• Question: Why is dark matter in our universe and what does it do?

    Asked by anon-150745 to Daniel, Hannah, Maggie, Ry, Scott on 9 Nov 2017.
    • Photo: Ry Cutter

      Ry Cutter answered on 9 Nov 2017:

      We don’t actually know if dark matter exists or not!
      The problem is, all the galaxies seem to be spinning faster than their gravity allows. This means there is too much gravity in each galaxy. The only thing that determines how strong your gravity is, is your mass. Which means there has to be some hidden mass adding all this extra gravity! We can’t see it so we call it dark matter.
      Dark matter makes up for all the mass in universe we can’t see. There are loads of theories that try to explain what it is, but we just can’t seem to pin it down.
      It could be that we don’t understand gravity enough and there’s no missing matter at all, there’s a whole other branch of science trying to figure out if that’s true. Dark matter is mysterious and holds a lot of secrets that we’d like to find out.
      Great question,

      Ryan

    • Photo: Maggie Lieu

      Maggie Lieu answered on 10 Nov 2017:

      Dark matter is in our Universe to make the numbers add up.

      Basically if you add up all the stars in a galaxy, there’s still not going to be enough gravity to keep the stars orbiting in the galaxy. Theres not enough mass! So you need dark matter to get enough gravity to keep everything together in a galaxy.

      But dark matter doesn’t do much at all. It doesn’t emit any light so we can’t see it, and it doesn’t interact with anything (even itself!). Take a look at this picture:

      This is called the bullet cluster, and it shows 2 clusters of galaxies crashing into each other. The red colour is hot gas inside the cluster – do you see that the red is much closer together than the blue? This means when the clusters collided, the gas did too and so it slowed down. The blue shows the dark matter (we can only see it from its gravity signature) and you see it passes straight through each other?

      Pretty cool right?

    • Photo: Hannah Middleton

      Hannah Middleton answered on 11 Nov 2017:

      Maggie and Scott’s answers sound good! We have this theory of dark matter because there’s evidence for something that we can’t explain using just normal matter. So we can see the effect of what it does, but we don’t know what it is and why is an even harder question to answer!

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