Authors: Alister W. Graham
Abstract: In the last issue of SKY & SPACE (DEC/JAN 1998/99), I discussed one of the hottest topics in modern astronomy - dark matter - so-called because, whatever it is, it doesn't give off any detectable light. Dark matter could be comprised of unseen gas clouds, lots of black holes, burned-out stars, itinerant planets or any one of a number of other things that possess mass. Yet if it can't be seen, why do astronomers believe it exists in the first place? Because measurements of our Universe - and, in particular, the motions of galaxies - indicate that there must be a lot more mass out there than we can actually see. Astronomers refer to this as the 'missing mass' problem.