The Herschel Medal is awarded for "investigations of outstanding merit in observational astrophysics".
Simon Lilly receives the award for the discovery of the large change in the rate at which the Universe has been forming stars over the last 10 billion years. In the so-called 'Canada-France Redshift Survey', which was undertaken with colleagues in France and Canada between 1992 and 1996, Lilly (then at the University of Toronto) carried out the first systematic study of 'normal' galaxies that were sufficiently distant that they provide information about the Universe when it was less than a half of its current age of 14 billion years. These galaxies are 'normal' in the sense that they are similar to the Milky Way, the galaxy in which the Sun is found. Based on the data gathered in this survey, Lilly and his co-workers estimated the rate at which the Universe as a whole must be forming new stars and discovered that this rate was about ten times higher, at that earlier time, than it is now.
Understanding why the birth-rate of new stars has changed so dramatically with cosmic time and why the Universe appears to be 'running out of steam' in its ability to make new stars, is now a major focus of astrophysics and cosmology. These questions also guide the activities in Lilly's group at ETH since he moved to Zurich in 2002.
The award ceremony will be held at the National Astronomy Meeting of the Royal Astronomical Society in July.