• Question: What is the our galaxy made out of? if so, what is our whole universe made out of?

    Asked by chemics to Zachary, Tim, Kristian on 21 Nov 2013.
    • Photo: Zachary Williamson

      Zachary Williamson answered on 21 Nov 2013:

      Hi chemics.

      Our galaxy is made out of a lot of stuff! At its core, our galaxy mostly contains protons, neutrons and electrons, all rearranged into different atomic elements. The most abundant element by far is hydrogen, which makes up 80% of our galaxy’s elements. Helium makes up about 19%, and everything else makes up the 1%.

      However that’s not the whole story, because only 10% of our galaxy’s mass is made up of what we would consider to be ‘normal’ matter (i.e. atoms). 90% of it is called dark matter. Honestly we have no idea what it is, but we can feel its gravitational effects so we know there’s a lot of it out there.

      Our universe is broadly made up of the stuff used to make up our galaxy.


    • Photo: Tim Hollowood

      Tim Hollowood answered on 21 Nov 2013:

      Nice question chemics,

      This is exactly the question that particle physics is trying to answer. We know par of the answer because a small proportional, as Kristian says about 10%, is normal matter, the kind that we are made of. And we know that this consists of electrons, protons, photons, etc… But then we know from the way that galaxies behave that there’s lots of matter that can’t be like normal matter because it doesn’t interact with us….we can’t see it. The only effect we can see is its gravitational effect. We have no idea what this dark matter is but there are plenty of theories around with extra particles that are the dark matter candidate.
      Then there’s an even more mysterious thing called dark energy. That’s a kind of filed that fills space and acts like a negative pressure making the universe expand even faster. Again we don’t really know what this is but there are some theories.

    • Photo: Kristian Harder

      Kristian Harder answered on 21 Nov 2013:

      It really depends on how closely you look at it.

      – the Universe is a large collection of galaxies with a bit of energy and
      radiation scattered about

      – galaxies are large collections of stars, black holes, planets,
      and maybe dark matter. Black holes are pretty much made
      from squashed up stars and thus contain
      pretty much the same material, except in a rather extreme state. And we
      have no idea what dark matter is. In fact, we have so little idea of what it
      is that it might even be a misunderstanding in the first place, and not exist
      at all. We think it’s there because there seems to be invisible extra mass in
      the galaxies, but there’s still a chance we just don’t understand gravity
      well enough to really say that.

      – stars and planets typically contain atoms, molecules and the like. Within
      stars, the atoms are ionized, meaning their electrons go their separate
      ways, and some stars are so dense that they are pretty much just massive
      nuclei (“neutron stars”), but for the most part things are happening at the
      level of atoms here.

      – atoms and molecules consist of protons and neutrons (in the nuclei) and
      electrons (in their hull). Electrons seem to be really elementary, meaning
      we stop there. We haven’t been able to break down electrons into smaller
      pieces, and maybe we never will – but we’ll keep trying.

      – protons and neutrons are made from smaller particles called quarks,
      and a lot of so-called “gluons” to make them stick together. And as much
      as we try, so far we can’t break down quarks any further, and so this is
      where the story ends. For now. 🙂

      So, that’s the picture. Pretty much the entire universe consists of huge numbers of tiny particles: electrons, quarks, and a few more that I didn’t mention because they are a bit odd, in the sense that they only ever appear for a very short time and then immediately disappear again, or in the sense that they are very difficult to see like for example the so-called neutrinos.
      And at many different size scales between extremely tiny and extremely large, these little bits tend to organize themselves into groups such as atoms, people, stars, galaxies. It’s quite an interesting and impressive place, this universe we happen to live in. 🙂