Amazing Kids! Magazine

Dark Matter

By Megan Bianca Yin Lee, Age 10, Singapore


What is the universe made of?  This question isn’t easily answerable.

The starting ingredient is that the universe has a “normal” matter component and this includes the stars, planets, comets and all living and nonliving things.  This “normal” matter is known as baryonic matter, which is made up of atoms as its most basic level.  You would think there would be nothing else to add into this mix but at least since the 1930s we have known of other more mysterious substances that make up our universe.

Other than baryonic matter there is another ingredient that makes up around 26% of the universe- dark matter (another mystery substance called dark energy makes up the balance but we’ll go into that at another time).  Two astronomers, Jan Hendrik Oort and Fritz Zwicky, are credited with discovering or rather suggesting that dark matter must exist in the 1930s.

While it is possible to use electron microscopes to see the atoms of baryonic matter no one has seen dark matter.  Dark matter does not emit nor reflect light.  Scientists deduce the existence of dark matter by the gravitational effects it has on other objects.

Firstly, astronomers deduced that certain galaxies were moving much faster than they were suppose too.  This led to the view that there was some extra unidentified mass (ie dark matter) exerting a powerful pull on these objects.  If this dark matter did not exist then these galaxies would just scatter at their observed velocities.

Since then the observation known as gravitational lensing has also been offered in support of the existence of dark matter.  Gravitational lensing says that light can be distorted or bent by mass. Astronomers have observed that light from distant galaxies are scattered in a way that cannot be explained solely by observable matter.  There must be other forms of matter exercising additional gravitational pull on the light.  Again, dark matter is suggested as the likely candidate for these observations.

No single explanation has been accepted on what makes up dark matter.  Various hypothetical elementary particles with exotic names such as WIMPS, WISPS and MACHOs have been put forward as the building blocks of dark matter.

The concept of dark matter is not accepted by everyone. Some scientists have proposed an alternative explanation ie ‘modified Newtonian dynamics’ (or MOND), which assumes that gravity behaves in a different way when it is applied to large objects such as stars and galaxies and this explains the discrepancies observed.  This is a very exciting area of science and many interesting experiments are being carried out to find the truth on dark matter!