John Tonry: The Accelerating Universe

An astonishing discovery of the last 20 years was that the Universe is expanding faster now than it was billions of years ago. The discovery led to the concept of “dark energy,” a new and mysterious pressure that fills the Universe, and is now a major theme in cosmology.

Observations of “Type 1a Supernovae” – exploding stars in far distant galaxies – were used to measure the distance of the host galaxy independent of its cosmological recession velocity. These galaxies are so far away that the light travel time creates a “time machine” that allows us to compare today’s expansion of the Universe with the expansion five billion years ago. John Tonry’s group, the “High-z” team, took the lead in the discovery thanks to observations from Maunakea using a new, super-sized digital camera built at the IFA that was mounted on the Canada France Hawaii Telescope, and the spectrograph on the new Keck 10-meter telescope.

The teams had expected to find that expansion of the Universe was slowing; instead, their data showed that the Universe has been increasing its rate of expansion and this is attributed to dark energy, a property of the Universe unrecognized before.

John Tonry’s contribution was recognized by the 2011 Nobel Prize in Physics and by the 2014 Breakthrough Prize.

“It was exhilarating to work right on the bleeding edge of large detector arrays, large telescopes, computers, software, with a clock ticking to get the Hubble Space Telescope pointed before the supernova faded away…. The next step is to figure out exactly what “dark energy” means, by much better observations or perhaps just a good idea.”  —  John Tonry