickly outline the basic types of galaxies and the kind of sizes and distances we are dealing with.
Galaxies are usually grouped by their appearance. You may be familiar with spiral galaxies, for example. In fact there are two types of spiral galaxy: those with bars through their middle, and those without. You also have elliptical galaxies, which are basically big blobs of stars. Finally there are irregular galaxies, i.e. galaxies that don’t seem to be one shape or another really. There are examples of each of these types shown below – taken from the Galaxy Zoo data, of course!
The different shapes of galaxies tell us something about their properties, and we’ll deal with each type of galaxy in the next few blog posts. For now I thought I’d end with another of Hubble’s ideas. When he saw these different types of galaxies he tried to understand the different shapes as an overall evolution. He thought that elliptical galaxies might evolve into spirals as time went by. The Hubble ‘tuning fork’ diagram is shown below.
Hubble called the elliptical galaxies ‘early’ galaxies and the spirals ‘late’ galaxies. Galaxies do not move left across the diagram as they evolve, but still the diagram is a nice way to visualise the varying shapes of galaxies relative to one another. Understanding the shapes – or morphologies – of galaxies are a huge part of the motivation behind the Galaxy Zoo project. you can learn more about it on our science pages.
[UPDATE: This post has been modified from its original form to correct some errors on my part.]