ASTRONOMY was once a purely visual science. It began with people gazing up at the night sky in wonder and evolved into an optical quest to understand what photons can tell us about the universe. These days astronomers have expanded their quest into the realm of the unseen, where unknown forms of matter and energy are not only hard to see, but by definition invisible.
This new brand of astronomy demands much from our imaginations and often challenges common sense: that which we cannot perceive is hardest to accept. Throughout the history of science, invisible entities such as the Copernican…
