• Question: Why are galaxies much wider than they are high?

    Asked by lizzie3006 to Ben, Jony, Katharine, Mark, Peter on 21 Nov 2011. This question was also asked by tatexoxoxo.
    • Photo: Ben Still

      Ben Still answered on 21 Nov 2011:

      Spiral galaxies, like our own Milky Way, are like this but there are other shapes of Galaxy. Spherical for instance are called spherical because they are pretty much ball shaped, and so are pretty much as high as they are wide. There are many other classes of galaxy too.

      The reason spiral galaxies are flat across a disk is the rotating motion of the gas that initially formed the galaxy, the rotation acts to spread out the gas/stars along the plane in which the galaxy is rotating. If you have ever seen a pizza chef spin a pizza base then this is a similar effect. Starting with a thick piece of dough it is spun in the air and the dough stretches and flattens – but there is always gravity acting in the opposite making sure that it doesn’t get too thin and flat. It is a balance between this rotational force and gravity that determines the flatness of the galaxy.

      Pizza spinning video: http://www.youtube.com/watch?v=HWL__9yDu8I&feature=player_embedded#!

    • Photo: Peter Williams

      Peter Williams answered on 21 Nov 2011:

      in short – rotation

      some of them aren’t – they can be pretty much spherical, or elliptical or the classic spiral shape or anything inbetween.

      If there is a net angular momentum in the galaxy, it will flatten out along the plane perpendicular to the angular momentum vector.

      One interesting aspect of this is it is how dark matter got discovered by Fritz Zwicky in 1933. The speed of rotation of galaxies is faster than you would expect from the amount of luminous matter in them, So there must be something extra that you can’t see that provides the extra gravitational pull – dark matter

    • Photo: Mark Basham

      Mark Basham answered on 21 Nov 2011:

      Excellent answers from the other guys here, But if you like Galaxies, then you might want to check out Galaxy Zoo, which lets you help scientists out by classifying galaxies for them 🙂

      http://www.galaxyzoo.org/

    • Photo: Jony Hudson

      Jony Hudson answered on 21 Nov 2011:

      What they said ^^^ !

      Nice link Mark, hadn’t seen that before 🙂

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