Scientists studying the deepest picture of the Universe, taken by the Hubble Space Telescope, have been left with a big poser: where are all the stars? The Ultra Deep Field is a view of one patch of sky built from 800 exposures. The picture shows faint galaxies whose stars were shining just a few hundred million years after the Big Bang. "Our results based on the Ultra Deep Field are very intriguing and quite a puzzle," says Dr Andrew Bunker, of Exeter University, UK, who led a team studying the new data." "They're certainly not what I expected, nor what...