In the new study, Riess and his colleagues used the Hubble Space Telescope to study 70 Cepheid variable stars in the Large Magellanic Cloud (LMC), one of the Milky Way’s satellite galaxies. Cepheid variables dim and brighten at predictable rates and are therefore “standard candles” that allow astronomers to calculate distances.
(Another kind of standard candle, the star explosions known as Type 1a supernovae, enables scientists to measure distances even farther out into space. Riess, Schmidt and Perlmutter’s studies of Type 1a supernovae led to their Nobel-winning discovery.)
Riess and his team also incorporated observations made by the Araucaria Project, a collaboration involving researchers in the United States, Europe and Chile, who studied various LMC binary star systems, noting the dimming that occurred when one star passed in front of its neighbor. This work provided additional distance measurements, helping the study team to improve their understanding of the Cepheids’ intrinsic brightness.