Astronomers say there is more to the Universe than meets the eye. From the way
that stars and galaxies move through space, it is clear that they are being
tugged by some invisible force. But what is responsible for that force?
THE DUTCH astronomer Jan Oort was one of the first to realise, in the early
1930s, that the only way to explain the behaviour of stars in our immediate
neighbourhood was to imagine that some dark, invisible matter filled the
greater part of space. At the time, astronomers had established that the stars
of the Milky Way Galaxy are…
