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!

spirals

Spirals

barredspirals

Barred Spirals

ellipticals

Ellipticals

irregulars

Irregulars

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.

HubbleTuningFork2w

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.]

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9 responses to “Types of Galaxies”

  1. Joseph K. H. Cheng says :

    A nice update on galaxy morphology and a good revision on Hubble’s theory

    JKHC.

  2. Carlos Gama says :

    “There is no way that elliptical galaxies could spontaneously begin rotating faster and faster”.

    Isn’t this assertion a bit premature to say the least, as we don’t yet fully understand how the Universe really works. Isn’t this the same as saying “There is no way the Universe could spontaneously begin expanding faster and faster”? Well AFAIK the last time we checked it really is! Isn’t this the reason we talk about Dark Energy? If there is indeed a yet unknown force in the Universe responsible for the Expansion, couldn’t it also be responsible for accelerating the rotation of Galaxies? I agree that they couldn’t just keep accelerating forever, but what kind of effects can Dark Energy have over how Galaxies evolve?!

  3. John McD. says :

    Couldnt a galaxy pick up speed and spin like when an ice skater pulls in their arms while spinning to increase the speed of the spin. or maybe its like drafting in nascar, once the galaxy has clumped up enough the effect of the spiral arms and closer grouped stars etc acting together builds momentum. I just agree it is too early to say it is impossible for na galaxy to pick up speed somehow over its entire evolution.

  4. Steven says :

    Actually, Hubble did not believe, nor propose, that there was an evolutionary sequence from early- to late-type galaxies. Rather it was a nomenclature borrowed from the classification of stellar spectra, in which the spectra of ‘early types’ have a simple appearance whereas ‘late types’ are complex. The misconception is clearly exposed in this A&G article: http://ukads.nottingham.ac.uk/abs/2008A%26G….49e..25B

  5. Mark Sweetman says :

    Hello.

    I’m actually a firefighter in New Zealand but randomly enough im real interested in Galaxies ect. But i was really curious as to what this was when i was doing galaxyzoo classifications,

    http://cas.sdss.org/stripe82/en/tools/quicklook/quickobj.asp?id=8647474691933208589

    If you could let me know that would be awesome

    Thank you
    Mark

  6. Dave says :

    Mark S.
    A meteor track or ??

  7. sevda says :

    what are late type and classical dwarf galaxies?

  8. Sayan Som says :

    it’s just so nice

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