Two rival teams — the High-Z Supernova Search Team (led by Brian Schmidt, with Adam Riess as principal author of the analysis, and Robert Kirshner as co-author and doctoral mentor of both) and the Supernova Cosmology Project (led by Saul Perlmutter) — independently and almost simultaneously discover, using type Ia supernovae as standard candles, that the expansion of the universe is accelerating. The finding implies the existence of dark energy and was named "breakthrough of the year" by Science magazine in 1998. Riess, Schmidt, and Perlmutter shared the 2011 Nobel Prize in Physics for this discovery.