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Asked by lmcginley to Adam, Chris, Eleanor, Jessamyn, Sinead on 11 Nov 2013.
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Christian Wirtz answered on 11 Nov 2013:
As far as we know, mostly hydrogen. Hydrogen is the simplest element with one proton and one electron and when enough of it accumulates it can form a star which fuses the hydrogen into all the other elements that exist, like helium, carbon and oxygen.
There is also something called “dark matter” which has that name because we cannot see it but know it is there. We can observe its gravitational effects (that is, it alters the movement of planets and asteroids in its vicinity) but have no visual image of it. There are speculations that this is made of neutrinos or other sub-atomic particles but we are not sure.
Maybe Adam can say a bit more about this?
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Adam Murphy answered on 11 Nov 2013:
Hey, cool question.
The bulk of the universe that we can see is made of hydrogen and helium, the first two elements. Stars are made of this stuff and so are things like nebula and all the clouds of stuff between stars and galaxies (Called the interstellar medium or the intergalactic medium). There are only tiny amounts of the elements we find on Earth.
But, this is just what we can see, and according to calculations about how fast the universe is expanding, 95% of matter is unaccounted for. We’ve called this stuff dark matter! There are experiments in CERN to try and find out what it’s made of and how it works. But it’s hard to do that because it doesn’t interact with light, so we can’t see it.
There are some labs though that don’t believe dark matter is the answer, they think there’s something else to add to the theory of gravity!
Hope that helps!
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