Dark Matter

demonstrate an understanding of the possible nature and significance of dark matter
demonstrate an understanding of the significance of dark energy

What is Dark Matter?

We can see stars because they give off light. What about all the stuff out there which does not give of light, or any other type of detectable radiation? This is dark matter. Some scientists think that as much as 95% of the Universe may be made of dark matter. Certainly our galaxy contains a lot. We cannot see much of our galaxy because it is obscured by dark matter. We have learnt more about the cosmos in the last 50 years than we did in all recorded history before but, despite this, the majority of what is out there is a BIG mystery.

Some of it could be the same material that the planets are made of and a lot could be dead stars, brown dwarfs and the like. It is thought that at the centre of our galaxy, and most other galaxies, is a super giant black hole.

screenshot from the 1922 film Nosferatu	pic NASA
There is an awful lot of stuff out there we just can't see. We call this material Dark Matter.	We know of dark matter from its gravitational effects on the matter that we can see. Here it acting like a lens, bending the light from galaxies behind it.

How much dark matter is actually out there?

This is a very important question. If there is enough dark matter then, because of its gravity, the Universe may stop expanding. It may even start to start shrinking and eventually collapse.

Don't panic though, astronomers now believe that the Universe will keep expanding. This is due to something called Dark Energy. In fact astronomers now know that the Universe is actually speeding up in its expansion.

Dark energy, according to very recent theories, exists uniformly in all space and somehow pushes outwards in all directions causing this acceleration. It is a form of energy and so it has an equivalent mass, as mass and energy are interchangeable.

It is now believed that 23.3% of the Universe is made up of dark matter and 72.1% is made up of dark energy. The rest, only about 5%, is made of atoms.